A abampere (aA) The unit of electric current in the CGSeniu system, defined as that current that, if flowing through two parallel conductors of negligible cross section and infinite length, placed 1 cm apart in vacuo, would produce on each conductor a force of 1 dyne per centimeter of length. 1 abampere = 1 abcoulomb/s = r statampere (where c = speed of light in cm/s) = 10 ampere. aberration Imperfect image formation due to geometric imperfections in the optical elements of a system ablation 1 . The wasting of glacier ice by any process (calving, melting, evaporation, etc.). 2. The shedding of molten material from the outer sur- face of a meteorite or tektite during its flight through the atmosphere. absolute age The age of a natural substance, of a fossil or living organism, or of an artifact, obtained by means of an absolute dating method. See absolute dating method. absolute density Density in kg/m' or, more commonly, in g/cm\ both at STP. Cf. density, relative density abso
Chemical reactions and equations class 10 ncert chemistry MCQ & SAQ
Chemical reactions and equations class 10 ncert solution:
1. Why should a magnesium ribbon be cleaned before it is burnt in air?
Magnesium is a very reactive metal. When stored, it reacts with oxygen to form a layer of magnesium oxide on its surface. This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. The magnesium ribbon is cleaned by sand paper to remove this layer so that the underlying metal can be exposed to air.
2. Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminum sulfate → Barium sulfate + Aluminum chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
Answer
(i) H2 (g) + Cl2 (g) → 2HCl (g)
(ii) 3BaCl2 (s) + Al2(SO4)3 (s) → 3BaSO4 (s) + 2AlCl3 (s)
(iii) 2Na(s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
3. Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulfate in water react to give insoluble barium sulfate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Answer
(i) BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2NaCl (aq)
(ii) NaOH (aq) + HCl (aq) → NaCL (aq) + H2O (l)
Page No: 10
1. A solution of the substance ‘X’ is used for white washing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
Answer
(i) The substance ‘X’ is calcium oxide. Its chemical formula is CaO.
(ii) Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime).
CaO (s) + H2O (l) → Ca(OH)2 (aq)
Calcium Oxide (Quick Lime) + Water → Calcium Hydroxide (Slaked Lime)
2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.
Answer
Water contains two parts of hydrogen and one part oxygen. Therefore, during the electrolysis of water the amount of hydrogen gas collected in one of the test tubes is double than that of the oxygen produced and collected in the other test tube.
Page No: 13
1. Why does the color of copper sulfate solution change when an iron nail is dipped in it?
Answer
When an iron nail dipped in the copper sulfate solution then iron displaces copper from the copper sulfate because iron is more reactive than copper. Therefore the color of the copper sulfate solution changes.
The reaction involved here is:
Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
2. Give an example of a double displacement reaction other than the one given in Activity 1.10.
Answer
2KBr (aq) + BaI2 (aq) → 2KI (aq) + BaBr2 (aq)
3. Identify the substances that are oxidized and the substances that are reduced in the following reactions.
(i) 4Na (s) + O2 (g) → 2Na2O (s)
(ii) CuO (s) + H2 (g) → Cu (s) + H2O (l)
Answer
(i) Sodium (Na) is oxidized as it gains oxygen and oxygen gets reduced.
(ii) Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H2) gets oxidized to water (H2O).
Exercises
Page No: 14
1. Which of the statements about the reaction below are incorrect?
2PbO (s) + C (s) → 2Pb (s) + CO2 (g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidized.
(c) Carbon is getting oxidized.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
► (i) (a) and (b)
2. Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
► (d) displacement reaction.
3. What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
► (a) Hydrogen gas and iron chloride are produced.
4. What is a balanced chemical equation? Why should chemical equations be balanced?
Answer
A reaction which has an equal number of atoms of all the elements on both sides of the chemical equation is called a balanced chemical equation.Chemical reaction should be balanced to follow the law of conservation of mass.
5. Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulfide gas burns in air to give water and sulfur dioxide.
(c) Barium chloride reacts with aluminum sulfate to give aluminum chloride and a precipitate of barium sulfate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Answer
(a) 3H2 (g) + N2 (g) → 2NH3 (g)
(b) 2H2S (g) + 3O2 (g) → 2H2O (l) + 2SO2 (g)
(c) 3BaCl2 (aq) + Al2(SO4)3 (aq) → 2AlCl3 (aq) + 3BaSO4 (s)
(d) 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)
6. Balance the following chemical equations.
(i) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(ii) NaOH + H2SO4 → Na2SO4 + H2O
(iii) NaCl + AgNO3 → AgCl + NaNO3
(iv) BaCl2 + H2SO4 → BaSO4 + HCl
Answer
(i) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(ii) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(iii) NaCl + AgNO3 → AgCl + NaNO3
(iv) BaCl2 + H2SO4 → BaSO4 + 2HCl
7. Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminum + Copper chloride → Aluminum chloride + Copper
(d) Barium chloride + Potassium sulfate → Barium sulfate + Potassium chloride
Answer
(a) Ca(OH)2 + CO2 → CaCO3 + H2O
(b) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
(c) 2Al + 3CuCl2 → 2AlCl3 + 3Cu
(d) BaCl2 + K2SO4 → BaSO4 + 2KCl
8. Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a)Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium bromide(s)
(b) Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g)
(c) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)
Answer
(a) 2KBr (aq) + BaI2 (aq) → 2KI (aq) + BaBr2 (s): Double displacement reaction
(b) ZnCO3 (s) → ZnO (s) + CO2 (g): Decomposition reaction
(c) H2 (g) + Cl2 (g) → 2HCl (g): Combination reaction
(d) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g) : Displacement Reaction
9. What does one mean by exothermic and endothermic reactions? Give examples.
Answer
Chemical reactions that release energy in the form of heat, light, or sound are called exothermic reactions.
Example: C (g) + O2 (g) → CO2 + Heat Energy
Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
Example:
10. Why is respiration considered an exothermic reaction? Explain.
Answer
Respiration is considered as an exothermic reaction because in respiration oxidation of glucose takes place which produces a large amount of heat energy.
C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) + Energy
11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer
Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy.For Example:
Decomposition Reaction:
Combination Reaction:
CaO (s) + H2O (l) → Ca(OH)2 (aq)
Page No: 16
12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Answer
13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer
In a displacement reaction, a more reactive element replaces a less reactive element from a compound.
For Example: CuSo4 (aq) + Zn (s) → ZnSO4 (aq) + Cu (s)
In a double displacement reaction, two atoms or a group of atoms switch places to form new compounds.
For Example: Na2SO4 (aq) + BaCl2 (aq) → BaSO4 (s) + 2NaCl (aq)
14. In the refining of silver, the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.
Answer
2AgNO3 (aq) + Cu (s) → Cu(NO3)2 (aq) + 2Ag (s)
Silver Nitrate + Copper → Copper Nitrate + Silver
15. What do you mean by a precipitation reaction? Explain by giving examples.
Answer
A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.For Example:
Na2CO3 (aq) + CaCl2 (aq) → CaCO3 (s) + 2NaCl (aq)
Sodium Carbonate + Calcium Chloride → Calcium Carbonate + Sodium Chloride
In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction.
16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction
Answer
Oxidation Reaction: It is a chemical reaction in which gain of oxygen or loss of hydrogen takes place.
Reduction Reaction: It is a chemical reaction in which loss of oxygen or gain of hydrogen takes place.
17. A shiny brown-coloured element ‘X’ on heating in air becomes black in color. Name the element ‘X’ and the black coloured compound formed.
Answer
‘X’ is copper (Cu) and the black-coloured compound formed is copper oxide (CuO). The equation of the reaction involved in heating copper is given below.
18. Why do we apply paint on iron articles?
Answer
Iron articles are painted because it prevents them from rusting. When painted, the contact of iron articles from moisture and air is cut off. Hence, rusting is prevented.
19. Oil and fat containing food items are flushed with nitrogen. Why?
Answer
Oil and fat containing food items are flushed with nitrogen because nitrogen acts as an antioxidant and it prevents them from being oxidized.
20. Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Answer
Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemicals, etc.
For example, iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide.
4Fe + 3O2 + nH2O → 2Fe2O3.nH2O
Rancidity is the process of oxidation of fats and oils that can be easily noticed by the change in taste and smell is known as rancidity.
For example, the taste and smell of butter changes when kept for long.
Chemical reactions and equations class 10 ncert chemistry MCQ
Question : What happens when dilute hydrochloric acid is added to iron filling? Tick the correct answer
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced
(c) No reaction takes place
(d) Iron salt and water are produced
Answer : A
Question : A student added dilute HCl to a test tube containing zinc granules and made the following observations :
(a) the zinc surface became dull and black
(b) a gas evolved which burnt with a pop sound
(c) the solution remained colorless
(d) the solution becomes green in color
Answer : B
Question : The reaction of H2 gas with oxygen gas to form water is an example of
(a) combination reaction
(b) redox reaction
(c) exothermic reaction
(d) all of these reactions
Answer : A
Question : The condition produced by aerial oxidation of fats and oils in foods marked by unpleasant smell and taste is called:
(a) Antioxidation
(b) Reduction
(c) Rancidity
(d) Corrosion
Answer : C
Question : The blue flame in the below image represents the burning of which metal?
(a) Iron
(b) Copper
(c) Sodium
(d) All metal burn to give a blue flame
Answer : B
Question : In a context of redox reactions, the removal of hydrogen from a substance is known as
(a) Oxidation
(b) Dehydration
(c) Reduction
(d) Dehydrogenation
Answer : A
Question : Dissolving sugar is an example of
(a) Physical change
(b) Chemical change
(c) Redox Reaction
(d) None of these.
Answer : A
Question : The reaction in which two compounds exchange their ions to form two new compounds is -
(a) a displacement reaction
(b) a decomposition reaction
(c) an isomerization reaction
(d) a double displacement reaction
Answer : D
Question : When green coloured ferrous sulfate crystals are heated, the color of the crystal changes because
(a) it is decomposed to ferric oxide
(b) it loses water of crystallization
(c) it forms SO2
(d) it forms SO3
Answer : B
Question : A compound used for whitewashing is
(a) Quick lime
(b) Slaked Lime
(c) Blue vitriol
(d) Limestone
Answer : B
Question : A substance which oxidizes itself and reduces other is known as -
(a) oxidizing agent
(b) reducing agent
(c) both of these
(d) none of these
Answer : B
Question : Which of the following gasses can be used for storage
(a) Carbon dioxide or Oxygen
(b) Nitrogen or Oxygen
(c) Carbon dioxide or Helium
(d) Helium or Nitrogen
Answer : D
Question : When carbon dioxide is passed through lime water,
(a) calcium hydroxide is formed
(b) white precipitate of CaO is formed
(c) lime water turns milky
(d) The color of lime water disappears.
Answer : C
Question : Oxidation is a process which involves
(a) addition of oxygen
(b) addition of hydrogen
(c) removal of oxygen
(d) removal of hydrogen
Answer : A
Question : In an electrolytic cell where electrolysis is carried, anode has:
(a) Positive change
(b) Negative charge
(c) Connected to the negative terminal of the battery
(d) None of these is correct
Answer : A
Question : To indicate the presence of gaseous reactant or product, we use the symbol
(a) (Product)g or (Reactant)g
(b) (Product)- or (Reactant)-
(c) (Product). or (Reactant).
(d) Both (a) and (b)
Answer : D
Question : When dilute HCl is added to zinc pieces taken in a test tube
(a) No change takes place
(b) the color of the solution becomes yellow.
(c) A pungent smelling gas gets liberated.
(d) small bubbles of H2 gas appear on the surface of zinc pieces
Answer : D
Question : Which of the following is a physical change?
(a) Formation of curd from milk
(b) Ripening of fruits
(c) Getting salt from sea water
(d) Burning of wood
Answer : C
Question : A dilute ferrous sulfate solution was gradually added to the beaker containing acidified permanganate solution. The light purple color of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?
(a) KMnO4 is an oxidizing agent, it oxidizes FeSO4.
(b) FeSO4 acts as an oxidizing agent and oxidized KMNO4.
(c) The color disappears due to dilution; no reaction is involved.
(d) KMnO4 is an unstable compound and decomposes in the presence of FeSO4. to a colorless compound.
Answer : A
Question : A substance added to food containing fats and oils is called:
(a) Oxidant
(b) Rancid
(c) Coolant
(d) Antioxidant
Answer : D
Question : Lead nitrate Pb(NO3)2 on heating forms Lead oxide (PbO) solid and Nitrogen dioxide gas. What are the colors of lead oxide and nitrogen dioxide?
(a) White, Colorless
(b) White, Brown
(c) Yellow, Brown
(d) Yellow, Colorless
Answer : C
Question : One of the following is an endothermic reaction. This is
(a) Combination of carbon and oxygen to form carbon monoxide
(b) Combination of nitrogen and oxygen to form nitrogen monoxide
(c) Combination of glucose and oxygen to form carbon dioxide and water.
(d) Combination of zinc and hydrochloric acid to form zinc chloride and hydrogen
Answer : B
Question : Magnesium ribbon is rubbed before burning because it has a coating of
(a) basic magnesium carbonate
(b) basic magnesium oxide
(c) basic magnesium sulfide
(d) basic magnesium chloride
Answer : A
Question : Ethane (C2H6) on complete combustion gives CO2 and water. It shows that the results are in accordance with the law of conservation of mass. Then, the coefficient of oxygen is equal to
(a) 3
(b) 5/2
(c) 2
(d) 7/2
Answer : D
Question : The process of reduction involves
(a) addition of oxygen
(b) addition of hydrogen
(c) removal of oxygen
(d) removal of hydrogen
Answer : B
Question : Name the products formed when iron filings are heated with dilute hydrochloric acid
(a) Fe (III) chloride and water
(b) Fe (II) chloride and water
(c) Fe (II) chloride and hydrogen gas
(d) Fe (III) chloride and hydrogen gas
Answer : D
Question : Assertion: Zinc reacts with sulphuric acid to form zinc sulfate and hydrogen gas and it is a displacement reaction.
Reason: Zinc reacts with oxygen to form zinc oxide.
(a) Both A and R are true and R is the correct explanation of (a)
(b) Both A and R are true but R is not the correct explanation of (a)
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.
Answer : B
Question : A reaction of hydrogen with oxygen to form water is a
(a) Endothermic reaction
(b) Exothermic reaction
(c) Decomposition reaction
(d) Reaction not feasible
Answer : B
Question : What is observed when a solution of potassium iodide is added to a silver nitrate solution?
(a) No reaction takes place
(b) White precipitate of silver iodide is formed
(c) yellow precipitate of Agl is formed
(d) Agl is soluble in water.
Answer : C
Question : Magnesium ribbon is cleaned before burning. Why?
(a) It absorbs moisture from the atmosphere which interferes with burning.
(b) It’s outer layer forms oxides which interfere with burning.
(c) Dust from the atmosphere prevents its burning.
(d) All of the above
Answer : B
Question : Give the ratio in which hydrogen and oxygen are present in water by volume.
(a) 1:2
(b) 1:1
(c) 2:1
(d) 1:8
Answer : A
Question : The condition produced by aerial oxidation of fats and oils in foods marked by unpleasant smell and taste is called:
(a) antioxidation
(b) reduction
(c) rancidity
(d) corrosion
Answer : C
Question : To facilitate the electrolysis of water we add a few drops of acids like sulfuric acid or salts like NaCl. Because:
(a) It acts as a catalyst
(b) It prevents the decomposition of electrodes used.
(c) It increases the electrical conductivity of water.
(d) None
Answer : C
Question : Silver article turns black when kept in the open for a few days due to formation of
(a) H2S
(b) AgS
(c) AgSO4
(d) Ag2S
Answer : D
Question : Which of the following does not involve a chemical reaction?
(a) Digestion of food in our body
(b) Process of respiration
(c) Burning of candle wax when heated
(d) Melting of candle wax on heating
Answer : D
Question : When Ag is exposed to air it gets a black coating of
(a) AgNO3
(b) Ag2S
(c) Ag2O
(d) Ag2CO3
Answer : B
Chemical reactions and equations class 10 ncert chemistry SAQ
Q 1. 2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime. What will be your observation in this case? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction. [Delhi 2019]
The color of salt will change from white to gray.
It is a photochemical decomposition reaction.
Q 2. Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity. [CBSE 2018]
(i) Energy supplied in the form of heat
Decomposition of ferrous sulfate
(ii) Energy supplied in the form of light:
Decomposition of silver chloride
(iii) Energy supplied in the form of electricity:
Electrolysis of water
Q 3. In the reaction: [CBSE 2018C]
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
(a) Name the compound
(i) Oxidized
(ii) Reduced
(b) Define oxidation and reduction on its basis
(a) (i) HCL is getting oxidized.
(ii) MnO2 is getting reduced.
(b) The removal of hydrogen from a substance is called oxidation. The removal of oxygen from a substance is called reduction.
Q 4. Classify the following chemical reactions as exothermic or endothermic: [CBSE 2017]
(i) Water is added to quick lime.
(ii) Dilute sulphuric acid is added to zinc granules.
(iii) When ammonium chloride is dissolved in water in a test tube it becomes cold.
(iv) The decomposition of vegetable matter into compost.
(v) Electrolysis of water.
(vi) Silver chloride turns gray in the presence of sunlight to form silver metal.
(i) Water is added to quicklime - Exothermic
(ii) Dilute sulphuric acid is added to zinc granules - Exothermic
(iii) When ammonium chloride is dissolved in water in a test tube it becomes cold - Endothermic
(iv) The decomposition of vegetable matter into compost - Endothermic
(v) Electrolysis of water - Endothermic
(vi) Silver chloride turns gray in the presence of sunlight to form silver metal - Endothermic
Q 5. Name the type of chemical reaction represented by the following equations: [CBSE 2017]
(ii) CaO(s) + H2O(l) → Ca(OH)2 (aq)
(iii) Zn (s) + H2SO4 → ZnSO4(aq) + H2(g)
This is a decomposition reaction.
(ii) CaO (s) + H2O(l) → Ca(OH)2 (aq)
This is a combination reaction.
(iii) Zn(s) + H2SO4 → ZnSO4 (aq) + H2(g)
This is a displacement reaction.
Q 6. You must have tasted or smelt the fat-containing food material left for a long time. Such foods taste and smell bad. What is the reason for this? Name the phenomenon responsible for it. List two measures for its prevention. [CBSE 2016]
Food material left for a long time is oxidized by atmospheric oxygen. This changes the smell and taste of food.
Measures for prevention:
(i) Keep the food in air-tight containers.
(ii) Flush the food packets with nitrogen gas before sealing.
Q 7. Write chemical equations for the reactions taking place when: [CBSE 2016]
(i) Magnesium reacts with dilute HNO3.
(ii) Sodium reacts with water.
(iii) Zinc reacts with dilute hydrochloric acid.
(i) Mg + 2HNO3 (dil.) → Mg(NO3)2 + H2
(ii) 2Na + 2H2O → 2NaOH + H2
(iii) Zn + 2HCl → ZnCl2 + H2
Q 8. Take 3 g of barium hydroxide in a test tube, now add about 2g of ammonium chloride and mix the contents with the help of a glass rod. Now touch the test tube from outside. [CBSE 2016]
(i) What do you feel about touching the test tube?
(ii) State the inference about the type of reaction that occurred.
(iii) Write the balanced chemical equation of the reaction involved.
(i) The test tube becomes hot.
(ii) It is a decomposition reaction.
(iii) 2NH4Cl + Ba(OH)2 → BaCl2 + 2NH3↑ + 2H2O
Q 9. Balance the following chemical equations : [CBSE 2016]
(a) Mg + N2 → Mg3N2
(b) Al + Cl2 → AlCl3
(a) 3Mg + N2 → Mg3N2
(b) 2Al + 3Cl2 → 2AlCl3
Q 10. Define the term decomposition reaction. Give one example each of thermal decomposition and electrolytic decomposition. [CBSE 2016]
Those reactions in which a compound splits up into two or more simpler substances are called decomposition reactions.
Thermal decomposition:
Electrolytic decomposition:
Q 11. Look at the figure given below and answer the following questions: [CBSE 2015]
(i) State the color of the reactant and the product of the chemical reaction.
(ii) Write the chemical equation involved in this process.
(iii) Can we convert the product obtained back to reactant? Write the reaction involved.
(i) Color of reactant: Reddish brown
Color of product: Black
(iii) On passing H2 gas over hot CuO, the reaction can be reversed.
Q 12. (a) Write the essential condition for the following reaction to take place: [CBSE 2015]
2AgBr → 2Ag + Br2
Write one application of this reaction.
(b) Complete the following chemical equation of a chemical reaction:
(c) What happens when water is added to quick lime? Write a chemical equation.
The presence of sunlight is necessary for the reaction to take place.
This reaction is used in black and white photography.
(c) A hissing sound is heard. A brisk reaction takes place and calcium hydroxide is formed. A lot of heat is also produced
CaO + H2O → Ca(OH)2
Q 13. State reason for the following: [CBSE 2015]
(i) Potato chip manufacturers usually flush bags of chips with nitrogen gas.
(ii) Iron articles lose their shine gradually.
(iii) Foods should be kept in air-tight containers.
(i) Potato chips contain oils and fats, which react with atmospheric oxygen and become rancid. To protect chips from oxidation, nitrogen gas is passed through bags of chips which removes air (oxygen) from them. Nitrogen does not react with chips.
(ii) Iron article on keeping in the open for a long time reacts with oxygen and moisture and forms the rust on the surface. Articles lose their shine because of this.
(iii) Foods kept in the open are oxidized by the oxygen in the air. Their taste and smell change. When kept in air-tight containers, the food does not come into contact with air and is not spoilt.
Q 14. State the type of chemical reactions with chemical equations that take place in the following: [CBSE 2015]
(a) Magnesium ribbon is burnt in the air.
(b) Electric current is passed through water.
(c) Ammonia and hydrogen chloride gasses are mixed.
Q 15. Name the type of chemical reaction represented by the following equation: [CBSE 2015]
(a) CaO + H2O → Ca(OH)2
(b) 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3
(a) Combination reaction.
(b) Double displacement reaction (Precipitation)
(c) Decomposition reaction.
Q 16. (a) Consider the following chemical reaction
(i) Identify ‘X ’ and ‘Y ’.
(ii) The type of reaction. [BSE 2015]
(b) Identify the type of reaction from the following equations:
(i) HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
(ii) Fe(s) + CuSO4(aq) → FeSo4(aq) + Cu(s)
(a)
(i) ‘X’ Is Na2SO4 and Y is BaSO4
(ii) Na2SO4 + BaCl2 → BaSO4 + 2NaCl
(White ppt.)
The reaction is a precipitation reaction. It is also called a double displacement reaction.
(b)
(i) Double displacement reaction.
(ii) Displacement reaction.
Q 17. 2g of ferrous sulfate crystals are heated in a dry boiling tube.
[CBSE 2015, 2012]
(a) List any two observations.
(b) Name the type of chemical reaction taking place.
(c) Write the chemical equation for the reaction.
(a) Two observations are as follows:
(i) Green color of FeSO4 disappears and reddish-brown Fe2O3 is formed.
(ii) Smell of burning sulfur.
(b) Decomposition reaction.
Q 18. Write the chemical equation of the reaction in which the following changes have taken place with an example of each: [CBSE 2015,2014,2011]
(a) change in color.
(b) change in temperature.
(c) formation of a precipitate.
(a) Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag
The solution will become blue in color and shiny silver metal will be deposited.
(b) NaOH + HCl → NaCl + H2O + Heat
The temperature will increase because heat will evolve.
Yellow precipitate of PbI2 will be formed.
Q 19. Balance the following chemical equation: [CBSE 2015]
NaOH + H2SO4 → Na2SO4 + H2O
The balanced chemical equation is:
2NaOH + H2SO4 → Na2SO4 + 2H2O
Question-1
What is the method of balancing chemical equations?
Solution:
Hit and trial method is used for balancing simple chemical equations. In this method, coefficients before the symbols/formulae of the reactants and products are adjusted in such a way that the total number of atoms of each element on both the sides becomes equal.
Question-2
Why is it necessary to balance a chemical equation?
We know that, according to the law of conservation of mass, the total mass of all the atoms present in the reactants should be equal to that of all the atoms present in the products. This law will hold good only when the number of atoms of all types of elements on both sides is equal. Thus balancing of chemical equations is necessary so that the law of conservation of mass may be obeyed.
Question-3
In the equations given below, state giving reasons, whether substances have been oxidized or reduced.
(i) PbO + CO –> Pb + CO2
(ii) H2S + Cl2–>2HCl + S.
Solution:
(i) Carbon monoxide is oxidized as it gains oxygen.
(ii) Chlorine is reduced as it gains hydrogen.
Question-4
A sample of water weed was placed in water and exposed to sunlight. Bubbles of a gas are seen on the surface of the leaves.
(i) Name the gas that evolved.
(ii) Name the process taking place.
(iii) Write a balanced equation of reaction taking place.
Solution:
(i) Oxygen
(ii) Photosynthesis
(iii) 6CO2 + 6H2O —> C6H12O6 + 6O2.
Question-5
Give balanced equations, wherever possible, or where this is not possible, explain the following by means of examples:
i) A reaction which gives out heat.
ii) A reaction which takes place with the help of sunlight.
iii) A reaction which is brought about by electric current.
iv) Reversible reactions.
(v) A reaction with a solid and gas which produces heat.
Solution:
Question-6
Balance the following chemical equations:
Question-7
Write the uses of decomposition reactions.
Solution:
The decomposition reactions carried out by electricity are used to extract several metals from their naturally occurring compounds like chlorides and oxides.
When passing electricity decomposes the fused metal chloride or metal oxide, then metal is produced at the cathode.
Question-8
What are the characteristics of chemical reactions?
Solution:
1. Evolution of a gas
2. Formation of a precipitate
3. Change in color
4. Change in temperature
5. Change in state.
Question-9
Can rancidity retarded by storing foods away from light?
In the absence of light, the oxidation of fats and oils present in food is slowed down and hence the development of rancidity is retarded.
Question-10
What are the different ways to be more informed about the chemical equation?
1. By indicating the “physical states” of the reactants and products.
2. By indicating the “heat changes” taking place in the reaction.
3. By indicating the “conditions” under which the reaction takes place.
A Name the type of chemical reaction represented by the following equation:
Answer.
(i) Combination reaction
(ii) Double displacement reaction (Precipitation reaction)
(iii) Decomposition reaction.
Write the chemical equation of the reaction in which the following changes have taken place with an example of each:
(i) Change in color
(ii) Change in temperature
(iii) Formation of precipitate
Answer.
(i)Cu (s) + 2AgNO3 (aq)———–> Cu(NO3)2(aq) + 2Ag
The solution will become blue in color and shiny silver metal will be deposited.
(ii) NaOH + HCl ———–> NaCl + H2O+ heat
The temperature will increase because heat will evolve.
(iii) Pb(NO3)2 (aq) + 2KI (aq)———–> Pbl2 (s) + 2KNO3 (aq)
Yellow ppt
Yellow precipitate of Pbi2 Will be formed
(a) Write the essential condition for the following reaction to take place:
2AgBr—-> 2Ag + Br2
Write one application of this reaction.
(b) Complete the following chemical equation of a chemical reaction 2FeS04 —
(c) What happens when water is added to a quick line? Write chemical equations.
Answer.
This reaction is used in photography.
(c) Slaked lime is formed with a hissing sound and a lot of heat is generated.
2g of ferrous sulfate crystals are heated in a dry boiling tube.
(i) List any two observations.
(ii) Name the type of chemical reaction taking place.
(iii) ‘Write the chemical equation for the reaction.
Answer.
(i) •Green color of Fe SO4 disappears and a reddish brown solid is formed.
• Smell of burning sulfur.
(ii) Decomposition reaction
Which products will be obtained when lead nitrate is heated simply? Write a balanced chemical equation for the reaction? State the type of chemical reaction that occurs in the change.
Answer. Lead monoxide, nitrogen dioxide and oxygen gas will be liberated.
It is a thermal decomposition reaction.
What is meant by a skeletal type chemical equation? What does it represent? Using the equation for electrolytic decomposition of water, differentiate between a skeletal chemical equation and a balanced chemical equation.
Answer. The equations in which gaseous are written in atomic form instead of molecular form and the equation is not balanced, are called skeletal type equations. They represent gaseous elements formed in atomic state and equation is not balanced
.Write balanced chemical equations for the following reactions.
(i) Silver bromide on exposure to sunlight decomposes into silver and bromine,
(ii) Sodium metal reacts with water to form sodium hydroxide and hydrogen gas.
Answer.
19.Identify the type of reaction(s) in the following equations.
(i)CH4 + 2O2 CO2 + 2 H2O
(ii) Pb(NO3)2 + 2KI ——–>Pbl2 + 2KNOs
(iii) CaO + H2O ——–> Ca(OH)2
(iv) CuSO4 + Zn ——–> ZnSO4 + Cu
Answer.
(i) Combustion reaction and oxidation reaction.
(ii)Double displacement reaction and precipitation reaction.
(iii) Combination reaction.
(iv) Displacement reaction.
Write a balanced equation for the reaction between magnesium and hydrochloric acid. Name the product obtained, identify the type of reaction.
Answer.
The product formed is magnesium chloride and hydrogen gas.
It is a displacement reaction.
.What is the color of ferrous sulfate crystals? How does this color change after heating?
Answer.The color of ferrous sulfate is pale green. The color changes to reddish brown on heating due to the formation of iron (III) oxide.
Give an example each for thermal decomposition and photochemical decomposition reactions. Write relevant balanced chemical equations also.
Thermal decomposition reaction:
Photochemical decomposition reaction:
Why does the color of copper sulfate solution change when an iron nail is dipped in it? Write two observations.
Answer. It is because displacement reactions take place.
Iron displaces copper from copper sulfate solution and forms pale green
coloured solution of FeS04 and reddish brown copper metal gets deposited.
Fe(s) + CuS04(aq) ——–> FeS04(aq) + Cu(s
. Translate the following statement into chemical equation and then balance it Barium chloride reacts with aluminum sulfate to give aluminum chloride and a precipitate of barium sulfate. State the two types in which this reaction can be classified.
Answer. 3BaCl2(aq) + A12(S04)3(aq) ——–> 3BaS04(s) + 2AlCl3(aq)
It can be classified as double displacement as well as precipitation.
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer. In decomposition reaction, a compound is broken down into simpler compounds or elements, e.g.
Combination reaction is a reaction in which two or more elements or compounds combine to form a new compound, e.g.
Thus, decomposition and combination reactions are opposite to each other.
Chemical reactions and equations class 10 ncert chemistry long question
.Describe an activity to observe what happens when quick lime is added to water taken in a beaker. State two important observations and name the type of reaction taking place.
Answer.
Aim: To observe what happens when quicklime is added to water taken in a beaker.
Materials Required:- Quicklime (calcium oxide), water, beaker.
Procedure:
1. Take 5 g of calcium oxide in a beaker.
2. Add water to it slowly.
3. Touch the beaker.
4. Note down the observations.
Observation: Calcium oxide reacts with water
vigorously to form calcium hydroxide with the evolution of heat.
Chemical Reaction:
Conclusion: The reaction between CaO (Calcium oxide) and H2O is a combination reaction. It is an exothermic process because heat is evolved.
The following diagram displays a chemical reaction. Observe carefully and answer the following questions
(a) Identify the type of chemical reaction that will take place and define it. How will the color of the salt change?
Write the chemical equation of the reaction that takes place.
(c) Mention one commercial use of this salt.
Answer. (a) Photochemical decomposition reaction: Those reactions in which a compound breaks down into simple substances in the presence of light are called photochemical decomposition reactions. The color of salt will change from white to gray.
(c) Silver chloride is used in photography.
What is rancidity? Mention any two ways by which rancidity can be prevented.
Answer. The process in which the taste and smell of food gets spoiled is called rancidity. It happens due to oxidation.
Prevention from rancidity:
(i) Antioxidants are added to fatty acids to prevent oxidation, e.g. chips are packed in presence of nitrogen gas which prevents spoilage by oxidation.
(ii)Food should be kept in an airtight container in the refrigerator.
What is meant by a chemical reaction?
Answer. The reaction representing a chemical change is called a chemical reaction.
35.AgN03(aq) + NaCl(aq)——————– > AgCl(s)4↓ + NaN03(aq)
FeS + H2S04————- > FeS04 + H2S↑
Consider the above mentioned two chemical equations with two different kinds of arrows (↑and ↓) along with the product. What do these two different arrows indicate?
Ans,↑shows the gas is evolved whereas ↓shows the insoluble substance (precipitate) is formed.
Using a suitable chemical equation, justify that some chemical reactions are determined by:
(i) change in color, (ii) change in temperature.
Answer.
38.(a) A solution of substance ‘X’ is used for white washing. What is the substance ‘X’? State the chemical reaction of ‘X’ with water.
(b) Why does the color of copper sulfate solution change when an iron nail is dipped in it?
Answer.
(a) ‘X’ is calcium oxide (CaO).
CaO(s) + H2O(l) —–> Ca(OH)2(aq) + heat
(a) It is because iron displaces copper from CuS04 to form FeS04 which is pale green.
Fe(s) + CUS04 (aq)—–> FeS04(aq) + Cu(s)
Blue Pale green
Q 1. (a) What is a balanced chemical equation? Why should chemical equations be balanced?
(b) Write the chemical equation of the reaction in which the following changes have taken place: [CBSE 2017 C]
(i) Change in color
(ii) Change in temperature
(iii) Formation of a precipitate.
(a)
A chemical equation in which the total mass of the reactants is equal to the total mass of the products is called a balanced chemical equation.
It may also be defined as a chemical equation in which the number of atoms of each element is equal on the reactant side as well as on the product side.
It is only after balancing the chemical equation that we can find out how much of each product will be formed from certain quantities of the reactants, in terms of the law of conservation of mass.
(b) Chemical equations corresponding to different changes are given below:
(i) Change in color
(ii) Change in temperature
(iii) Formation of a precipitate
Q 2. (a) Balance the following chemical equations: [CBSE 2016]
(i) NaOH + H2SO4 → Na2SO4 + H2O
(ii) PbO + C → Pb + CO2
(iii) Fe2O3 + Al → Al2O3 + Fe + Heat
(b) Write the balanced chemical equations for the following reactions:
(i) Barium chloride + Potassium sulfate → Barium sulfate + Potassium chloride
(ii) Zinc + Silver nitrate → Zinc nitrate + Silver
(a) (i) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(ii) 2PbO + C → 2Pb + CO2
(iii) Fe2O3 + 2Al → Al2O3 + 2Fe + Heat
(b) (i) BaCl2 + K2SO4 → BaSO4 + 2KCl
(ii) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
Q 3. (a) Can we stir silver nitrate solution with a copper spoon? Why or why not?
Support your answer with reason.
(b) Why is a brown coating formed on the iron rod when the iron rod is kept dipped in copper sulfate solution for some time? What change will be observed in the color of the solution?
(c) A green coating develops on the copper vessel in the rainy season. Why? [CBSE 2015]
(a) We cannot stir silver nitrate with a copper spoon. Copper being more reactive than silver displaces silver from silver nitrate, that is, a reaction will take place.
(b)
Iron being more reactive than copper displaces copper from copper sulfate by the following reaction:
Brown coating of copper is deposited on the iron rod. Color of the solution becomes green due to the formation of ferrous sulfate.
(c) Copper reacts with moist carbon dioxide in the air in the rainy season and a green coating is formed. This is due to the formation of copper carbonate.
Q 4. (a) Illustrate an activity along with a labeled diagram, to show that a change in the state of matter and change in temperature takes place during a chemical reaction.
(b) Write balanced chemical equations for the following reactions:
(i) Natural gas burns and combines with oxygen to produce carbon dioxide and water.
(ii) Ferrous sulfate crystals on heating break up into ferric oxide, sulfur dioxide and sulfur trioxide. [CBSE 2015]
(a)
Take about 5g of quick lime in a beaker and add to it about 50 mL of water. A brisk reaction takes place and a lot of heat is generated.
CaO + H2O → Ca(OH)2 + HeatReaction of Quick Lime with Water
Quick lime is a white solid but after the reaction, calcium hydroxide is formed which is soluble in water and a clear solution is obtained.
Thus, there has been a change in the state of matter and a change in temperature.
(b) (i) CH4 + 2O2 → CO2 + 2H2O
(ii) 2FeSO4.7H2O → Fe2O3 + SO2 + SO3 + 14H2O
Q 5. (a) Explain two ways by which food industries prevent rancidity.
(b) Discuss the importance of decomposition reactions in the metal industry with three points. [CBSE 2015]
(a) (i) Rancidity can be prevented by adding antioxidants to food containing fat and oil. Example: Butylated hydroxy anisole is added to butter as an antioxidant.
(ii) It can be prevented by packaging fat and oil-containing foods in nitrogen gas.
(b) (i) Molten NaCl is electrolytically decomposed to form sodium metal.
(ii) Aluminum metal is obtained by the electric decomposition of bauxite ore mixed with cryolite.
(iii) Carbonate ores are thermally decomposed to give metal oxide which on reduction gives metal.
.Giving an example lists two pieces of information which make a chemical equation more useful (informative).
Answer.
(i) Physical state of reactants must be mentioned, e.g.
2H2 (g) + O2 (g)——– > 2H20 (l)
(ii) Conditions in which a reaction takes place are written on the arrow head, e.g.
Consider the following chemical reaction
X + Barium chloride——–> Y + Sodium chloride
(White ppt)
(a) Identify ‘X’ and ‘Y’
(b) The type of reaction
(a) ‘X’ is Na2SO4 and Y is BaSO4.
(b) The type of reaction
Na2SO4 + BaCl2—–> BaSO4 + 2NaCl
(White ppt)
The reaction is a precipitation reaction. It is also called a double displacement reaction.
Name the reducing agent in the following reaction:
3MnO2 + 4Al———— > 3Mn + 2Al2O3
State which is more reactive, Mn or A1 and why?
Answer. ‘Al’ is a reducing agent.
‘AT is more reactive than Mn v ‘Al’ displaces Mn from its oxide.
5.(i) Write a balanced chemical equation for the process of photosynthesis.
(ii)When do desert plants take up carbon dioxide and perform photosynthesis?
Answer.
(ii) In desert plants the stomata are open at night. They take CO2 at night and is stored in the form of acid and is used during day time for photosynthesis.
(a) Define a balanced chemical equation. Why should an equation be balanced?
(b) Write the balanced chemical equation for the following reaction:
(i) Phosphorus burns in the presence of chlorine to form phosphorus pentachloride.
(ii) Burning of natural gas.
(iii) The process of respiration.
Answer.
(a) Balanced chemical equation has an equal number of atoms of different elements in the reactants and products. According to the law of conservation of mass, matter can neither be created nor be destroyed in a chemical reaction.
(b)(i) P4 (s) + 10Cl2 (g) ———> 4PCl5 (S)
(i)CH4 (g) + 2O2 (g) ———> CO2 (g) + 2H2O(l) + heat energy
(iii) C6H12O6 (s) + 6O2 (g) + 6H2O ———> 6CO2 (aq) + 12H2O (l) + energy
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