Q1. Why does not silver evolve hydrogen on reacting with dil H2SO4
Ans.Silver do not evolve hydrogen on reacting with dil.H2SO4 as silver is less reactive metal than hydrogen
Q2. What is the sole of oxidizing agent is a reaction
Ans.The oxidizing agent supply the oxygen in a reaction or it removes the hydrogen.
Q3. Why are food particle preferably packed in aluminum foil?
Ans.Aluminium foil do not corrode in atmosphere even if kept for a long time because a protective coating of aluminium oxide (Al 2 O 3 ) is formed on the surface of the foil and stops any further reaction of the metal with air and water thus food particles do not get spoiled.
Q4.What happens when Carbon dioxide is added to lime water and what happens when it is added in excess
Ans.When Carbon dioxide gas is bubbled through lime water it turns milky but when added in excess then its milkiness disappears
Q5.Why should a magnesium ribbon be cleaned before burning in air?
Ans.Magnesium ribbon is cleaned before burning to remove the protective layer of basic magnesium carbonate from the surface of magnesium ribbon.
Q6. A solution of a substance ‘X’ is used for white washing
i. Name the substance ‘X’ and writes its formula.
ii. Write the reaction of the substance ‘X’ named in (i) above with water
Ans.(i). The substance whose solution is water is used for white washing is calcium oxide. Its formula is CaO.
(ii). CaO (s) + H 2 O Ca(OH) 2 (s)
Q7. Oil and fat containing food items are flushed with nitrogen. Why?
Ans. Oil and fat containing items get rancid due to oxidation with atmospheric oxygen. To prevent rancidity food items are flushed with nitrogen. Nitrogen do not reacts with oil and fat containing items.
Q8.A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
Ans. The brown coloured element ‘X‘ is copper. On heating in air it forms copper oxide, which is black in colour. 2CuS + O 2 2CuO
Q9. (a) Define Rusting
(b) Why do you apply paint an iron articles?
Ans. (a) The process of slow eating of the surface of metal iron when exposed to air for a longer period of time is called rusting.
(b) We apply paint on iron articles because it forms a protective coating on the surface of iron and we can protect it against rusting.
Q10.A student dropped few pieces of marble in dilute hydrochloric acid contained in a test tube. The evolved gas was then passed through lime water. What change would be observed in lime water? Write balanced chemical equation for both the change observed?
Ans. When marble reacts with dil. HCl, CO 2 gas evolved CaCO 3 (s) +2HCl (aq) CaCl 2 (aq) + H 2 O (l) + CO 2 (g) When this gas is evolved and is passed through lime water, becomes milky due to the formation of insoluble Calcium carbonate Ca (OH) 2 + CO 2 (g) CaCO 3 (s) +H 2 O (l) But when milkiness disappears i.e. when CO 2 gas is passed in excess through CaCO 3 (s) CaCO 3 (s) + CO 2 (g) +H 2 O (l) Ca (HCO 3 ) 2 (aq)
Q10. Why respiration is considered an exothermic reaction? Explain.
Ans. During respiration, we inhale oxygen from the atmosphere which reacts with glucose in your body cells to produce carbon dioxide and water. C 6 H 12 O 6 (aq) + 6O 2 6CO 2 (g) + 6H 2 O (l) + heat Heat is liberated in this process; hence respiration is considered an exothermic reaction.
Q11. A student dropped few pieces of marble in dilute HCI contained in a test tube. The gas evolved was passed through lime water. What change would be observed in lime water? Write chemical reactions for both the changes observed.
Ans.
Q12. When you mix solutions of lead (II) nitrate and potassium iodide, (i) What is the colour of the precipitate formed? Name the compound evolved? (ii) Write a balanced chemical reaction? (iii) Is this a double displacement reaction? Ans.
Q13. Give one example each of
(a) Thermal decomposition
(b) Electrolytic decomposition
(c) Photo decomposition
Ans.
Q14 What does one mean by exothermic and endothermic reactions? Give examples
Ans. A reaction in which energy is released in the form of heat or light is called exothermic reaction. Example of exothermic reaction are: CH 4 + 2O 2 CO 2 + 2H 2 O + heat 2Al + FeO 3 Al 2 O 3 + Fe + heat A reaction in which energy is absorbed from the surrounding and cooling is produced is called endothermic reaction. Example of exothermic reaction are: a. CaCO 3 CaO + CO 2 b. N 2 + O 2 2NO
Q15.Explain the following in terms of gain and loss of oxygen with two examples each?
a. Oxidation
b. Reduction
Ans. Oxidation- addition of oxygen or removal of hydrogen in a chemical reaction is called oxidation reaction. For example 2Cu +O 2 2CuO 4Al + 3O 2 2Al 2 O 3
Reduction- addition of hydrogen or removal of oxygen in a chemical reaction is called oxidation reaction. For example CuO +H 2 Cu +H 2 O H 2 S + Cl 2 2HCl +S
Q16.Explain the following terms with one example each.
a. Corrosion
b. Rancidity.
Ans. Corrosion- action of air, water, acid or other substance on metal surface to form oxides and carbonates is called corrosion. Corrosion of iron is called rusting. Green coating on copper and black coating on silver is examples of corrosion.
Rancidity-change in smell of food item containing fat and oil when kept open for longer time due to oxidation is called rancidity. To prevent rancidity food items are flushed with nitrogen or kept in airtight containers.
Ans.Silver do not evolve hydrogen on reacting with dil.H2SO4 as silver is less reactive metal than hydrogen
Q2. What is the sole of oxidizing agent is a reaction
Ans.The oxidizing agent supply the oxygen in a reaction or it removes the hydrogen.
Q3. Why are food particle preferably packed in aluminum foil?
Ans.Aluminium foil do not corrode in atmosphere even if kept for a long time because a protective coating of aluminium oxide (Al 2 O 3 ) is formed on the surface of the foil and stops any further reaction of the metal with air and water thus food particles do not get spoiled.
Q4.What happens when Carbon dioxide is added to lime water and what happens when it is added in excess
Ans.When Carbon dioxide gas is bubbled through lime water it turns milky but when added in excess then its milkiness disappears
Q5.Why should a magnesium ribbon be cleaned before burning in air?
Ans.Magnesium ribbon is cleaned before burning to remove the protective layer of basic magnesium carbonate from the surface of magnesium ribbon.
Q6. A solution of a substance ‘X’ is used for white washing
i. Name the substance ‘X’ and writes its formula.
ii. Write the reaction of the substance ‘X’ named in (i) above with water
Ans.(i). The substance whose solution is water is used for white washing is calcium oxide. Its formula is CaO.
(ii). CaO (s) + H 2 O Ca(OH) 2 (s)
Q7. Oil and fat containing food items are flushed with nitrogen. Why?
Ans. Oil and fat containing items get rancid due to oxidation with atmospheric oxygen. To prevent rancidity food items are flushed with nitrogen. Nitrogen do not reacts with oil and fat containing items.
Q8.A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
Ans. The brown coloured element ‘X‘ is copper. On heating in air it forms copper oxide, which is black in colour. 2CuS + O 2 2CuO
Q9. (a) Define Rusting
(b) Why do you apply paint an iron articles?
Ans. (a) The process of slow eating of the surface of metal iron when exposed to air for a longer period of time is called rusting.
(b) We apply paint on iron articles because it forms a protective coating on the surface of iron and we can protect it against rusting.
Q10.A student dropped few pieces of marble in dilute hydrochloric acid contained in a test tube. The evolved gas was then passed through lime water. What change would be observed in lime water? Write balanced chemical equation for both the change observed?
Ans. When marble reacts with dil. HCl, CO 2 gas evolved CaCO 3 (s) +2HCl (aq) CaCl 2 (aq) + H 2 O (l) + CO 2 (g) When this gas is evolved and is passed through lime water, becomes milky due to the formation of insoluble Calcium carbonate Ca (OH) 2 + CO 2 (g) CaCO 3 (s) +H 2 O (l) But when milkiness disappears i.e. when CO 2 gas is passed in excess through CaCO 3 (s) CaCO 3 (s) + CO 2 (g) +H 2 O (l) Ca (HCO 3 ) 2 (aq)
Q10. Why respiration is considered an exothermic reaction? Explain.
Ans. During respiration, we inhale oxygen from the atmosphere which reacts with glucose in your body cells to produce carbon dioxide and water. C 6 H 12 O 6 (aq) + 6O 2 6CO 2 (g) + 6H 2 O (l) + heat Heat is liberated in this process; hence respiration is considered an exothermic reaction.
Q11. A student dropped few pieces of marble in dilute HCI contained in a test tube. The gas evolved was passed through lime water. What change would be observed in lime water? Write chemical reactions for both the changes observed.
Ans.
Q12. When you mix solutions of lead (II) nitrate and potassium iodide, (i) What is the colour of the precipitate formed? Name the compound evolved? (ii) Write a balanced chemical reaction? (iii) Is this a double displacement reaction? Ans.
Q13. Give one example each of(a) Thermal decomposition
(b) Electrolytic decomposition
(c) Photo decomposition
Ans.
Q14 What does one mean by exothermic and endothermic reactions? Give examples
Ans. A reaction in which energy is released in the form of heat or light is called exothermic reaction. Example of exothermic reaction are: CH 4 + 2O 2 CO 2 + 2H 2 O + heat 2Al + FeO 3 Al 2 O 3 + Fe + heat A reaction in which energy is absorbed from the surrounding and cooling is produced is called endothermic reaction. Example of exothermic reaction are: a. CaCO 3 CaO + CO 2 b. N 2 + O 2 2NO
Q15.Explain the following in terms of gain and loss of oxygen with two examples each?
a. Oxidation
b. Reduction
Ans. Oxidation- addition of oxygen or removal of hydrogen in a chemical reaction is called oxidation reaction. For example 2Cu +O 2 2CuO 4Al + 3O 2 2Al 2 O 3
Reduction- addition of hydrogen or removal of oxygen in a chemical reaction is called oxidation reaction. For example CuO +H 2 Cu +H 2 O H 2 S + Cl 2 2HCl +S
Q16.Explain the following terms with one example each.
a. Corrosion
b. Rancidity.
Ans. Corrosion- action of air, water, acid or other substance on metal surface to form oxides and carbonates is called corrosion. Corrosion of iron is called rusting. Green coating on copper and black coating on silver is examples of corrosion.
Rancidity-change in smell of food item containing fat and oil when kept open for longer time due to oxidation is called rancidity. To prevent rancidity food items are flushed with nitrogen or kept in airtight containers.
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