Q. 1. What happens if sodium hydroxide is added to cupper ammonium sulphate solution and what is the inference?
Q 2. When lead dioxide reacts with concentrated HCl and produces a salt and water, the reaction is not called a neutral reaction why?
Answer: For a reaction to be called a neutral reaction the products should be only salt and water. But in the above reaction, Cl2 gas is also liberated.
Q 3.Define a base and acid in terms of proton.
Answer: A base is a proton acceptor and an acid is a proton donor.
Q 4. Answer these:
1) Name the anions that can be detected in the laboratory using dilute HCl or dilute H2SO4 and give the ionic equation common to both reactions.
2) Which property of the acid is indicated?
Answer:
Answer: 1) The blue crystals turn to white amorphous anhydrous powder. Hence concentrated H2SO4 acts as a dehydrating agent, removing the water of crystallization molecules from CuSO4.5H2O crystals.
Q6: Name two crystalline salts that do not have water of crystallization.
Answer: The chlorides of K, Na and Pb and the nitrates of K, Na, Pb, Ag, [NH4+] do not have water of crystallization.
Q 7. Why do acids not show acidic behavior in the absence of water?
Ans: Acids do not show acidic behaviour in absence of water because the dissociation of hydrogen ions from an acid occurs in presence of water only. It is hydrogen ions that are responsible for the acidic behaviour.
Q 8. How is NH4OH used as a laboratory reagent?
Answer: NH4OH is used to detect cations in their salt solutions by precipitating their hydroxides whose colour and solubility in excess NH4OH, identifies them.
Q 9. Name four gases that can be prepared in the laboratory using dilute H2SO4. Show how they can be prepared?
Answer: The four gases are:
1) H2 gas 2) CO2 gas 3) SO2 gas 4) H2S gas
Their respective methods of preparations are:
Q 10. While diluting concentrated H2SO4, what care must be taken and why?
Answer: While diluting concentrated H2SO4 never add water to concentrated acid; instead, add concentrated H2SO4 slowly with stirring to the volume of water. As this reaction is highly exothermic the heat produced will splash the acid and may cause burns.
Q 11. What is the cause of tooth decay?
Answer: The bacteria present in the mouth act on sugar and food particles remaining in the mouth after eating to produce acids. The acid produced lowers the pH in the mouth to 5.5 and begins to attack the hard enamel and corrode it resulting in tooth decay.
Q 12. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer: Plaster of Paris (POP) or calcium sulphate with half a molecule of water per molecule of the salt (hemi-hydrate) is a hygroscopic substance. Should it absorb a little water from the surroundings, it evolves heat and quickly sets to a hard porous mass hence it should be stored in a moisture-proof container to keep it dry
Q.13 A milkman adds a very small amount of baking soda to fresh milk.
Ans:
(a) By adding small amount of baking soda, the milkman shifts the pH of the fresh milk from 6 to slightly alkaline so that he can keep it for longer time as the milk in alkaline condition, does not set curd easily.
(b) Since, this milk is slightly basic than the usual milk, acids produced due to bacterial actions in it are neutralized by the base. Therefore, it takes longer time to set as curd.
Q.14.Give two important uses of washing soda and baking soda.
Ans: Uses of Washing Soda:
Uses of Baking Soda:
1. Sodium hydrogen carbonate is also ingredient in antacids. Being alkaline, it neutralizes excess acid in the stomach and provides relief.2. It is also used in soda-acid fire extinguishers.
Q. 15. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Ans: The fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added. This is because HCl is a stronger acid than CH3COOH and therefore produces hydrogen gas at a faster speed due to which fizzing occurs.
Q17. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Ans. Plaster of Paris (POP) should be stored in a moisture-proof container because Plaster of Paris, a powdery mass, absorbs water (moisture) to form a hard solid known as gypsum.
Ans: Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food.
Q19. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Ans: Hydrogen gas is usually liberated when an acid reacts with a metal.
Answer: When sodium hydroxide is added to cupper ammonium sulphate solution, no blue precipitate of Cu(OH)2 is seen, which is normally observed for Cu2+ ion. Hence it is an example of a complex salt.
Q 2. When lead dioxide reacts with concentrated HCl and produces a salt and water, the reaction is not called a neutral reaction why?
Answer: For a reaction to be called a neutral reaction the products should be only salt and water. But in the above reaction, Cl2 gas is also liberated.
Q 3.Define a base and acid in terms of proton.
Answer: A base is a proton acceptor and an acid is a proton donor.
Q 4. Answer these:
1) Name the anions that can be detected in the laboratory using dilute HCl or dilute H2SO4 and give the ionic equation common to both reactions.
2) Which property of the acid is indicated?
Answer:
Carbonate and Bicarbonate Ions 2H+ + CO32- ........> H2O + CO2
Q 5. 1) What do you observe when concentrated H2SO4 is added slowly to blue CuSO4 crystals in a test tube and why?
2) Is these any other way of observing the above result?
Q 5. 1) What do you observe when concentrated H2SO4 is added slowly to blue CuSO4 crystals in a test tube and why?
2) Is these any other way of observing the above result?
Answer: 1) The blue crystals turn to white amorphous anhydrous powder. Hence concentrated H2SO4 acts as a dehydrating agent, removing the water of crystallization molecules from CuSO4.5H2O crystals.
Q6: Name two crystalline salts that do not have water of crystallization.
Answer: The chlorides of K, Na and Pb and the nitrates of K, Na, Pb, Ag, [NH4+] do not have water of crystallization.
Q 7. Why do acids not show acidic behavior in the absence of water?
Ans: Acids do not show acidic behaviour in absence of water because the dissociation of hydrogen ions from an acid occurs in presence of water only. It is hydrogen ions that are responsible for the acidic behaviour.
Q 8. How is NH4OH used as a laboratory reagent?
Answer: NH4OH is used to detect cations in their salt solutions by precipitating their hydroxides whose colour and solubility in excess NH4OH, identifies them.
Q 9. Name four gases that can be prepared in the laboratory using dilute H2SO4. Show how they can be prepared?
Answer: The four gases are:
1) H2 gas 2) CO2 gas 3) SO2 gas 4) H2S gas
Their respective methods of preparations are:
2) Any carbonate salt and dilute H2SO4 gives CO2 gas.
3) Any sulphite salt and dilute H2SO4 gives SO2 gas.
4) Any sulphide salt and dilute H2SO4 gives H2S gas.
4) Any sulphide salt and dilute H2SO4 gives H2S gas.
Q 10. While diluting concentrated H2SO4, what care must be taken and why?
Answer: While diluting concentrated H2SO4 never add water to concentrated acid; instead, add concentrated H2SO4 slowly with stirring to the volume of water. As this reaction is highly exothermic the heat produced will splash the acid and may cause burns.
Q 11. What is the cause of tooth decay?
Answer: The bacteria present in the mouth act on sugar and food particles remaining in the mouth after eating to produce acids. The acid produced lowers the pH in the mouth to 5.5 and begins to attack the hard enamel and corrode it resulting in tooth decay.
Q 12. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer: Plaster of Paris (POP) or calcium sulphate with half a molecule of water per molecule of the salt (hemi-hydrate) is a hygroscopic substance. Should it absorb a little water from the surroundings, it evolves heat and quickly sets to a hard porous mass hence it should be stored in a moisture-proof container to keep it dry
Q.13 A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?
Ans:
(a) By adding small amount of baking soda, the milkman shifts the pH of the fresh milk from 6 to slightly alkaline so that he can keep it for longer time as the milk in alkaline condition, does not set curd easily.
(b) Since, this milk is slightly basic than the usual milk, acids produced due to bacterial actions in it are neutralized by the base. Therefore, it takes longer time to set as curd.
Q.14.Give two important uses of washing soda and baking soda.
Ans: Uses of Washing Soda:
1. Sodium carbonate (washing soda) is used in glass, soap, and paper industries.
2. It is used in the manufacture of sodium compounds such as Borax.
Uses of Baking Soda:
1. Sodium hydrogen carbonate is also ingredient in antacids. Being alkaline, it neutralizes excess acid in the stomach and provides relief.2. It is also used in soda-acid fire extinguishers.
3. It is used as baking powder in confectionery items like cake, pastry etc.
Q. 15. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Ans. When a solution of sodium hydrocarbonate (sodium hydrogencarbonate) is heated, sodium carbonate and water are formed with the evolution of carbon dioxide gas.
2NaHCO3 + heat → Na2CO3 + H2 O + CO2
Q. 16. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?
Ans: The fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added. This is because HCl is a stronger acid than CH3COOH and therefore produces hydrogen gas at a faster speed due to which fizzing occurs.
Q17. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Ans. Plaster of Paris (POP) should be stored in a moisture-proof container because Plaster of Paris, a powdery mass, absorbs water (moisture) to form a hard solid known as gypsum.
Ca SO4 . ½ H2 O + 11/2 H2 O → Ca SO4 . 2 H2O
Q 18 :Why should curd and sour substances not be kept in brass and copper vessels?
Q 18 :Why should curd and sour substances not be kept in brass and copper vessels?
Ans: Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food.
Q19. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Ans: Hydrogen gas is usually liberated when an acid reacts with a metal.
Take few pieces of zinc granules and add 5 ml of dilute H2SO4. Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.
2H2SO4 + Zn → Zn (SO4)2 + 2H2
2H2SO4 + Zn → Zn (SO4)2 + 2H2
We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.
Q 20: Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Q 20: Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Ans: CaCO3 (s) + HCI(aq) → CaCI2(aq) + CO2 + H2 O (I)
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