1. A milkman adds a very small amount of baking soda to fresh milk
Ans: A milkman adds a very small amount of baking soda to fresh milk to increase alkalinity of milk that prevent to set as curd
6. Equal lengths of the 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?
Answer : Since HCl is strong acid and CH3COOH is a weak acid so being HCl a strong acid , dissociate more so that In test tube A, fizzing occur more vigorously.
7. Name a solution reacts with crushed egg-shells to give a gas that lime-water milky.
Answer H Cl , H Cl + CaCO3 ----> CaCl2 + Co2 + H2O
In this reaction carbon di oxide is given off that tumn lime water milky
8. Why does distilled water not conduct electricity, whereas rain water does.
Answer : Distilled water does not dissociate into ions. So it doe snot conduct electricity. Rain water has dissolved CO2 in it which form carbonic acid.
CO2 + H2O ----> H2CO3 This carbonic acid dissociate into ions.
H2CO3 + 2H2O-------à (H3O+)2 + CO3-2
These ions are responsible for electrical conductivity of rain water.
9. What is aqua-regia ?
Answer : A mixture (acid) of HCl and HNO3. Formed by mixing 3 moles of HCl and 1 mole of HNO3 i.e in the ratio 3:1.
This is one of the few acids that can dissolve metals like gold and platinum and use by gold smith . FIrst discovered by the famous muslim scientist Jabir-bin-Haiyan(known as the father of chemistry). It is a highly-corrosive fuming yellow liquid.
The name "Aqua Regia" is latin for "Royal Water". It was so named because it could dissolve the royal noble metals.Aqua regia works to dissolve gold, even though neither constituent acid will do so alone because, in combination, each acid performs a different task. Nitric acid is a powerful oxidizer, which will actually dissolve a tiny (virtually undetectable) amount of gold, forming gold ions.
The hydrochloric acid provides a ready supply of chloride ions, which react with the latter, thus taking the gold out of the solution. This allows further oxidation of gold to take place, and so the gold is dissolved.
10. Name the sodium compound which is used for softening hard water.
Answer : Hard water is water that has high mineral content .Hard water has high concentrations of Ca2+ and Mg2+ ions. Washing soda i.e., sodium carbonate (Na2CO3). is used for softening hard water.
It precipitates calcium and magnesium ions out of hard water.
11. Why should curd and sour substances not be kept in brass and copper vessels?
Answer : Curd and sour substances contain acids. Acids reacts with metals to give salt and hydrogen gas. So, if such substances are kept in copper container, the acid will react and the container will be corroded.
12. What is efflorescence?
14. What is universal indicator? Does Mg(OH)2 react with sodium hydroxide? If not, why?
Ans. Universal indicator is a mixture of several indicators which gives different colours at different pH values of the pH scale.
15.Why is Plaster of Paris written as CaSO4. ½ H2O ? How is it possible to have half a water
molecule attached to CuSO4?
Ans. The actual formula of Plaster of Paris is 2CaSO4.H2O which means that one molecule of
H2O is associated with two molecules of CaSO4. The formula for simplicity is written as CaSO4.
½H2O.
Ans: A milkman adds a very small amount of baking soda to fresh milk to increase alkalinity of milk that prevent to set as curd
2. Why do acids not show acidic behaviour in the absence of water?
Answer : In absence of water, acids do not dissociate H - So, they do not show acidic behaviour.
3. Alcohols and Glucose contain hydrogen but are not categorized as acids.
Answer: Alcohols and Glucose does not dissociate into ions on dissociation. So, the are not an acid.
4. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer : Plaster of Paris easily absorbs water and forms hard gypsum. Thus, if Plaster of Paris is not kept in a moisture-proof container, then all Plaster of Paris will get converted into gypsum.
Ca SO4 .1/2 H2O + 3/2 H2O ------> CaSO4 . 2H2O ( gypsum)
5. Why is calcium sulphate hemihydrates called 'Plaster of Paris'?
Answer: A big source of this substance is at Montmartre in Paris. So it is called as Plaster of Paris.
Answer : In absence of water, acids do not dissociate H - So, they do not show acidic behaviour.
3. Alcohols and Glucose contain hydrogen but are not categorized as acids.
Answer: Alcohols and Glucose does not dissociate into ions on dissociation. So, the are not an acid.
4. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer : Plaster of Paris easily absorbs water and forms hard gypsum. Thus, if Plaster of Paris is not kept in a moisture-proof container, then all Plaster of Paris will get converted into gypsum.
Ca SO4 .1/2 H2O + 3/2 H2O ------> CaSO4 . 2H2O ( gypsum)
5. Why is calcium sulphate hemihydrates called 'Plaster of Paris'?
Answer: A big source of this substance is at Montmartre in Paris. So it is called as Plaster of Paris.
6. Equal lengths of the 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?
Answer : Since HCl is strong acid and CH3COOH is a weak acid so being HCl a strong acid , dissociate more so that In test tube A, fizzing occur more vigorously.
7. Name a solution reacts with crushed egg-shells to give a gas that lime-water milky.
Answer H Cl , H Cl + CaCO3 ----> CaCl2 + Co2 + H2O
In this reaction carbon di oxide is given off that tumn lime water milky
8. Why does distilled water not conduct electricity, whereas rain water does.
Answer : Distilled water does not dissociate into ions. So it doe snot conduct electricity. Rain water has dissolved CO2 in it which form carbonic acid.
CO2 + H2O ----> H2CO3 This carbonic acid dissociate into ions.
H2CO3 + 2H2O-------à (H3O+)2 + CO3-2
These ions are responsible for electrical conductivity of rain water.
9. What is aqua-regia ?
Answer : A mixture (acid) of HCl and HNO3. Formed by mixing 3 moles of HCl and 1 mole of HNO3 i.e in the ratio 3:1.
This is one of the few acids that can dissolve metals like gold and platinum and use by gold smith . FIrst discovered by the famous muslim scientist Jabir-bin-Haiyan(known as the father of chemistry). It is a highly-corrosive fuming yellow liquid.
The name "Aqua Regia" is latin for "Royal Water". It was so named because it could dissolve the royal noble metals.Aqua regia works to dissolve gold, even though neither constituent acid will do so alone because, in combination, each acid performs a different task. Nitric acid is a powerful oxidizer, which will actually dissolve a tiny (virtually undetectable) amount of gold, forming gold ions.
The hydrochloric acid provides a ready supply of chloride ions, which react with the latter, thus taking the gold out of the solution. This allows further oxidation of gold to take place, and so the gold is dissolved.
10. Name the sodium compound which is used for softening hard water.
Answer : Hard water is water that has high mineral content .Hard water has high concentrations of Ca2+ and Mg2+ ions. Washing soda i.e., sodium carbonate (Na2CO3). is used for softening hard water.
It precipitates calcium and magnesium ions out of hard water.
11. Why should curd and sour substances not be kept in brass and copper vessels?
Answer : Curd and sour substances contain acids. Acids reacts with metals to give salt and hydrogen gas. So, if such substances are kept in copper container, the acid will react and the container will be corroded.
12. What is efflorescence?
Answer: Efflorescence is the loss of water (usually as evaporation to air) in an aqueous solution of salts, leaving behind crusts of solid salt crystals, called efflorescent salts
13.Explain the term olfactory indicator.
Ans. Substances whose odour changes in acidic or basic medium are called olfactory indicator. e.g. Eucalyptus (nilgiri) Oil, Onion & clove extract.
13.Explain the term olfactory indicator.
Ans. Substances whose odour changes in acidic or basic medium are called olfactory indicator. e.g. Eucalyptus (nilgiri) Oil, Onion & clove extract.
Ans. Universal indicator is a mixture of several indicators which gives different colours at different pH values of the pH scale.
Mg(OH)2 does not react with sodium hydroxide as both are bases having the same negative radical i.e. OH-
molecule attached to CuSO4?
Ans. The actual formula of Plaster of Paris is 2CaSO4.H2O which means that one molecule of
H2O is associated with two molecules of CaSO4. The formula for simplicity is written as CaSO4.
½H2O.
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