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17. What is an alfactory indicator ? Name two olfactory indicators. What is the effect of adding sodium hydroxide
heric paper turn when put in an alkaline solution ?
solution to these olfactory indicators ?
18. (a) What happens when an acid reacts with a metal ? Give chemical equation of the reaction involved
(1) Which gas is usually liberated when an acid reacts with a metal ? How will you test for the presence of
this gas?
19. While diluting an acid, why is it recommended that the acid should be added to water and not water to the
20. What happens when an acid reacts with a metal hydrogencarbonate ? Write equation of the reaction which
takes place.
21. (a) What happens when dilute hydrochloric acid is added to sodium carbonate ? Write a balanced chemical
equation of the reaction involved.
(b) Which gas is liberated when dilute hydrochloric acid reacts with sodium carbonate ? How will you test
for the presence of this gas?
22. What happens when an acid reacts with a base ? Explain by taking the example of hydrochloric acid and
sodium hydroxide. Give equation of the chemical reaction which takes place. What is the special name of
such a reaction ?
23. What happens when an acid reacts with a metal oxide ? Explain with the help of an example Write a
balanced equation for the reaction involved.
24. (a) What are organic acids and mineral acids?
(b) Give two examples each of organic acids and mineral acids.
(c) State some of the uses of mineral acids in industry.
25. What is meant by strong acids and weak acids ? Classify the following into strong acids and weak acids:
HCI, , CH,COOH H2SO4, HNO3, H2CO3, H SO
26. Why do HCI, H2SO, HNO3, etc.,
show acidic character in aqueous solutions while solutions of compounds
like CH1206 (glucose) and C2H,OH (alcohol) do not show acidic character ?
27. What is a neutralisation reaction ? Explain with an example. Give the chemical equation of the reaction
which takes place.
28. Why should curd and other sour foodstuffs (like lemon juice, etc.) not be kept in metal containers (such as
copper and brass vessels)?
29. (a) What is produced if an acid is added to a base ?
(b) Why does dry HCl gas not change the colour of dry litmus paper ?
(C) What colour does phenolphthalein indicator turn when added to an alkali (such as sodium hydroxide
30. (a) Why do acids not show acidic behaviour in the absence of water?
(b) Why does an aqueous solution of an acid conduct electricity ?
(c) Why does distilled water not conduct electricity whereas rain water does ?
please answer them schand book question
Answers
Answer:
17) Those substances which changes smell according to the medium of "acidity and alkalinity". Solution of Sodium hydroxide when added to the substance like onion or vanilla, which are the olfactory indicator, the smell of olfactory indicator is not indicated. Therefore, alkaline solution changes the smell.
18)a)When acids react with metals, they produce a salt and hydrogen gas.The general equation that describes the chemical reaction between an acid and metal is metal + acid = salt + hydrogen gas.
1)Hydrogen gas is liberated when an acid reacts with a metal. For example, when zinc metal reacts with dil. hydrogen is evolved and salt zinc chloride is formed as: It can be tested by bringing a burning candle near the gas.
19)So much heat is released that the solution may boil very violently, splashing concentrated acid out of the container and all this because the reaction is exothermic.So it is always safer to add acid to water, and not water to acid.
20)Acid + Metal hydrogen carbonate → Salt + Carbon dioxide + Water.
21) a)When dilute hydrochloric acid reacts with sodium carbonate, then sodium chloride, carbon dioxide and water are formed.
(b) CO2 gas is liberated during the reaction. When carbon dioxide gas formed in the form of brisk effervescence is passed through lime water, it turns the lime water milky.Carbon dioxide gas is liberated when hydrochloric acid reacts with sodium hydrogen carbonate. The gas liberated thus will pass through lime water and lime water turns milky due to the presence of carbon dioxide and further more if we do the same the solution becomes clear.
22)The reaction between an acid and a base is known as a neutralisation reaction. Often when an acid and base react a salt and water will be formed.Hydrochloric acid reacts with sodium hydroxide to form sodium chloride (a salt) and water.
23)When an acid is treated with a metal oxide, a salt and water are obtained. For example, when a small amount of copper oxide is added to sulphuric acid, colour of the solution becomes blue and the copper oxide dissolves. The blue colour of the solution indicates the formation of copper (II) sulphate.
24)a)Organic acids are acids present in plant materials and animals. These are naturally occuring acids. A mineral acid (or inorganic acid) is an acid derived from one or more minerals of the earth.
b)A mineral acid (or inorganic acid) is an acid derived from one or more minerals of the earth. Organic acids: Citric acid, lactic acid; Mineral acids: Hydrochloric acid, sulphuric acid.
c)Uses of mineral acids in industry:
Sulphuric acid is used in the manufacture of fertilizers, paints, dyes, detergents, etc.
Nitric acid is used for making fertilizers, explosives, dyes and plastics.
Hydrochloric acid is used for removing oxide film from steel objects, in textile, food and leather industries.
25)A strong acid is one that completely ionises in water to form a large amount of hydrogen ions whereas a weak acid only partially ionises in water and thus produces a small amount of hydrogen ions. HCl, H2SO4, HNO3 are strong acids; CH3COOH, H2CO3, H2SO3 are weak acids.
26)HCl, H2SO4 etc show acidic properties because they produce hydrogen ions when dissolved in water. The solution of compounds like alcohol and glucose do not show acidic character because they do not ionize in water to produce hydrogen ions or any other ions in solution.
27)A neutralization reaction can be defined as a chemical reaction in which an acid and base quantitatively react together to form a salt and water as products. In a neutralization reaction, there is a combination of H+ ions and OH– ions which form water.
28)Curd and other sour substances contains acids which can react with the metals of brass and copper vessels to form toxic (poisonous) metal compounds which can cause food poisoning and damage our health.
29)a)When an acid and a base are placed together, they react to neutralize the acid and base properties, producing a salt
b)Dry HCL it does not dissociate to give H+ ions. Acids dissociate to give ions only in the aqueous solution. In this, HCL is not in the aqueous form nor the litmus paper is wet, so the colour of the litmus paper does not change