You have been provided with three test tubes. One of them contain
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    Acids, Bases and Salts
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    Why should curd and sour substances not be kept in brass and copper vessels?
    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.

    acid + metal → salt + Hydrogen gas
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    You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

    Divide the litmus paper in three parts and dip each part in three test tubes. The test tube in which litmus paper turns blue contains basic solution. The one in which red colour of litmus paper becomes light or purple contains water and the one in which there is no change in colour or it becomes more reddish contains acidic solution.
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    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?

    (ii) Illustration: Set up an apparatus as shown. Take some zinc granules in the test tube. Add about 5 ml dilute hydrochloric acid slowly. Soon the reaction between zinc and hydrochloric acid starts and hydrogen gas is evolved.

    (iii) Test for H2 gas: H2 gas is not soluble in water. When passed through soap solution, it gets trapped into bubbles which burn with explosion.

    (ii) Illustration: Set up an apparatus as shown. Take some zinc gran
    Fig. 2.1. Reaction of zinc granules with dilute hydrochloric and testing hydrogen gas by burning.

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    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.
    The end product is calcium chloride and the gas formed extinguishes a burning candle, it is CO2, the metal compound A must be calcium carbonate. Hence, the reaction between calcium carbonate and hydrochloric acid is as follows:

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    Why do HCl, HNO3 etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
    When HCl or HNO3 are mixed with water, they dissolve in water to form H+ or H3O+ ions which shows their acidic character. For example :

    HCl (aq) → H+ + Cl-
    H+ + H2O → H3O+

    When alcohols and glucose are mixed with water then they do not form ions. Hence they do not show acidic character.
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