Q7 of 216 Page 469

What happens when dilute hydrochloric acid is added to the following and write balanced chemical equations:

i. Bleaching powder


ii. Zinc granules


iii. Baking soda


OR


You have two solutions A and B. The pH of the solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of these is acidic and which one is basic?

i. Bleaching Powder is calcium Oxychloride. The chemical formula of bleaching powder is CaOCl2.


Bleaching powder reacts with dilute HCl to liberate Cl2 gas, water and Calcium Chloride.


CaOCl2(s) + 2HCl (aq)→ CaCl2(s) +Cl2 (g) +H2O (l)


ii. When dilute hydrochloric acid is poured on zinc granules, then zinc sulphate is formed along with the evolution of a gas. Zinc is more reactive than hydrogen, so displaced it from hydrochloric acid.


The gas evolved is hydrogen. We can test its presence by bringing a burning candle near the mouth of the test tube and hearing for a popping sound. Only hydrogen gas burns with a 'pop' sound.


2HCl (aq) + Zn (s)→ ZnCl2 (aq) + H2 (g)


iii. Mixing baking soda, or NaHCO3, with hydrochloric acid, or HCl, results in table salt, NaCl, as well as water, H2O, and carbon dioxide, CO2. These experiments can also demonstrate stoichiometry, which deals with the reactants and products in chemical reactions.”


NaHCO3(s) + 2HCl (aq)→ NaCl(s) + H2O (l) + CO2 (g)


This is a neutralization reaction it releases bubbles of carbon dioxide gas


OR


The character of acidic, basic and neutral is defined by the concentration of hydrogen ions [H+](mol/L). A solution with a concentration of hydrogen ions higher than 10-7mol/L is acidic, and a solution with a lower concentration is alkaline.


Using the formula,


pH=-log [H+],


a pH of 7 is neutral, a pH less than 7 is acidic, and a pH greater than 7 is basic. As one can see from this formula, ten times a given concentration of hydrogen ions means one unit lower in terms of pH value (higher acidity), and vice versa.


The pH value of a solution varies from 0 to 14. The pH value is 0 for a very strong acid and the pH value is 14 for a very strong base. The pH value is 7 for a neutral solution. Hence A is acidic and B is basic in nature.


The concentration of hydrogen ion decreases from pH value of 0 to 14 therefore A has more hydrogen ion concentration.


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5

Mention any four limitations in harnessing wind energy on a large scale.

 6

No chemical reaction takes place when granules of a solid, A are mixed with the powder of another solid, B. However when the mixture is heated, a reaction takes place between its components. One of the products, C is a metal and settles down in the molten state while the other product, D floats over it. It was observed that the reaction is highly exothermic.

i. Based on the given information make an assumption about A and B and write a chemical equation for the chemical reaction indicating the conditions of reaction, physical state of reactants and products and thermal status of reaction.


ii. Mention any two types of reactions under which above chemical reaction can be classified.

 8

Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells but different number of electrons in their outermost shell. It was found that elements A and G combine to form an ionic compound. This compound is added in a small amount to almost all vegetable dishes during cooking. Oxides of elements A and B are basic in nature while those of E and F are acidic. The oxide of D is almost neutral. Based on the above information answer the following questions:

i. To which group or period of the periodic table do the listed elements belong?


ii. What would be the nature of compound formed by a combination of elements B and F?


iii. Which two of these elements could definitely be metals?


iv. Which one of the eight elements is most likely to be found in gaseous state at room temperature?


v. If the number of electrons in the outermost shell of elements C and G be 3 and 7 respectively, write the formula of the compound formed by the combination of C and G.

 9

i. Explain why the rate of photosynthesis in plants is low both at lower and higher temperatures.

ii. Is green light most or least useful in photosynthesis and why?


OR


Why does absorption of digested food occur mainly in the small intestine?