Thursday, September 8, 2011

10th SA-1-Acid Base and Salt CBSE TEST PAPER

1. What will be the action of the following substances on litmus paper?

Dry HCl gas, Moistened NH3 gas, Lemon juice, carbonated soft drink, Curd, Soap solution

2. Name the acid present in ant sting and give its chemical formula. Also give the common method to get relief from the discomfort caused by the ant sting.

3. What happens when nitric acid is added to egg shell?

4. How would you distinguish between baking powder and washing soda by heating?

5. Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B and C.

6. In one of the industrial processes used for manufacture of sodium hydroxide, a gas X is formed as by product. The gas X reacts with lime water to give a compound Y which is used as a bleaching agent in chemical industry. Identify X and Y giving the chemical equation of the reactions involved

7. When zinc metal is treated with a dilute solution of a strong acid, a gas is evolved, which is utilised in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed

8. For making cake, baking powder is taken. If at home your mother uses baking soda instead of baking powder in cake, (a) how will it affect the taste of the cake and why? (b) how can baking soda be converted into baking powder? (c) what is the role of tartaric acid added to baking soda?

9. A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identity X, Y, G and Z

10. A dry pellet of a common base B, when kept in open absorbs moisture and turns sticky. The compound is also a by–product of chloralkali process. Identify B. What type of reaction occurs when B is treated with an acidic oxide? Write a balanced chemical equation for one such solution.

11. A sulphate salt of Group 2 element of the Periodic Table is a white, soft substance, which can be moulded into different shapes by making its dough. When this compound is left in open for some time, it becomes a solid mass and cannot be used for moulding purposes. Identify the sulphate salt and why does it show such a behavior? Give the reaction involved.

Solution :
1. Substance                          Action on Litmus paper

Dry HCl gas                                  No change

Moistened NH3 gas                      Turns red to blue

Lemon juice                                  Turns blue to red

Carbonated soft drink                   Turns blue to red

Curd                                              Turns blue to red

Soap solution                                Turns red to blue

2. The acid present in ant sting is methanoic acid (formic acid). The chemical formula is HCOOH. To get relief one should apply any available basic salt e.g., baking soda (NaHCO3) on it.

3. Egg shells contain calcium carbonate. When nitric acid is added to it, carbon dioxide gas is evolved. The reaction can be given as

CaCO3 + 2HNO3 --------> Ca (NO3)2 + H2O + CO2

4. The chemical formula of baking powder is sodium hydrogencarbonate (NaHCO3). Whereas, that of washing soda is sodium carbonate (Na2CO3.10H2O) Sodium hydrogencarbonate on heating gives CO2 gas which will turn lime water milky whereas no such gas is obtained from sodium carbonate.

2NaHCO3 ---He---at-→ Na2CO3 + H2O + CO2

Na2CO3.10H2O ----He---at→ Na2CO3 + 10H2O

5. Baking powder (NaHCO3), salt A is commonly used in bakery products. On heating it forms sodium carbonate (Na2CO3), B and CO2 gas, C is evolved. When CO2 gas is passed through lime water it forms calcium carbonate (CaCO3), which is slightly soluble in water making it milky.

A — NaHCO3 B — Na2CO3 C — CO2 gas

6. In the manufacture of sodium hydroxide, hydrogen gas and chlorine gas (X) are formed as by–products. When chlorine gas (X) reacts with lime water, it forms calcium oxychloride (bleaching powder) Y. The reactions are

2NaCl (aq) + 2H2O(l) ------> 2NaOH (aq) + Cl2 (g) + H2(g) here, X---------> Cl2 (Chlorine gas)

Ca (OH)2 (s) + Cl2 (g) > CaOCl2 (s) + H2O here, Y —> Calcium oxychloride (bleaching powder)

7. When zinc reacts with dilute solution of strong acid, it forms salt and hydrogen gas is evolved.

Zn + 2HCl ----> ZnCl2 + H2

When a burning splinter is brought near the mouth of the test tube, the gas burns with a pop sound.

8. (a) Baking soda is sodium hydrogencarbonate. On heating, it is converted into sodium carbonate which is bitter to taste

2NaHCO3 ⎯⎯He⎯at⎯→ Na2CO3 + H2O + CO2

(b) Baking soda can be converted into baking powder by the addition of appropriate amount of tartaric acid to it.

(c) The role of tartaric acid is to neutralise sodium carbonate and cake will not taste bitter.

9. The gas evolved at anode during electrolysis of brine is chlorine (G) When chlorine gas is passed through dry Ca(OH)2 (Y) produces bleaching powder (Z) used for disinfecting drinking water.

Ca(OH)2 + Cl2 ------> CaOCl2 + H2O

Since Y and Z are calcium salts, therefore X is also a calcium salt and is calcium carbonate.

CaCO3 + 2HCl -------> CaCl2 + CO2 + H2O Ca(OH)2 + CO2 ---------à CaCO3 + H2O

10. Sodium hydroxide (NaOH) is a commonly used base and is hygroscopic, that is, it absorbs moisture from the atmosphere and becomes sticky.

The acidic oxides react with base to give salt and water. The reaction between NaOH and CO2 can be given as 2 NaOH + CO2 ---------> Na2CO3 + H2O

11. The substance which is used for making different shapes is Plaster of Paris. Its chemical name is calcium sulphate hemihydrates (CaSO4 . ½H2O). The two formula unit of CaSO4 share one molecule of water. As a result, it is soft.

When it is left open for some time, it absorbs moisture from the atmosphere and forms gypsum, which is a hard solid mass.

CaSO4 . ½H2O + 3/2H2O ---------> CaSO4. 2H2O

Plaster of Paris Gypsum

(Soft) (Hard mass) (Sulphate salt)

No comments:

Post a Comment