Thursday, August 2, 2012


ASSIGNMENT : FIRST TERM (2012-2013)                 X SUBJECT   : CHEMISTRY
A. Very short answer questions: (1 mark each) (1x 14= 14 marks)
1. What are reactants ?
2. What are products ?
3. What is the term used for symbolic representation of a chemical reaction ?
4. What does the + sign between the reactants indicate ?
5. How is the salt solution in water indicated in a chemical reaction /
6. Aluminium burns in chlorine to form aluminum chloride. Write a balanced equation for this reaction ?
7. Balance the following equation and add the state symbols :
Zn(s) + 2HCl(aq) ZnCl2 + H2
8. Name the following reaction.
9. Aluminium metal displaces iron from ferric oxide (Fe2O2) giving aluminium oxide and iron. Which is more reactive, aluminium or iron ?
10. Identify from the following reaction : H2S + Cl2 2HCl + S
a. Component oxidized
b. Oxidizing agent
11. Give one example of a redox reaction which is also a combination reaction.
12. Which atom is reduced on burning an element in air.
13. When SO2 gas is passed through saturated solution of H2S, the following reaction occurs
SO2 + 2H2S 2 H2O + 3S
In this reaction, which substance is oxidized and which one is reduced.
14. In the following reaction between lead sulphide and hydrogen peroxide
PbS(s) + 4H2O(aq) PbSO4(s) + 4H2O(l)
a. Which substance is reduced ?
b. Which substance is oxidized ?
B. Short answer questions: (2 marks each) (2x4=8)
1. Write a chemical equation for each of the following reactions :
a. Zinc metal reacts with aqueous solution of hydrochloric acid to form zinc chloride solution and hydrogen gas.
b. When solid mercury (II) oxide is heated, liquid mercury and oxygen gas are produced.
2. H2 + O H2O is a balanced chemical equation. It is considered to be incorrect. Why? 3. Write balance chemical equations to represent the following statements :
a. Carbon (coke) burns in air to form carbon dioxide gas.
b. A piece of sodium metal on putting in water forms caustic soda and hydrogen gas.
3. Write the balanced chemical equations for the following chemical reactions :
a. Aqueous solutions of sulphuric acid and sodium hydroxide react to form aqueous sodium sulphate and water.
b. Phosphorus burns in chlorine gas to form phosphorus penta chloride.
4. Magnesium is more reactive than copper or iron but iron is more reactive than copper.
a. A solution of magnesium sulphate is put into a copper pot.
b. A solution of copper sulphate is put into a iron pot.
c. A solution of magnesium sulphate is put into a iron pot.
Which of the above pots will get damaged? Why? What is this reaction called?
C. Short answer questions: (3 marks each)(3x 4= 12)                  
1. What are the three essentials of a chemical equation ?
2. Explain the term reduction with examples.
3.A colourless lead salt, when heated, produces a yellow residue and brown fumes.
a. Name the lead salt.
b. Name the brown fumes.
c. Write a chemical equation of the reaction involved.
4. When a green iron salt is heated strongly, its colour finally changes to black and colour of burning  sulphur is given out.
a. Name the iron salt.
b. Name  the type of reaction that takes place during the heating of iron salt.
c. Write a chemical equation for the reaction involved.
D. Balance the following skeleton equation by hit and trial method : (2x6=12)
a. C2H4 + O2 CO2 +H2O
b. C2H2 + O2 CO2 +H2O
c. CH4 + O2 CO2 +H2O
d. Al2(SO4)3 + NaOH Al(OH)3  + Na2SO4
e. Cu2S + O2 Cu2O +S2O
f.  AlN + H2O Al(OH)3  + NH3
E Define: (1x9=9)
1. Rancidity      2. Combination reactions  3. Decomposition reactions 4. Double displacement reaction  5. Displacement reaction   6. Redox reaction     7. Corrosion  8. Oxidising agent   9. Reducing agent

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