SOME CHEMISTRY WAEC 1997 QUESTIONS AND ANSWERS

QUESTIONS:
1(a) List two properties of alpha particles.

(b) X is an element which exist as an

isotopic mixture containing 90% of 3919X and 10% of 4119X.

(b)i. How many neutrons are present in the isotope 4119X?

ii. Calculate the mean relative atomic mass of X. (WAEC 1997).

2(a)i. State the two main processes involved in the manufacture of oxygen from air.

ii. Name the type of chemical bonding which exists between oxygen atoms in a molecule of oxygen.

(b). What term is used to describe the relationship between oxygen and ozone (WAEC 1997).

SOLUTIONS:
1(a). Alpha particles exert high powerful ionising effect upon any gas through which they pass.

ii. Alpha partcles are positively charged.
(b). No. Of neutrons in 4119X is 41- 19 = 22 neutrons.
ii. 90% of 3919X + 10% of 4119X = 90/100 X 39 + 10/100 X 41
                           = 35.1 + 4.1
   = 39.2 is the relative atomic mass


2(a)I. Liquefaction of air and fractional distillation of liquid air

ii. Covalent bonding.
(b). Ozone is an alotrope of oxygen.


QUESTIONS:
3(a)I. What is meant by cracking of petroleum fractions?

ii. Write an equation for the laboratory preparation of ethene and ethanol.

iii. Give one chemical test to distinguish between ethane and ethene.

(b)I. Name the class of carbohydrates to which starch and cellulose belongs.

ii. What process is used for isolating ethanol from the other products of fermentation of sugar?

iii. Name the organic ptoduct of the reaction between ethanol and sodium

(iv). Write the structural formula of 2- chloroethanol.

(C). State the reason why;

(I). Benzene produces more so than ethene on burning in excess air.

ii. Ethanoic acid has a higher boiling point than methanoic acid;

iii. Sodium chloride is used during the manufacture of soap.

(d) Give one use of; (I) ETHYNE   (ii) coal.  (iii) carbon black.
(WAEC 1997).

SOLUTIONS:
3(a)I. Cracking is the conversation of surplus supply of less desirable fraction such as kerosene and gas oil into petrol.

ii. C2H5OH + H2SO4 + H2 ----------- C2H4 (ethene)

iii. When ethane and ethene are separately passed through bromine water, ethane will not react with bromine water but ethene decolourises the purple colour of the bromine water.

(b)i. Polysaccharide.    ii. Fractional distillation
iii. Sodium ethoxide.   
iv.  2- chloro ethanol.  (Cl - CH2 - CH2 - OH)

(C)I. Benzene produces more soot than ethene due to the high carbon content of the former

ii. Because of high molecular weight and high carbon content in ethanoic acid than methanoic acid.

iii. The sodium chloride used during the manufacture of soap is to decrease the solubility of the soap so that it separates out as hard cake.

(d)I. Ethyne- used in the synthesis of neoprene rubber

(d)ii. Coal- used mainly as a fuel

(d)iii. Carbon black- used in manufacturing Tyre.