(a)(i) Define the term Hygroscopic: Hygroscopic substance – is defined as a substance which absorbs moisture on exposure to the atmosphere but does not form solution or change state.
(ii) Give two differences between a physical and a chemical change:

Physical Change	Chemical Change
No new substance formed	New substance formed
Change is easily reversibl	Change is not easily reversible
Heat change is not usually involved	Heat is usually given out or absorbed/it involves heat
No change in mass of substance involved	Change in mass of substance involved

(iii) Using the kinetic theory of gases, explain briefly the Charles' law: At constant pressure, when the temperature of a gas is increased, the molecules gain more kinetic energy and move faster. The distance between the molecule increases resulting in increased in the volume of the gas.

(b)(i) Arrange the following compounds in order of increasing boiling points:
CO\(_2\), CS\(_2\), NaH
CO\(_2\) — Weak vander Waal's forces.
CS\(_2\) — Stronger vander Waals's forces.
NaH — With ionic forces stronger than vander Waal's forces.
(ii) Write a balanced equation to illustrate the reaction of chlorine gas with cold dilute sodium hydroxide.
Cl\(_{2(g)}\) + 2NaOH\(_{(aq)}\) \(\to\) NaCl\(_{(aq)}\) ; NaCI\(_{(g)}\) + H\(_2\)O\(_{(l)}\)

(c) In a certain reaction, 15.0g of impure magnesium sample reacted with excess hydrochloric acid liberating 8.6dm\(^3\) of hydrogen gas at s.t.p
(I) Write a balance equation for the reaction.

Mg\(_{(g)}\) 2HCI\(_{(aq)}\) ---> MgCl\(_{2(ag)}\) + H\(_{2(g)}\).

(ii) Calculate the: I. Mass of pure magnesium in the sample
Mg + 2HCI \(\to\) MgCl\(_2\) + H\(_2\)
1 mole H\(_2\) = 1 moles mg
n(H\(_2\)) = \(\frac{8.6}{ 22.4}\)
= 0.384moles.
Hence, number of moles of Mg = 0.384moles
Mass of Mg = mole x molar mass
= 0.384 x 24
= 9.21g.
II. % purity = \(\frac{\text{Mass of pure Mg}}{\text{Mass of impure Mg}}\) x 100
Mg = \(\frac{9.21}{15.0}\) x 100
= 61.4%
Ill. From the equation;
Moles of cl\(^{-2}\) = 2 x moles of Mg
= 2 x 0.384
= 0.768 moles
No of Cl\(^{-}\) produced x N\(_A\)
= 0.768 x 6.02 x 10\(^{23}\)
= 4.62 x 10\(^{23}\) Cl\(^{-}\)