(a)(i) Sketch a graphical representation of Charles’ law.
(ii) Calculate the volume of oxygen that would be required for the complete combustion of 2.5 moles of ethanol at s.t.p. [molar volume at s.t.p. = 22.4 dm\(^3\)]
(b)(i) State the collision theory of reaction rates.
(ii) Using the collision theory, explain briefly how temperature can affect the rate of a chemical reaction.
(c)(i) Define esterification.
(ii) Give two uses of alkanoates.
(iii) Give the products of the alkaline hydrolysis of ethyl ethanoate.
(d) A tin coated plate and a galvanized plate were exposed for the same length of time.
(i) Which of the two plates corrodes faster
(ii) Explain briefly your answer in 2(d)(i)
Explanation
(a)(i) Sketch of Graphical Representation of Charles' Law: Volume (cm\(^3\))
(ii) Volume of O\(_{2(g)}\) required for complete combustion of 2.5 moles of ethanol at s.t.p.
C\(_{2}\)H\(_{5}\)OH\(_{(aq)}\) + 3O2\(_{2}\) -> 3H\(_{2}\)O + 2CO\(_{2(g)}\)
1 mole of ethanol = 3 x 22.4 dm\(^{2}\). of O\(_{2(g)}\)
.-. 2.5 moles of ethanol = 3 x 22.4 dm\(^{3}\) x 2.5
= 168.0 dm\(^{3}\).
(b)(i) Collision theory of reactants rates states that atoms/molecules/ions/particles/reactions involved in a chemical reaction must collide with effective collision before reaction can take place.
(ii) Using collision theory to explain effect of temperature on the rate of a chemical reaction: Increase in temperature makes the reacting molecules to gain kinetic energy and move faster. Where the temperature decreases, the reacting molecules lose kinetice energy and move slower. Frequency of collision and effective collision increase or decrease, therefore rate of reaction increases or decreases.
(c)(i) Esterification is the reaction between an alkanol and alkanoic acid to produce an Alkanoate (ester) and water in the presence of a mineral acid.
(ii) Two uses of alkanoates are: (1) Used in perfumes/cosmetics. (2) Used in artificial flavouring for foods. (3) Used in production of soap. (4) Used as plasticizers. (Any 2)
(iii) Products of the alkaline hydrolysis of ethyl ethanoate are: ethanol (C\(_{2}\)H\(_{5}\)OH) and sodium ethanoate (CH\(_{3}\)COONa) or potassium ethanoate CH\(_{3}\)COOK.
(d)(i) Tin-coated plate corrodes faster.
(ii) Zinc is more reactive than tin, higher in the electrochemical series than tin. When the tin coated plate is exposed, the plate goes into solution and corrodes. In zinc coated (galvanized) plate, it is zinc that dissolves and corrodes hence protecting the plate better and zinc coated plate does not corrode.