(a) (i) State the important points put forward in Dalton’s atomic theory.
(ii) How does the theory explain the law of multiple proportion?
(b) (i) Name three commercially useful products that may be obtained by chemical transformation of vegetable oils.
(ii) With the aid of equations, describe the chemical reaction involved in the transformations stated in (b)(i).
(c) Certain properties of Beryllium (Be) and its compounds differ from those of Magnesium (Mg) and its compounds, but rather resembles those of Aluminium and its compounds. Explain briefly why this is so.
(d) Write balanced equation for the reaction between iodine and aqueous sodium trioxothiosulphate(VI).
(a)(i) Dalton's atomic theory: matter is made of tiny indivisible particles called atoms; atoms of the same element are identical in mass and properties, and differ from those of other elements; atoms combine in simple whole-number ratios to form compounds; atoms are neither created nor destroyed in a chemical reaction (which is only a rearrangement of atoms).
(ii) Because whole atoms combine in simple whole-number ratios, when two elements form more than one compound the masses of one element that combine with a fixed mass of the other must be in a simple whole-number ratio, which is the law of multiple proportions.
(b)(i) Three products: margarine (by hydrogenation), soap (by saponification), and glycerol (by hydrolysis/saponification).
(ii)
- Hydrogenation (to margarine): unsaturated oil \(+ H_2 \xrightarrow{Ni} \) hardened (saturated) fat.
- Saponification (to soap): \((C_{17}H_{35}COO)_3C_3H_5 + 3NaOH \rightarrow 3C_{17}H_{35}COONa + C_3H_5(OH)_3\)
- Hydrolysis (to glycerol): \((C_{17}H_{35}COO)_3C_3H_5 + 3H_2O \rightarrow 3C_{17}H_{35}COOH + C_3H_5(OH)_3\)
(c) This is a diagonal relationship: beryllium and aluminium lie diagonally in the periodic table and have similar charge-to-radius ratios (similar polarizing power and electronegativity), so their properties resemble each other rather than those of magnesium.
(d) \(I_2 + 2Na_2S_2O_3 \rightarrow 2NaI + Na_2S_4O_6\)
(a)(i) Dalton's atomic theory: matter is made of tiny indivisible particles called atoms; atoms of the same element are identical in mass and properties, and differ from those of other elements; atoms combine in simple whole-number ratios to form compounds; atoms are neither created nor destroyed in a chemical reaction (which is only a rearrangement of atoms).
(ii) Because whole atoms combine in simple whole-number ratios, when two elements form more than one compound the masses of one element that combine with a fixed mass of the other must be in a simple whole-number ratio, which is the law of multiple proportions.
(b)(i) Three products: margarine (by hydrogenation), soap (by saponification), and glycerol (by hydrolysis/saponification).
(ii)
- Hydrogenation (to margarine): unsaturated oil \(+ H_2 \xrightarrow{Ni} \) hardened (saturated) fat.
- Saponification (to soap): \((C_{17}H_{35}COO)_3C_3H_5 + 3NaOH \rightarrow 3C_{17}H_{35}COONa + C_3H_5(OH)_3\)
- Hydrolysis (to glycerol): \((C_{17}H_{35}COO)_3C_3H_5 + 3H_2O \rightarrow 3C_{17}H_{35}COOH + C_3H_5(OH)_3\)
(c) This is a diagonal relationship: beryllium and aluminium lie diagonally in the periodic table and have similar charge-to-radius ratios (similar polarizing power and electronegativity), so their properties resemble each other rather than those of magnesium.
(d) \(I_2 + 2Na_2S_2O_3 \rightarrow 2NaI + Na_2S_4O_6\)
