(a) Explain briefly why \(_2^4He\) has a stable electron configuration compared to \(_4^9Be\)
(b) Consider the following elements: 1H and 3Li.
(i) State the number of electrons that an atom of each element would have after forming an ionic bond.
(ii) Give a reason for each of your answers stated in (b)(i).
(c) State two factors that should be considered when siting a chemical industry.
(d) State two advantages of using a catalyst instead of high temperatures in chemical reactions.
(e) Turpentine burns in chlorine according to the following equation:
C\(_{10}\)H\(_{16}\)\(_{(I)}\) + 8Cl\(_{2(g)}\) \(\to\) 10C\(_{(s)}\) + 16HCl\(_{(g)}\)
Calculate the mass of turpentine that would completely burn in 21.3 g of chlorine.
[Molar mass of chlorine = 71 gmol\(^{-1}\); Molar mass of Turpentine = 136 gmol\(^{-1}\)]
(f) What is cracking?
(g) State two factors that may influence the value of electron affinity.
(h) What are carbohydrates?
(i) State two differences between a simple sugar and starch.
(j) Write an equation to show the dissociation of each of the following acids:
(i) H\(_2\)CO\(_3\);
(ii) CH\(_3\)COOH.
Explanation
(a) \(_2^4He\) has its outermost / Valence shell fully filled with electrons / has maximum number of electrons in its outermost shell / duplet thus more stable whereas \(_4^9Be\) has incomplete filled outermost / valence shell hence less stable.
(b) (i) 1H - 2 electrons / zero
3Li - 2 electrons
(ii) 1H - it accepts one electron / donates one electron
3Li - it loses an electron to have a duplet shell
(c) - nearness to raw material / feed stock
- nearness to markets
- labour supply
- transportation
- availability of power supply
- government policy
- away from residential areas
- storage facilities for raw materials
- source of water supply
- conducive climate
(d) - saves money / the plant does not have to operate for long to produce
- reduces energy / reaction proceeds at a much lower temperature
- no undesirable products are formed / catalyst is specific in action
(e) From the equation:
8 moles of Cl\(_2\) reacts with 1 mole turpentine
1 mole of Cl\(_2\) = 71 g
8 moles = 8 x 71
= 568 g
\(\frac{21.3}{568}\)g will react with 21.3 x 136
= 5.1 g
OR
8 moles of Cl\(_2\) reacts with 1 mole turpentine
8 moles of Cl\(_2\) = 8 x 71 = 568 g
21.3 g of Cl\(_2\) = \(\frac{136}{71 \times 8}\) x 21.3
= 5.1 g
OR
Mole of Cl\(_2\) = \(\frac{21.3}{71}\) = 0.3 mole
8 moles Cl\(_2\) \(\to\) 136 g C\(_{10}\)H\(_{16}\)
0.3 mole Cl\(_2 \) = \(\frac{136}{8}\) x 0.3
= 5.1 g
(f) Cracking is the breaking down of long chain hydrocarbons into smaller molecules
by the action of heat and / or in the presence of a catalyst.
(g) - nuclear charge
- atomic size
- electron configuration
(h) Carbohydrates are molecules / organic compounds consisting of carbon, hydrogen and oxygen atoms usually with hydrogen and oxygen atoms in the ratio of 2:1.
(i)
|
Sugar |
Starch |
|
- monosaccharides / low molar |
- polysaccharides / high molar mass |
|
- single units of specific molecules |
- long chains of single sugar molecule/ |
|
- general formula C\(_x\)H\(_{2y}\)O\(_{y}\) |
- general formula (C\(_6\)H\(_{10}\)O\(_5\))n |
|
- crystalline |
- amorphous / non crystalline |
|
- soluble in water |
- insoluble in water |
(j) (i) H\(_2\)CO\(_{3(aq)}\) \(\to\) H\(^+\)\(_{(aq)}\) + HCO\(_{3(aq)}\)\(^{-}\)
OR
H\(_2\)CO\(_{3(aq)}\) \(\to\) 2H\(^{+}\)\(_{ (aq) }\) + CO\(_{3(aq)}^{2-}\)
OR
H\(_2\)CO\(_{3 (aq)}\) + H\(_2\)O\(_{(l)}\) \(\to\) H\(_3\)O\(^+\)\(_{(aq)}\) + HCO\(_{3 (aq)}^-\)
H\(_2\)CO\(_{3 (aq)}\) + 2H\(_2\)O\(_{(l)}\) \(\to\) 2H\(_3\)O\(^+\)\(_{(aq)}\) + CO\(_{3 (aq)}^{2+}\)
(ii) CH\(_3\)COOH\(_{(aq)}\) + H\(_2\)O\(_{(l)}\) \(\to\) CH\(_3\)COO\(^-_{(aq)}\) + H\(_{3}\)O\(^{+}\)\(_{(aq)}\)
OR
CH\(_3\)COOH\(_{(aq)}\) \(\to\) CH\(_3\)COO\(^-_{(aq)}\) + H\(^+_{(aq)}\)