CAMI EDUCATION PHYSICAL SCIENCES PAPER 2 MEMORANDUM CHEMISTRY - GRADE 12 AUGUST 2012

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1 CAMI EDUCATION PHYSICAL SCIENCES PAPER MEMORANDUM CHEMISTRY - GRADE 1 AUGUST 01 QUESTION Ether 1. Hidration 1.3 Galvanic cell 1.4 Saponification Hydrogen QUESTION.1 D.6 B. A.7 B.3 B.8 C.4 C.9 D.5 D.10 C 0 QUESTION D 3. A 3.3 E 3.4 B 3.5 F 3.6 C 6

2 QUESTION Methanol or Ethanol 4. Temperature of mixture is higher than boiling points of these alcohols. Therefore their fractions boiled already and have been removed. 4.3 Alcohols are flammable 4.4 Alcohols have hydrogen bonds present and the alkanes have only van der Waal s forces between molecules. Stronger intermolecular forces occur between alcohol molecules. More energy is needed to break these bonds. That leads to higher boiling points QUESTION H O / water methylbutan-1-ol 5.4 Ethanol 5.5 H SO 4 as catalyst 5.6 Reaction II QUESTION When an unsymmetrical alkene reacts with a polar molecule, the H-atom (positive part) always attaches to the carbon of the alkene that has the greater number of hydrogen substituents and the negative part of the molecule (halogen or OH group) to the carbon with the fewer number of hydrogen substituents.

3 QUESTION Heavy alkanes with straight chains are cracked at high temperature and pressure in the presence of catalysts to form lighter and simpler short chain molecules. 7. Parafin lamps / solvent / lubricant / heating / fuel 7.3 Greater demand for shorter chains (smaller molecules) that are more useful for production of other materials. 7.4 Heptane, C 7 H 16 8 (Any two of the three) 13 QUESTION Formed CO gas escapes from the beaker 8. All the CaCO 3 has reacted and no more CO gas is liberated B 8.3. A C 7

4 QUESTION Z 9. Collisions cause molecules to slow down and then lose energy Very few collisions / molecules have E > E a 9.5 Add a catalyst 9.6 Catalyst lowers the E a. More molecules and collisions will have energy higher than activation energy of the reaction. This leads to more effective collisions. QUESTION 10 [CH3OH] 10.1 K c [CO][H ] 10. CO H CH 3 OH n begin 0,36 0,64 0 n used / formed 0,1 0,4 0,1 n equilibrium 0,4 0,40 0,1 c n/v 0,4 0,4 0,1 0,1 0, 0, K c [CH3OH] [CO][H ] 0,06 (0,) (0,1) 1,5

5 10.3 Exothermic, H < Increase. According to le Chatelier s principle, the system will try to decrease the pressure if the pressure on the system is increased. If the pressure is increased the reaction which forms the least number of gas molecules will be favoured. That means the forward reaction is favoured. The [CO] and [H ] decreases and the [CH 3 OH] increases K c decreases. An increase in temperature favours the endothermic reaction, in other words favours the reverse reaction. The [CO] and [H ] increases and the [CH 3 OH] decreases. The numerator of the K c equation decreases and the denomenator increases, causing the K c value to decrease. QUESTION KNO 3 Θ Θ Θ 11. Ecell Ecathode Eanode 0,34 ( 0,5) 0,59V Ni(s) Ni + (aq) + e Cu + (aq) + e - Cu (s) Ni (s) + Cu + (aq) Ni + (aq) + Cu (s) 11.5 Mass Cu 0,395g n m M 0,395 63,5 0,006mol moles Ni dissolved : 0,006mol n M 0,37g Final mass of the Ni electrode : m Ni 0, ,7 0,37 9,90g

6 QUESTION Al O 3 1. Al O 3 has a very high melting point, lots of energy needed to achieve melting very high cost. 1.3 To save energy, only need to heat the creolite to 900 O C and not heat the Al O 3 to over 000 O C to melt. 1.4 Carbon 1.5 The carbon electrode (anode) reacts with oxygen at high temperatures and forms CO gas and burns away Al 3+ (l) + 3e - Al (s) 1.6. O - (l) O (g) + 4e Al 3+ (l) + 6O - (l) 4Al (l) + 3O (g) QUESTION Haber process 13. Nitrogen 13.3 N (g) + 3H (g) NH Ostwald process 13.5 Oxygen 13.6 NH 4 NO 3 Ammonium nitrate A process whereby dams, lakes and slow moving water receive excess nutrients that stimulate excessive plant growth Excess fertilisers are washed down into rivers during the rainy season, adding excess nutrients to the water and that leads to eutrophication Leads to excessive alge growth. As it dies it uses the oxygen in the water to decompose. The lack of oxygen causes fish and other living organisms to die. 13