MEMORANDUM GRADE 11. PHYSICAL SCIENCES: CHEMISTRY Paper 2

Transcription

1 MEMORANDUM GRADE 11 PHYSICAL SCIENCES: CHEMISTRY Paper 2 MARKS: 150 TIME: 3 hours

2 Learning Outcomes and Assessment Standards LO1 LO2 LO3 AS : Plan and conduct a scientific investigation to collect data systematically with regard to accuracy, reliability and the need to control variables. AS : Seek patterns and trends, represent them in different forms to draw conclusions, and formulate simple generalisations. AS : Apply known problemsolving strategies to solve multi-step problems. AS : Define and discuss basic prescribed scientific knowledge. AS : Express and explain prescribed scientific theories, models and laws by indicating the relationship between different facts and concepts in own words. AS : Apply scientific knowledge in everyday life contexts. AS : Research, discuss, compare and evaluate scientific and indigenous knowledge claims by indicating the correlation among them, and explain the acceptance of different claims. AS : Identify ethical and moral issues related to the development of science and technology and evaluate the impact (pros and cons) of the relationship from a personal viewpoint. MEMORANDUM: Maskew Miller Longman, Focus on Physical Sciences Grade 11 Chemistry: Paper 2 Page 2 of 10

3 Section A Question 1: One-word items 1.1 Lewis acid [11.2.1] (1) 1.2 real gases [11.2.1] (1) 1.3 polymerisation [11.2.1] (1) 1.4 empirical formula [11.2.1] (1) 1.5 stratosphere [11.2.1] (1) [5] Question 2: False items 2.1 If the bonds in a molecule are polar, the molecule could be either polar or non-polar. [11.2.3] (2) 2.2 The volume of all gases at standard temperature and pressure is 22,4 dm 3. [11.2.3] (2) 2.3 A chemical bond is the net electrostatic force that two atoms sharing electrons exert on each other. [11.2.3] (2) 2.4 Hydrogenation of vegetable oils leads to the formation of margarine. [11.2.3] (2) 2.5 The auroras are found in the ionosphere. [11.2.3] (2) [10] Question 3: Multiple choice 3.1 C [11.2.2] (2) 3.2 D [11.2.2] (2) 3.3 B [11.2.1] (2) 3.4 B [11.2.2] (2) 3.5 C [11.2.3] (2) [10] Total Section A: 25 MEMORANDUM: Maskew Miller Longman, Focus on Physical Sciences Grade 11 Chemistry: Paper 2 Page 3 of 10

4 Section B Question What is the relationship between volume and temperature of a given mass of gas that is kept at constant pressure? [11.1.1] (2) 4.2 The volume of a gas is directly proportional to the absolute temperature when is kept at constant pressure. [11.1.1] (2) 4.3 Graph of volume versus temperature Criteria for the graph 1 0 Suitable heading Axes correctly labelled with units Correct scale on both axes Points correctly plotted Straight line graph drawn through points Total out of 5 [11.1.2] (5) 4.4 pressure [11.1.1] (1) MEMORANDUM: Maskew Miller Longman, Focus on Physical Sciences Grade 11 Chemistry: Paper 2 Page 4 of 10

5 4.5 Gradients are equal y x = x y 24,6/x = /100 x = 273,33 Temperature = 273,33 C Absolute zero temperature [11.1.3] (4) 4.6 Gradient = = V T Question pv = nrt pv = nrt V 0,3 8, = = 103,3 kpa [11.1.3] (6) [20] [11.2.2] (2) [11.2.2] (2) [11.2.2] (3) MEMORANDUM: Maskew Miller Longman, Focus on Physical Sciences Grade 11 Chemistry: Paper 2 Page 5 of 10

6 5.3 n(h) = 6,67 = 6,67 mol 1 n(c) = 40 = 3,33 mol 12 n(o) = 53,33 = 3,33 mol 16 H : C : O 6,67 : 3,33 : 3,33 > 2 : 1 : 1 > H 2 C 1 O 1 M r (H 2 CO) = 30 M r (x) = 180 = 6 30 Molecular formula = H 12 C 6 O 6 [11.1.3] (7) M r [(COOH) 2 10H 2 O] = 2(45)+10(18) = 270 % C = = 8,89 % 270 [11.1.3] (5) % H 2 O = = 66,67 % 270 Mass of water = 66,67 % of 20 g = 13,33 g [11.1.3] (4) [23] Question Concentration is the number of moles of the substance per unit volume of the solution. [11.2.1] (2) 6.2 c 1 V 1 = c 2 V 2 6 V 1 = 0,1 500 V 1 = 8,33 cm 3 [11.1.3] (5) Apparatus: burette Erlenmeyer flask pipette burette stand (4 0,5) [11.1.2] (2) MEMORANDUM: Maskew Miller Longman, Focus on Physical Sciences Grade 11 Chemistry: Paper 2 Page 6 of 10

7 6.3.2 Method: Fill burette with HCl solution. Pipette 25 cm 3 of Na 2 CO 3 into all three Erlenmeyer flasks. Add 3 drops of methyl orange indicator to each flask. Carefully add HCl solution from the burette to the carbonate solution until the colour of the indicator just changes. Note the volume of the acid added. Repeat the experiment with the other two flasks. [11.1.2] (5) 6.4 2HCl + Na 2 CO 3 2NaCl + CO 2 + H 2 O balance [11.2.2] (3) 6.5 It ionises almost completely in water. [11.2.1] (2) 6.6 Average volume of HCl = 40,66 cm 3 Average volume of Na 2 CO 3 = 25,0 cm 3 Let HCl = a and Na 2 CO 3 = b c a V a = n a c b V nb b c a V a n b = c b V b n a 0,1 40,66 1 = c b 25 2 c b = 0,08 mol dm 3 [11.1.3] (6) [25] Question H 2 (g) + O 2 (g) 2H 2 O [11.2.2] (1) From balanced equation: Volume of H 2 that reacts with 20 cm 3 O 2 = 40 cm 3 Volume of H 2 O formed = 40 cm 3 Volume of H unreacted = 10 cm 3 Volume of gases remaining = 50 cm 3 [11.1.3] (5) oxygen [11.1.2] (1) Zn(s) + 2H 2 SO 4 (aq) ZnH 2 SO 4 (aq) + H 2 (g) n(zn) = 6,45/65 mol = 0,1 mol From the balanced equation 0,1 mol Zn will produce 0,1 mol ZnSO 4. [11.1.3] (4) MEMORANDUM: Maskew Miller Longman, Focus on Physical Sciences Grade 11 Chemistry: Paper 2 Page 7 of 10

8 mol Zn produces 22,4 dm 3 hydrogen 0,1 mol Zn will produce 2,24 dm 3 hydrogen [11.1.3] (3) mol H 2 6, molecules H 2 0,1 mol H 2 will have 0,1 6, molecules H 2 = 6, molecules H 2 [11.1.3] (3) [17] Question A redox reaction is one in which there is transfer of electrons. [11.2.1] (2) 8.2 Exothermic Energy is released or H < 0 [11.2.2] (2) 8.3 Checklist Criteria for graph Correct shape products show lower energy than reactants Heat of reaction indicated correctly Activation energy indicated correctly Energy of products indicated correctly Energy of reactants indicated correctly Activated complex indicated correctly Marks [11.1.3] (6) 8.4 CO is the reducing agent. Carbon undergoes an increase in oxidation number. [11.2.2] (3) [13] MEMORANDUM: Maskew Miller Longman, Focus on Physical Sciences Grade 11 Chemistry: Paper 2 Page 8 of 10

9 Question hydrocarbons compounds containing carbon and hydrogen only saturated all bonds between carbon atoms are single bonds unsaturated there are double and triple bonds between carbon atoms [11.2.1] (3) unsaturated hydrocarbon [11.2.2] (1) The double bond between carbon atoms break and a hydrogen is attached to each carbon atom. [11.2.2] (2) substitution dehydrohalogenation/elimination hydration/addition [ ] (5) dehydration/elimination [11.2.3] (4) [15] MEMORANDUM: Maskew Miller Longman, Focus on Physical Sciences Grade 11 Chemistry: Paper 2 Page 9 of 10

10 Question oil refined into petrol and other useful chemicals coal needed for power stations for generation of electricity [11.2.1] (3) 10.2 carbon dioxide, methane, oxides of nitrogen These gases form a layer above Earth and trap heat resulting in an increase in the temperature on Earth. [11.3.2] (4) 10.3 These gases can scatter harmful radiation and prevent them from entering Earth s atmosphere. [11.3.2] (1) 10.4 Coal burning releases SO 2 into the atmosphere which dissolves in water to produce acid rain. [11.3.2] (2) 10.5 troposphere [11.2.2] (1) 10.6 catalytic converters [11.2.2] (1) [12] Total Section B: 125 Grand total: 150 MEMORANDUM: Maskew Miller Longman, Focus on Physical Sciences Grade 11 Chemistry: Paper 2 Page 10 of 10