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KCSE CLUSTER TEST 14

Chemistry Paper 3

1.

i)A Complete table............................................................................................1mk

(Tied to temperature readings column) -Incomplete table with three temperature values.........................................1mk

-Incomplete table with less than three temperature readings....................0mks

-Penalize ½mk for unrealistic temperature values i.e <100c and greater 1000c.

B Decimal (tied to temperature readings)......................................................1mk.

Accept whole numbers readings or one d.p. Used consistently (1st decimal should be ‘’0’’or‘’5’’)

C Accuracy: (Tied to temperature in the 1st experiment).................................1mk

-Compare the candidate 1st temperature reading with the school value (teacher’s value). -If within + 2 of the school value...........................................................1mk Otherwise penalize fully (i.e award 0 mk).

D Trend ..........................................................................................................1mk

-Accept decreasing temperature readings for 1mk, otherwise penalize fully.

E Calculate for solubilities in column three..................................................2mks

-A award ½ mk for each correct solubility.

ii) GRAPH.....................................................................................................3mks

a) Labelling of axes........................................................................................½mk

Penalties -Inverted axes. -Wrong units.

-Not labelling on one axis NB: Penalize fully for any of the above.

b) Scale............................................................................................................½mk

Conditions. -Correct intervals. -Area covered by plots should be a half or more of the grid provided.

-To accommodate all points even those not plotted. NB: Penalize fully for any condition not met. c) Plotting..........................................................................................................1mk

Conditions. -Three –four points plotted correctly.........................................................1mk.

-Only 2 points correctly plotted................................................................½mk

-Less than 2 points plotted.......................................................................0mk

NB :(i) Accept even if axes are inverted. d) Shape of the graph....................................................................................1mk

-Accept a smooth curve passing through at least 3 points.

(iii) -Showing on the graph..............................................................................½mk

-Correct reading.......................................................................................½mk

e) Table II a) Complete table................................................................................1mk

Conditions: i. Complete table with 3 titrations done.............................................1mk

ii. Incomplete table with 2 titrations done.........................................½mk

iii. Incomplete table with only 1 titrations done....................................0mk

Penalties. -Wrong arithmetic. -Inverted table.

-Burette reading beyond 50 cm3 unless explained.

-Unrealistic titres i.e. too small (below 1.0 cm3 or too high over 100cm3)

-Penalize ½mk for each to a maximum of ½ mk i.e Penalize ½ mk once.

b) Use of Decimals..........................................................................1mk

(Tied to 1st and 2nd rows only)

Conditions.

i. Accept either 1 or 2 d.p used otherwise penalise fully.

ii. If 2 d.p are used the 2nd must be a ‘0’ or ‘5’ otherwise penalize fully.

iii. Accept inconsistency of zero as initial burette reading i.e 00.0

c) Accuracy.......................................................................................1mk

Compare the candidate titre values with the S.V tick the chosen value where it earns a mark. (S.V is the teachers Average titre value)

i. It at least one value is within ± 0.1 cm3of S.V ........................1mk

ii. If one value is within ±0.2cm3 of S.V.......................................½mk

iii. If no value is within ± 0.2cm3 of the S.V..................................0 mk.

Compare the S.V with the worked out CORRECT TITRE and award accordingly.

d) Principle of Averaging................................................................1mk

Conditions i. If 3 consistent values are averaged............................................1mk

ii. If 3 titrations are done but only 2 consistent and are averaged...1mk

iii. If only 2 titrations are done and are consistent and are averaged.1mk

iv. If 3 are possible but only 2 are averaged.......................................0mk

v. If 3 titrations are done and inconsistent and averaged...................0mk.

Penalties

i. Penalise ½ mk for wrong arithmetic if the error is outside ±2 units in the 2nd d.p.

ii. Penalise ½mk if no working is shown but the answer is correct.

iii. If no working is shown but answer given is wrong penalise fully.

iv. Accept rounding off of answer to 2 d.p otherwise penalise ½mk for rounding off to d.p or whole number

. NOTE:

i). Accept answer if it works out exactly to 1 d.p or to a whole number.

ii) Section (i) must be marked for the mark for averaging to be awarded in table 1.

e) Final Accuracy.......................................................................................1mk

Compare the candidates CORRECT average titre with the S.V. i. If within ±0.1cm3 of the S.V.....................................................1mk

ii. If within±0.2cm3 of the S.V ......................................................½mk

iii. If beyond ±0.2cm3 of the S.V.................................................0mk

NOTE: i) Incase there was wrong arithmetic in the table, use the correct value in averaging for the final answer.

ii) Where there are two possible average titres use the value which gives the candidates maximum credit.

iii)If wrong values are averaged, pick the correct values(if any)following the principles of averaging, and averaged and award accordingly.

CALCULATIONS
ii) I Already as principle of average mark on the table.

Conditions and penalties.
i. Penalize ½ mk for wrong units otherwise units ignore if units are missing, but if given must be correct for all parts.

ii. Answers must be given correct to 4 d.p or more unless it works out exactly in all parts.

iii. Penalize fully for any strange figure

21 marks

2.

11 marks

3.

8 marks

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