Page 274 - Chemistry

Table II
Marking points
Complete table (T) ………. 2 ½ mk
Award 1.2 mk for each correct to up to 3 s.f otherwise award 0
Experiment Time (sec) 1 / time
1
2
3
4
5
CT = 2 ½
DP = ½
AC = ½
Tr = ½
4
Decimal point (dp)……………………… ( ½ mk)
All values of time (t to be whole number or to 1d.p or 2d.p consistently otherwise award 0mk.

Accuracy (AC)………… ½ mk
Consider time for experiment only if 3 sec of school value (SV) award ½ mk if beyond 0mk.

Trend (Tr)…………… ½ mk
Values of t to be increasing if otherwise 0mk
Summary
Complete table CT = 2 ½
Decimal point DP = ½
Accuracy Ac = ½
Trend Tr = ½
4mk
(a) Graph
Labeled axes with correct units = ½ mk
Scale to cover ½ or more of space = ½
Plotting done correctly = 1
Straight line through 3 point = 1
3mks

(b) Straight line graph
Increase in concentration; there are more collisions leading to increase in rate of reaction
(c) To read correct value of 1/t from graph
T=1/t ½ mk = ans. ½ mk
Question 3
Observation Inference
(a) (i) Dissolves colourless solution ½ mk Coloured ions absent, polar substance ½ mk
2+
3+
(ii) White ppt forms ½ mk Al Pb 2+ , Zn present
,
soluble in excess ½ mk 3 ions 1mk
2 ions ½ mk
1 ion 0mk
2+
3+
2+
(iii) No white forms ½ mk Al or Pb present ½ each if Zn absent ½ mk
Insoluble in excess ½ mk
3+
2+
(iv) No white ppt forms 1mk Pb absent pr Al present 1 for any
2-
2-
2-
(v) White ppt forms 1mk Cl-, SO 4, SO 3, SO 3
4 ions 1mk
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