Concentrations # of drops # of drops # of drops Stock Solution Stock Solution Re
ID: 878678 • Letter: C
Question
Concentrations
# of drops
# of drops
# of drops
Stock Solution
Stock Solution
Reaction (after mixing in well)
Reaction (after mixing in well)
Reaction Time
(seconds)
Reaction
Rate
(sec-1)
Well #
HCl
H2O
Na2S2O3
HCl
Na2S2O3
HCl
Na2S2O3
Trial 1
Trial 2
Average
C1, D1
12
0
8
1M
0.3M
Yellow, odor
Yellow, odor
36
34
35
0.03
C2, D2
6
6
8
1M
0.3M
Yellow, odor
Yellow, odor
42
41
42.5
0.02
C3, D3
4
8
8
1M
0.3M
Yellow, odor
Yellow, odor
42
44
43
0.02
Concentrations
# of drops
# of drops
# of drops
Stock Solution
Stock Solution
Reaction (after mixing in well)
Reaction (after mixing in well)
Reaction Time
(seconds)
Reaction
Rate
(sec-1)
Well #
HCl
H2O
Na2S2O3
HCl
Na2S2O3
HCl
Na2S2O3
Trial 1
Trial 2
Average
C4, D4
8
0
12
1M
0.3M
Yellow, odor
Yellow, odor
21
23
22
0.05
C5, D5
8
6
6
1M
0.3M
Yellow, odor
Yellow, odor
47
50
48.5
0.02
C6, D6
8
8
4
1M
0.3M
Yellow, odor
Yellow, odor
80
90
85
0.01
Determine the Reaction Order for HCl using calculations described in the Background section. Show your work. Note that your answer will probably not be an even whole number as it is in the examples, so round to the nearest whole number.
B. Determine the Reaction Order for Na2S2O3 using calculations described in the Background section. Show your work. Note that your answer will probably not be an even whole number as it is in the examples.
Concentrations
# of drops
# of drops
# of drops
Stock Solution
Stock Solution
Reaction (after mixing in well)
Reaction (after mixing in well)
Reaction Time
(seconds)
Reaction
Rate
(sec-1)
Well #
HCl
H2O
Na2S2O3
HCl
Na2S2O3
HCl
Na2S2O3
Trial 1
Trial 2
Average
C1, D1
12
0
8
1M
0.3M
Yellow, odor
Yellow, odor
36
34
35
0.03
C2, D2
6
6
8
1M
0.3M
Yellow, odor
Yellow, odor
42
41
42.5
0.02
C3, D3
4
8
8
1M
0.3M
Yellow, odor
Yellow, odor
42
44
43
0.02
Explanation / Answer
Solution : -
Calculating order with respect to HCl
From the volume of the HCl used and the concentration of the stock solution of the HCl and volume of Na2S2O3 used we need to calculate new concentrations of the HCl in each trial after mixing the solutions.
So lets calculate the final concentration of the HCl
Trial 1
Drops of HCl = 12 drop
Drops of Na2S2O3 = 8 drop
Water drops = 0
Final concentration of HCl = initial concentration of HCl * initial volume / total volume
= 1 M * 12 frop / (8 drop +12 drop)
= 0.6 M
Trial 2
Drops of HCl = 6 drop
Drops of Na2S2O3 = 8 drop
Water drops = 6
Final concentration of HCl = initial concentration of HCl * initial volume / total volume
= 1 M * 6 drop / ( 6 drop +6 drop+8 drop )
= 0.3 M
Trial 3
Drops of HCl = 4 drop
Drops of Na2S2O3 = 8 drop
Water drops = 8
Final concentration of HCl = initial concentration of HCl * initial volume / total volume
= 1 M * 4drop / ( 4 drop + 8 drop+8 drop )
= 0.2 M
Now lets calculate the order of the HCl
Using the following set up
rate 1 / rate 2 = [HCl]1m / [HCl]2m
0.03/0.02 = (0.6/0.3)m
1.5 = 2m
Log 1.5 = m * log 2
Log 1.5 / log 2 = m
0.6 = m
Therefore order with respect to HCl is half order
Now lets calculate the order with respect to Na2S2O3
Trial 1
Drops of HCl = 8 drop
Drops of Na2S2O3 = 12 drop
Water drops = 0
Final concentration of Na2S2O3 = initial concentration of Na2S2O3 * initial volume / total volume
= 0.3 M * 12 frop / (8 drop +12 drop)
= 0.18 M
Trial 2
Drops of HCl = 8 drop
Drops of Na2S2O3 = 6 drop
Water drops = 6
Final concentration of Na2S2O3 = initial concentration of Na2S2O3 * initial volume / total volume
= 0.3 M * 6 drop / ( 6 drop +6 drop+8 drop )
= 0.09 M
Trial 3
Drops of HCl = 8 drop
Drops of Na2S2O3 =4 drop
Water drops = 8
Final concentration of Na2S2O3= initial concentration of Na2S2O3* initial volume / total volume
= 0.3 M * 4drop / ( 4 drop + 8 drop+8 drop )
= 0.06 M
Now lets calculate the order with respect to Na2S2O3 by using the following set up
( rate 1 / rate 2) = [Na2S2O3]1n / [Na2S2O3]2n
0.05/0.02 = (0.18/0.09)n
2.5 = 2n
Log 2.5 = n * log 2
Log 2.5/log 2 = n
n = 1.3
so we can round it n = 1
therefore order with respect to Na2S2O3 is first order
Therefore overall rate equation for the reaction is
Rate = K [ HCl]1/2 [Na2S2O3]
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