water displaced (mL) Time (seconds) 2 174 4 218 6 273 8 317 10 376 12 421 14 456
ID: 549079 • Letter: W
Question
water displaced (mL)
Time (seconds)
2
174
4
218
6
273
8
317
10
376
12
421
14
456
16
502
18
584
20
614
22
679
water displaced (mL)
Time (seconds)
2
201
4
246
6
292
8
331
10
397
12
436
14
489
16
541
18
584
20
631
22
702
water displaced (mL)
Time (seconds)
2
194
4
229
6
285
8
328
10
382
12
413
14
469
16
512
18
590
20
622
22
691
(a) Assuming the undiluted catalyst solution is 1% mass/volume I3K, how many moles of I3K are present in reactions 1 and 3? The molecular weight of I3K is 420 g/mol.
(b) What is [I3K] present in reactions 1 and 3 in units of molarity?
(c) What is [I3K] present in reaction 2 in units of molarity?
Chart 1: 10 mL undiluted 1-2% IKI; and 5 ml 3% H2O2
Chart 2: 10 mL 0.5-1.0% IKI; and 5 ml 3% H2O2
Chart 3: 10 mL undiluted 1-2% IKI; and 5 ml 2.25% H2O2
water displaced (mL)
Time (seconds)
2
174
4
218
6
273
8
317
10
376
12
421
14
456
16
502
18
584
20
614
22
679
Explanation / Answer
(a) Given, the undiluted catalyst solution is 1% mass/volume I3K
As we know the 1% mass/volume means that 1g of solute in 100 ml of solution.
Volume of undiluted solution = 10 mL
100 ml solution contains I3K catalyst = 1 g
10 ml solution contains I3K catalyst = 1x10/100 = 0.1 g
molecular weight of I3K = 420 g/mol
No. of moles of I3K = weight or mass of I3K/molecular weight of I3K = 0.1g /420 g/mol = 2.381x10-4
Hence, No. of moles of I3K present in the reaction 1 and 3 are 2.381x10-4.
(b) Molarity of the I3K = no. of moles of I3K/volume of solution (L)
We know the no. of moles of the I3K (2.381x10-4 moles) and volume of solution (10 mL + 5 mL = 15 mL).
Hence,
concentration of I3K = [I3K] = (2.381x10-4 / 15 ml)x1000
= 1.587x10-2 M
Hence [I3K] present in reaction 1 and 3 is 2.381x10-2 M
(c) In case of reaction 2, the percentage of I3K become half ( 0.5% mass/volume).
Hence concentration of I3K, in this case, becomes half of the reaction 1 and 3.
[I3K] = 1.587x10-2 M/2 = 7.94x10-3 M
Hence [I3K] present in reaction 2 is 7.94x10-3 M
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