GROUP 4 EXPERIMENTAL SCIENCES
STUDENT LAB REPORT
IBDP Grade:
12
Name of Student:
Rachita Sompura
Session No. :
003768-002
Subject:
Chemistry
Level:
Standard
Date :
08/05/2015
Internal Assessment Criteria:
Name of Teacher:
Signature of Teacher:
Title
Salts
Title:Salts
Investigation:calculating the amount of iodine present in 5 various salts
Hypothesis:5 various salts are to be taken and the amount of iodine is to be
calculated. This will be done by the method of titration taking sodium thiosulfate in
the burette. Potassium iodide and dil. Sulfuric acid are to be mixed in the salt and
water solution. Later, after adding starch, titrate the solution and perform the
calculations by the help of the readings collected.
Variables list:
Independent variable: Types of salts (Five samples used in the expt )
Dependent variable: amount of iodine
Controlled variables: Amount of starch ,
Material list:
 Beaker (250ml)
 Burettes ( )
 Glass rods
 Graduate cylinder (50 mL) (250ml)
 Containers calibrated by volume to weigh salt
 Conical flask (250ml)
 Volumetric flasks 250 mL
 Funnel
 Weighing machine to weigh 50g of salt
Diagram or photograph
Reagents
0.005 N-Sodium Thiosulfate Solution5: Dissolve 1.24 g Na2S2O3.5H2O (FW=
248) in one liter of distilled water and store in a cool dry place. Solution is stable for 1
month. This amount is sufficient for about 200 samples.
2 N-Sulfuric Acid Solution: Using concentrated sulfuric acid, slowly add 60 mL to
900 mL of distilled water and mix. The solution is cooled down and made up to one
liter. This amount is sufficient for about 1,000 samples.
10% Potassium Iodide Solution: Dissolve 100 g of potassium iodide in water and
make up to one liter. Store in a cool dark place, this solution is stable for 6 months
provided there is no color change. This amount is sufficient for about 200 samples.
Starch Solution: Weigh 1 gram of soluble starch into a 100 mL beaker and add 10
mL of water, heat to dissolve.
The thiosulfate solution can be standardized by titrating with a standard 0.005Npotassium iodate solution. This standard solution is prepared from a 0.5 N solutions
made by dissolving 4.4585 g analytical grade KIO3 in water and making up to
250mL. The 0.5 N solution is diluted 100-fold by taking 2.5 mL and diluting to 250
mL with distilled water. Normality of the thiosulfate solution = [volume KIO3 (sol)/
volume thiosulfate (sol)]/ xm Normality of iodate solution (0.005 N)]
Prepare a saturated solution of sodium chloride dissolving NaCl in 80 mL of distilled
water, heat up the solution until no more NaCl dissolves. Cool the solution and add to
the dissolved starch, and make up to 100 mL. Store in a cool dark place, this amount
is sufficient for about 50 samples. Prepare the starch solution every day. The saturated
NaCl solution is stable for 12 months.
Procedure:
 Solubilisation of the salt sample
1. Weigh accurate 50g of salt and add the mixture of distilled water and salt
into a 250ml volumetric flask.
2. Transfer 50 ml of the salt solution Transfer 50 mL of the salt solution
using a 50 mL pipette to a 200 mL Erlenmeyer flask.
3. using a graduated pipette add 1 mL of the 2-N sulfuric acid to the salt
solution and mix thoroughly.
4. Add 5 mL of the 10% potassium iodide solution using a measuring cylinder
or a pipette. If iodine is
present a yellowish solution is formed.
5. Cover the flask and put in the dark or in a cupboard for 10 minutes.
 Titrating iodine in the salt solution
6. Fill the 50 mL burette with the thiosulfate solution in readiness for titration.
7. Titrate the iodine solution in the flask with the thiosulfate and stop the
titration when the dark color of the solution turns to pale yellow. Agitate the salt
solution continuously.
8. Add 2 mL of the starch solution and the solution should turn blue. Mix
thoroughly.
9. Resume titration with thiosulfate until the blue color disappears. Agitate the
salt solution continuously and gently.
10. Record the volume from the burette or serologic pipette as accurately as
possible to the nearest 0.1 mL.
Calculations:
The amount of potassium iodate in the salt is determined using the following
equation.
1 (mg/kg) = N Na2S2O3 (eq/L) × vol Na2S2O3 (ml) × 21.222 (g/eq l) initial volume
(ml)
w (kg) × used volume (ml)
If the procedure is strictly followed the prior formula could be simplified to:
1 (mg/kg) =0.005 Na2S2O3 (eq/L) × vol Na2S2O3 (ml) × 21.222 (g/eq l) 250 (ml)
0.05 kg × 50 (ml)
The final equation is as follows:
1 (mg/kg) = 10.61 × vol Na2S2O3 (ml)
Observations tables:
Experiment no. 1.
To calculate the iodine ppm, net reading was multiplied by 10.6 and the results were
found. For an example, the first reading:
7.6(initial reading) – 5(final reading) = 2.6(net reading)
Therefore, 2.6 × 10.61 = 27.56
The above 10.6 value is constant for all the readings taken throughout all the
experiments.
No. of
readings
1
2
3
4
5
No. of
readings
1
2
3
4
5
Salt Sample
Sample A
Salt Sample
Sample A
Initial
reading/ml
5.0
7.6
10.9
13.4
15.9
Iodine
ppm
27.6
24.4
26.5
26.5
27.6
Final
Net reading
reading/ml
ml
7.6
2.6
10.9
2.3
13.4
2.5
15.9
2.5
18.5
2.6
Average
Iodine ppm
26.52
Uncertainty
in Iodine
ppm
1.6
(Rounded
to one
decimal)
2.0
Iodine
ppm
27.6
24.4
26.5
26.5
27.6
Sample Calculation shown for averaging iodine ppm :
=
=
(27.6+24.4+26.5+26.5+27.6)
(132.6)
5
5
= 26.52
Uncertainty in Sample A:
= Maxima – Minima
2
=
27.6−24.4
2
= 1.6 Rounded to 1 dp
= 2.0
Percentage Uncertainty :
=
2.0 ∗ 100
26.52
= 7.54 %
= 8.00 %
Experiment no. 2
To calculate the iodine ppm, net reading was multiplied by 10.6 and the results below
were found. For an example, the first reading:
11.1 (initial reading) – 7.8(final reading) = 3.3(net reading)
Therefore, 3.3 × 10.6 = 35.0
The above 10.6 value is constant for all the readings taken throughout all the
experiments.
No. of
Salt
readings
1
Tata salt
2
3
4
5
Initial
reading
7.8
11.1
16.2
20.0
23.9
Final
reading
11.1
16.2
20.0
23.9
27.7
Net reading Iodine ppm
Initial
reading
26.7
29.1
31.7
34.4
37.1
Final
reading
29.1
31.7
34.4
37.1
39.9
Net reading Iodine ppm
Initial
reading
29.1
30.7
32.2
33.8
35.3
Final
reading
30.7
32.2
33.8
35.3
37.0
Net reading Iodine ppm
Initial
reading
00
Final
reading
00
Net reading Iodine ppm
3.3
4.1
3.8
3.9
3.8
35.0
43.5
40.3
41.3
40.5
Experiment no. 3
No. of
Salt
readings
1
Saffola salt
2
3
4
5
2.4
2.6
2.7
2.7
2.8
25.4
27.6
28.6
28.6
29.7
Experiment no. 4
No. of
Salt
readings
1
Topline salt
2
3
4
5
1.6
1.5
1.6
1.5
1.7
17.0
15.9
17.0
15.9
18.0
Experiment no. 5
No. of
Salt
readings
1
Salt pan
00
00
2
3
4
5
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
There was no colour change observed after adding potassium iodide and dil. sulfuric
acid or starch. Therefore, there were no readings taken and was hence proved that salt
pan does not contain iodine.
Graph :
I
o
d
i
n
e
Iodine ppm Level for 5 sample of 50 g v/s
various sample
50
45
40
35
30
25
p
20
p
m 15
10
5
0
Salt A
Salt B
Salt C
Salt sample
Salt D
Salt E
Iodine ppm v/s various salts
I
o
d
i
n
e
p
p
m
50
45
40
35
30
25
20
15
10
5
0
Series1
Salt A
Salt B
Salt C
Salt D
Salt E
Various salts
After performing the experiment we found the content of iodine is different in
various sample used in the experiment.
We also found that the last sample E was very different as compare to other salts
as the content of iodine level was almost zero throughout for five different
readings .
We calculated the average of five sample per salt and the average uncertainty for
those five different readings.
From the samples we collected for our experiment the content of iodine mention
on wrapper
Sr No.
1
2
3
4
5
Salts Sample
A
B
C
C
D
Iodine Content/mg
30.00
15.00
30.00
15.00
0.64
The percentage error in sample A was 8 %, Sample B is 10 % , Sample C is 7 %,
Sample D is 6 % and Sample E has zero iodine content which leads to NO
percentage error in that calculation.
Iodine ppm in sample A was calculated with error of 8 % so the deviation of
sample A with wrapper reading is shown below:
Deviation for A : =
Deviation for B : =
Deviation for C : =
Deviation for D : =
𝟑𝟎.𝟎𝟎−(𝟐𝟔.𝟓𝟐±𝟐.𝟎𝟎 )
𝟑𝟎.𝟎𝟎
𝟏𝟓.𝟎𝟎−(𝟒𝟎.𝟏𝟐±𝟒.𝟎𝟎 )
𝟏𝟓.𝟎𝟎
𝟑𝟎.𝟎𝟎−(𝟐𝟕.𝟗𝟖±𝟐.𝟎𝟎 )
𝟑𝟎.𝟎𝟎
𝟏𝟓.𝟎𝟎−(𝟏𝟔.𝟕𝟔±𝟏.𝟎𝟎 )
𝟏𝟓.𝟎𝟎
Deviation for E : No Deviation Found
Evaluation:
Starch :
Glassware:
Parallax Error:
Solubility Error:
= (0.049 to 0.182)
= (1.933 to 1.400)
= ( 0.00 to 0.134)
= (0.184 to 0.050)
Suggested improvements :
systemic errors: apparatus shall be cleaned with distilled water and dry. This would
reduce errors while measuring solution.
Color change of the solution shouldn’t very much.
random errors: eye level wouldn’t be accurate hence, the readings would not be very
precise.
Accurate measurements of the solutions to be taken.