EXPERIMENT 5
LAB REPORT
TITLE
Molarity and Concentration
OBJECTIVE
To determine the molarity and concentration of the dilute hydrochloric acid,
HCL by titrating it with 0.1 M sodium carbonate solution prepared in
experiment 4.
APPARATUS
i. Burette
ii. Pipette
iii. Beaker
iv. Conical Flask
v. Retort Stand
vi. White Tile
CHEMICALS
a) Dilute hydrochloric acid, HCL
b) 0.1 M sodium carbonate
c) Methyl orange indicator
THEORY
Molarity is used to express the concentration of a solution. It is also known as
molar concentration, molarity is the number of liters of solution divided by the
number of liters of solution.
The molarity of neutralization reaction can be determined by using the
formula:
2HCL + Na2 CO 3 → 2NaCl + H 2 O + C O2
General equation for the reaction between an acid A and base B:
aA + bB → cC + dD
By manipulating the equation above, we can use the formula:
MAV A a
=
MBV B b
Concentration is the abundance of a constituent divided by the total volume of
mixture. The concentration is also known as the ratio of the amount of solute
to the amount of either solvent or solution.
The formula for concentration:
Concentration (g d m−3 ) = Molarity × Molar mass
PROCEDURE
1. The burette was rinsed with distilled water and then with a little dilute
hydrochloric acid solution. Then the burette was filled with the acid
solution.
2. Some of the acid was running rapidly into an empty beaker to ensure the
capillary tube below the stopcock was filled and the air bubbles was
removed.
3. The pipette was rinsed with the distilled water and a little sodium
carbonate solution.
4. 20.0 ml portions of Na2 CO 3 solution was pipetted and poured into a
conical flask. 2 drops of methyl orange indicator was dropped into the
conical flask and the colour of the solution was recorded.
5. The conical flask was placed below the burette with the tip of the burette
just inside the flask. The white tile was placed under the conical flask.
6. The initial burette reading was recorded. Then, the acid from the burette
was slowly run into the conical flask, the flask was swirled continuously.
7. The titration was stopped as soon the color of the alkaline solution in the
flask turned orange. The final burette reading was recorded.
8. Steps (4) and (7) was repeated at least twice.
9. All the results was recorded in the titration table in the practical report
sheet.
DATA
Titration Preliminary 1 2
number
Final burette 27.40 27.60 27.50
reading, ml
Initial burette 0.00 0.00 0.00
reading, ml
Volume of HCL 27.40 27.60 27.50
used, ml
Average volume 27.55
of HCL used, ml
1. Volume of pipette used = 20.0 ml
2. The color of methyl orange indicator changed from bright orange to
pink.
3. The molarity of sodium carbonate is 0.1 M.
RESULTS
Theoretically
1) Volume of HCL needed to complete neutralization with Na 2 CO 3
,solution
1st reading = 27.60
2 reading = 27.50
nd
1 st reading +2nd reading
Average reading =
2
27.60+ 27.50
= 2
=27.55 ml
=20.0 ml Na2 CO 3 solution required 27.55 ml HCL solution for complete
neutralization.
2) Molarity of HCL:
2HCL + Na2 CO 3 → 2NaCl + H 2 O + C O2
MAV A a
=
MBV B b
M A (27.55) 2
=
(0.1)(20) 1
M A = 0.15 M
3) Concentration of HCL:
Concentration (g d m−3 ) = Molarity x molar mass
= 0.15 x 36.5
=5.48 g d m−3
Measurement
1) Accuracy
True value of volume HCL needed for complete neutralization with
Na2 CO 3 solution = 25.00 ml
Difference = 27.55 ml – 25.00 ml
= 2.55 ml
= less accurate
2) Precision
Class`s average of volume of HCL used in the neutralization reaction:
32.85+ 25.63+ 27.50+26.55+25.50
= 5
=27.61 ml
Difference = 27.61 ml – 27.55 ml
=0.06 ml
=precise
DISCUSSION
Theoretically, the molarity of hydrochloric acid, HCL in the experiment is
0.15M. The value was acquired from the neutralization reaction between 20.0
ml 0.1M sodium carbonate, Na2 CO 3 solution and 27.55 ml HCL solution.
Then, the concentration of HCL can be calculated by multiplying the molarity
with the molar mass. The concentration of HCL in the experiment is 5.48 g d
m−3 .
The accuracy of the experiment is calculated by getting the difference
between the average volume of HCL used in the neutralization reaction and the
true value of the volume of HCL needed for a complete neutralization reaction.
The difference is 2.55 ml. the difference is more than 1.0 ml which makes it less
accurate. This is happens probably due to the mistakes during conducting the
experiment such as letting the acid from the burette run to fast and did not
stop it on time when the color of the solution changed. The precision of the
experiment is tested by getting the difference of class`s average of volume of
the HCL used in the neutralization reaction and the average volume of HCL
used in the neutralization reaction. The difference is 0.06 ml. Therefore, the
experiment is less accurate but precise.
CONCLUSION
1. The molarity of dilute hydrochloric acid, HCL is 0.15 M.
2. The concentration of dilute hydrochloric acid, HCL is 5.48 g d m−3 .
