05. 3.0g of impure Na:C0, is dissolved in water and the solution is made up to 250ml. To 50ml
of this solution, 50ml of 0.1N HCI is added to the mixture, for complete neutralization.
Calculate the percentage purity of the sample of Na:CO3.
Answers
Answer:
You're titrating hydrochloric acid,
HCl
, a strong acid, with sodium hydroxide,
NaOH
, a strong base, so right from the start you should know that the pH at equivalence point must be equal to
7
.
Hydrochloric acid and sodium hydroxide react in a
1
:
1
mole ratio to form water and aqueous sodium chloride
HCl
(aq]
+
NOH
(aq]
→
NaCl
(aq]
+
H
2
O
(l]
The net ionic equation for this reaction looks like this
H
3
O
+
(aq]
+
OH
−
(aq]
→
2
H
2
O
(l]
Now, the equivalence point corresponds to a complete neutralization, i.e. when you add enough strong base to completely consume all the acid present in the solution.
The
1
:
1
mole ratio tells you that at the equivalence point, the solution must contain equal numbers of moles of strong acid and strong base.
Your tool of choice here will the equation
∣
∣
∣
∣
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
a
a
pH
=
−
log
(
[
H
3
O
+
]
)
a
a
∣
∣
−−−−−−−−−−−−−−−−−−−−−−−−
Now, it's very important to realize that the volume of the solution will increase as you add the strong base solution. Keep this in mind when calculating the