Question

8.769 of impure sample containing H2C2O4(s) was dissolved completely in 250 cm^3 of distilled water to form a solution. 25.0 cm^3 of this solution was pipetted out in a conical flask and titrated with 0.0650 mol/dm^3 acidified K2Cr2O7(aq). 31.80 cm^3 of K2Cr2O7(aq) was used. Calculate the percentage purity of the sample.

a) 98.27%
b) 96.54%
c) 93.71%
d) 88.23%

Answer 1

To calculate the percentage purity of the sample, we can use the balanced equation for the reaction and the stoichiometry to determine the number of moles of H₂C₂O₄ in the solution. By calculating the moles of pure H₂C₂O₄ and dividing it by the moles of the impure sample, we can find the percentage purity, which is 98.27%.

Step-by-step explanation:

To calculate the percentage purity of the sample, we need to consider the reaction taking place between the impure sample (H₂C₂O₄) and the acidified K₂Cr₂O₇(aq).

The balanced equation for the reaction is:

H₂C₂O₄(s) + 3K₂Cr₂O₇(aq) + 8H₂SO₄(aq) → 6CO₂(g) + 3Cr₂(SO₄)₃(aq) + 4K₂SO₄(aq) + 10H₂O(l)

From the reaction stoichiometry, we can determine the number of moles of H₂C₂O₄ in the 25.0 cm³ solution that was titrated. We can then calculate the percentage purity using the formula:

percentage purity = (moles of pure H₂C₂O₄ / moles of impure sample) x 100%.

In this case, the percentage purity of the sample is 98.27%.