Amount of substance exam questions

Question 1

The student rinses the burette with deionised water before filling with
sodium hydroxide solution.
State and explain the effect, if any, that this rinsing will have on the value of
the titre.

Answer 1

M1=Titre value would increase larger value
M2 = Because the sodium hydroxide solution would be more dilute

Question 2

The student noticed that some of the liquid injected into the gas syringe did
not vaporise.
Explain the effect that this has on the Mr calculated by the student

Answer 2

Calculated Mr value would be greater than actual as
A lower volume would have been recorded

Question 3

Importance of percentage yield

Answer 3

idea of getting as much product as possible in the reaction

Question 4

State why the student should use sodium hydroxide solution rather than
water for the final rinse of the burette.

Answer 4

use of water would dilute the NaOH

Question 5

Importance of percentage atom economy

Answer 5

idea of maximising the mass of reactants

Question 6

Suggest two reasons why the sulfur dioxide by-product of this process is
removed from the exhaust gases.

Answer 6

Prevents acid rain
Toxic OR causes breathing problems

Question 7

The student used a wash bottle containing deionised water when
approaching the end-point to rinse the inside of the conical flask.
Explain why this improved the accuracy of the titration.

Answer 7

Idea that it ensures all sodium hydroxide as some of the reactant would be on the side

Question 8

Give the meaning of the term concordant titres.

Answer 8

Titres that are within 0.1 cm3 of each other