Mc questions - a level chem

Stuck on these questions, help appreciated
Q15.
The apparatus in the figure below was set up to measure the time taken for 20.0
cm3 of sodium thiosulfate solution to react with 5.0 cm3 of hydrochloric acid in a
100 cm3 conical flask at 20 °C. The timer was started when the sodium
thiosulfate solution was added to the acid in the flask. The timer was stopped
when it was no longer possible to see the cross on the paper.
AQA Chemistry A-Level - Kinetics QP PhysicsAndMathsTutor.com
Page 19 of 22
What is likely to decrease the accuracy of the experiment?
A Rinsing the flask with acid before each new experiment.
B Stirring the solution throughout each experiment.
C Using the same piece of paper for each experiment.
D Using different measuring cylinders to measure the volumes
of acid and sodium thiosulfate.
ANSWER: A (Don't get this, I thought acid rinsing might make it more reliable? than potentially diluting the acid by rinsing with water)
Q16.
The experiment was repeated at 20 °C using a 250 cm3 conical flask.
Which statement is correct about the time taken for the cross to disappear when
using the larger conical flask?
A The time taken will not be affected by using the larger conical flask.
B The time taken will be decreased by using the larger conical flask.
C The time taken will be increased by using the larger conical flask.
D It is impossible to predict how the time taken will be affected by
using the larger conical flask.
ANSWER = C

Stuck on these questions, help appreciated
Q15.
The apparatus in the figure below was set up to measure the time taken for 20.0
cm3 of sodium thiosulfate solution to react with 5.0 cm3 of hydrochloric acid in a
100 cm3 conical flask at 20 °C. The timer was started when the sodium
thiosulfate solution was added to the acid in the flask. The timer was stopped
when it was no longer possible to see the cross on the paper.
AQA Chemistry A-Level - Kinetics QP PhysicsAndMathsTutor.com
Page 19 of 22
What is likely to decrease the accuracy of the experiment?
A Rinsing the flask with acid before each new experiment.
B Stirring the solution throughout each experiment.
C Using the same piece of paper for each experiment.
D Using different measuring cylinders to measure the volumes
of acid and sodium thiosulfate.
ANSWER: A (Don't get this, I thought acid rinsing might make it more reliable? than potentially diluting the acid by rinsing with water)
Q16.
The experiment was repeated at 20 °C using a 250 cm3 conical flask.
Which statement is correct about the time taken for the cross to disappear when
using the larger conical flask?
A The time taken will not be affected by using the larger conical flask.
B The time taken will be decreased by using the larger conical flask.
C The time taken will be increased by using the larger conical flask.
D It is impossible to predict how the time taken will be affected by
using the larger conical flask.
ANSWER = C