PRACTICAL AA

Question 1

Explain and improve on this source of error:
Colour change is visually observed

Answer 1

It is difficult to determine exact colour due to subjectivity, making the results inaccurate
;
Use a colorimeter to detect change in colour of reaction mixture

Question 2

Explain and improve on this source of error:
Measuring cylinders (or something imprecise) were used to measure small volumes of liquids

Answer 2

The instrument is imprecise, so the volume measured is imprecise
;
Use 1cm3 / 10cm3 syringes instead

Question 3

Explain and improve on this source of error:
(reagent/solution) was not added at same time

Answer 3

Duration of reaction in test tubes were inconsistent
;
Carry out experiment one at a time, standardising the duration for every test tube

Question 4

Explain and improve on this source of error:
Temperature of water bath was not constant

Answer 4

Reaction is not taking place at designated temperature
;
Use a thermostatically controlled water bath instead set at the desired temperature

Question 5

Explain and improve on this source of error:
Lack of repeats of experiment for each sample

Answer 5

Compromises reliability of results
;
Have 3 repeats of experiment / replicates for each sample and find the mean

Question 6

Explain and improve on this source of error:
Reusing of ___

Answer 6

Leads to cross-contamination / change in concentration
;
Use one _ for each ….

Question 7

Explain and improve on this source of error:
Bubbles can be different in size / too fast to be counted

Answer 7

Inaccurate way of counting
;
Channel gas into gas syringe and calculate the volume of gas / Dilute reagent used