sources of errors

Question 1

*impurities present in glassware react with B

Answer 1

LARGER volume of B is required

Question 2

*impurities present in glassware react with P

Answer 2

SMALLER volume of B is required

Question 3

burette was not rinsed with B and only rinsed rinsed w water

Answer 3

LARGER volume of B is required
–> B is diluted (lower concentration)

Question 4

pipette was not rinsed with P and only rinsed with water

Answer 4

SMALLER volume of B is required
–> P is diluted (lower concentration)
–> since volume of P transferred into conical flask remains at 25.0cm^3, no. of moles of P transferred is less

Question 5

burette was rinsed w P instead of B

Answer 5

LARGER volume of B is required
–> P used to rinse burette will react with B that was used to fill the burette
–> B is diluted

Question 6

pipette was rinsed with B instead of P

Answer 6

SMALLER volume of B is required
–> B used to rinse pipette will react with P that was used to fill the pipette
–> P is diluted
–> since volume of P transferred into conical flask remains at 25.0cm^3, no. of moles of P transferred is less

Question 7

conical flask rinsed w P

Answer 7

LARGER volume of B is required
–> more P is present in the conical flask
–> more B is needed to react with the additional P

Question 8

conical flask was rinsed with B

Answer 8

SMALLER volume of B is required
–> less B from burette is required to react with P

Question 9

parallax error
- reading burette from above eye level when reading initial reading of burette; or
- reading burette from below eye level when reading final reading of burette

Answer 9

LARGER volume of B is calculated
–> initial reading of B will decrease (initial reading of B was recorded lower in magnitude as compared to actual reading) / final reading or B will increase (final reading of B was recorded higher in magnitude as compared to actual reading)
–> (final reading - initial reading) will increase

Question 10

parallax error
- reading burette from below eye level when reading initial reading of burette; or
- reading burette from above eye level when reading final reading of burette

Answer 10

SMALLER volume of B is calculated
–> initial reading of B will increase (initial reading of B was recorded higher in magnitude as compared to actual reading) / final reading of B will decrease (final reading of B was recorded lower in magnitude as compared to the actual reading)
–> (final reading - initial reading) will decrease

Question 11

there was a bubble in the burette that was not removed (assuming it was removed during titration)

Answer 11

LARGER volume of B is calculated
–> final reading recorded will be larger than the actual reading

Question 12

filter funnel in the burette that was not removed (assuming residual drops of B flowed into burette during titration)

Answer 12

SMALLER volume of B is calculated
–> final reading recorded will be smaller than actual reading
–> (final reading - initial reading) will decrease

Question 13

volume larger than 25.0cm^3 was used to fill the pipette (possible cause: filling above mark due to parallax error)

Answer 13

LARGER volume of B is required
–> larger volume of P is transferred to conical flask

Question 14

volume smaller than 25.0cm^3 was used to fill pipette

possible causes: filling below the mark due to parallax error, reading the tip of the meniscus, failed to remove bubble in pipette

Answer 14

SMALLER volume of B is required
–> smaller volume of P is transferred to conical flask

Question 15

did not add drop-wise when nearing end-point

Answer 15

LARGER volume of B is used

Question 16

did not swirl the contents in the conical flask

Answer 16

LARGER volume of B is used

Question 17

did not rinse the inner walls of the conical flask with distilled water during titration

Answer 17

LARGER volume of B is used
–> may cause some B to remain unreacted on the inner walls of the conical flask

Question 18

did not interpret the colour of end-point correctly (i.e. colour of solution with excess of B regarded as colour of end-point)

Answer 18

LARGER volume of B is used

Question 19

larger/smaller volume of B is required…

Answer 19

to react with P and neutralise it

Question 20

redox

Answer 20

inaccurate determination of concentration of reducing/oxidising agent as xx is higher/lower than the actual concentration