1
Unit 2 - Practical Scientific Procedures and Techniques
Learning aim A: Undertake titration and colorimetry to determine the
concentration of solutions
Contents
Introduction to calibration and the calibration check of balances ———————————- Page 2
Making a standard solution of sodium carbonate —————————————————— Page 2
Checking the calibration of the burette and pipette using water ———————————— Page 3
Standardisation of hydrochloric acid ——————————————————————-—- Page 4
Finding the unknown concentration of sodium hydroxide ———————————————Page 5
Checking the calibration of a pH probe ——————————————————————- Page 6
pH curve of the titration of HCl against NaOH ———————————————————- Page 6
Calculations: Part 1 - using sodium carbonate to standardise HCl ——————————- Page 9
Calculations: Part 2 - calculating the unknown concentration of NaOH ———————— Page 10
Evaluation of standard solution and titration practical techniques - improvements ———— Page 10
Using colorimetry to find out an unknown concentration of copper sulphate ——————- Page 11
Serial dilution method and calculations —————————————————————— Page 11
Copper sulphate absorbance table and graph ———————————————— Page 12 to 13
Evaluation of serial dilution and colorimetry techniques - improvements ———————— Page 14
Risk assessment ———————————————————————————————- Page 14
, 2
Checking the calibration of balances
Before beginning a scientific practical, it is important to check calibration as it ensures the accuracy
of the equipment used. This ensures accurate measurements of substances and therefore
improves scientific procedures.
The calibration of the balance that was used for all of my mass readings was checked using
various different known weights.
The GEC Avery balance displayed masses to 3 decimal places. As a result, I decided to use this
balance as there is less uncertainty in these readings when compared to the scalix balance (which
only displayed masses to 2 decimal places). Another reason why I chose the GEC Avery scale was
that it has a shielding that prevents air or substances within it interfering with the readings.
Mass (g) standard weight scalix (600g capacity) GEC Avery (1500g capacity)
100 99.32 99.972
50 50.98 49.983
20 19.79 19.997
10 9.85 9.996
5 4.56 4.994
2 2.11 2.001
1 0.86 0.999
To further ensure that these readings were as accurate as possible, a spirit level was used on the
counter prior to the weighing of masses to check that the surface on which the balances were
placed was not slanted (as this may effect the accuracy of the readings). Furthermore, gloves were
worn to prevent any unwanted substances transferring from the hands to the weights.
As there was not a result that was more than 0.02 g incorrect to the true masses, I was able to
conclude that the balance of choice was of very high accuracy and therefore appropriate to use in
all forthcoming scientific procedures.
Making a standard solution of sodium carbonate (Na2CO3)
With a spatula, around 1g of sodium carbonate (s) was placed into a weighing boat and onto the
calibrated balance. This mass was recorded and then carefully placed into a beaker. The empty
weighing boat was then weighed and recorded.
Mass of weighing boat and Na2CO3 (g) 50.080
Mass of empty weighing boat (g) 48.732
Mass of Na2CO3 (g) 1.348
Unit 2 - Practical Scientific Procedures and Techniques
Learning aim A: Undertake titration and colorimetry to determine the
concentration of solutions
Contents
Introduction to calibration and the calibration check of balances ———————————- Page 2
Making a standard solution of sodium carbonate —————————————————— Page 2
Checking the calibration of the burette and pipette using water ———————————— Page 3
Standardisation of hydrochloric acid ——————————————————————-—- Page 4
Finding the unknown concentration of sodium hydroxide ———————————————Page 5
Checking the calibration of a pH probe ——————————————————————- Page 6
pH curve of the titration of HCl against NaOH ———————————————————- Page 6
Calculations: Part 1 - using sodium carbonate to standardise HCl ——————————- Page 9
Calculations: Part 2 - calculating the unknown concentration of NaOH ———————— Page 10
Evaluation of standard solution and titration practical techniques - improvements ———— Page 10
Using colorimetry to find out an unknown concentration of copper sulphate ——————- Page 11
Serial dilution method and calculations —————————————————————— Page 11
Copper sulphate absorbance table and graph ———————————————— Page 12 to 13
Evaluation of serial dilution and colorimetry techniques - improvements ———————— Page 14
Risk assessment ———————————————————————————————- Page 14
, 2
Checking the calibration of balances
Before beginning a scientific practical, it is important to check calibration as it ensures the accuracy
of the equipment used. This ensures accurate measurements of substances and therefore
improves scientific procedures.
The calibration of the balance that was used for all of my mass readings was checked using
various different known weights.
The GEC Avery balance displayed masses to 3 decimal places. As a result, I decided to use this
balance as there is less uncertainty in these readings when compared to the scalix balance (which
only displayed masses to 2 decimal places). Another reason why I chose the GEC Avery scale was
that it has a shielding that prevents air or substances within it interfering with the readings.
Mass (g) standard weight scalix (600g capacity) GEC Avery (1500g capacity)
100 99.32 99.972
50 50.98 49.983
20 19.79 19.997
10 9.85 9.996
5 4.56 4.994
2 2.11 2.001
1 0.86 0.999
To further ensure that these readings were as accurate as possible, a spirit level was used on the
counter prior to the weighing of masses to check that the surface on which the balances were
placed was not slanted (as this may effect the accuracy of the readings). Furthermore, gloves were
worn to prevent any unwanted substances transferring from the hands to the weights.
As there was not a result that was more than 0.02 g incorrect to the true masses, I was able to
conclude that the balance of choice was of very high accuracy and therefore appropriate to use in
all forthcoming scientific procedures.
Making a standard solution of sodium carbonate (Na2CO3)
With a spatula, around 1g of sodium carbonate (s) was placed into a weighing boat and onto the
calibrated balance. This mass was recorded and then carefully placed into a beaker. The empty
weighing boat was then weighed and recorded.
Mass of weighing boat and Na2CO3 (g) 50.080
Mass of empty weighing boat (g) 48.732
Mass of Na2CO3 (g) 1.348
