Oxford Cambridge and RSA
Friday 20 June 2025 – Morning
A Level Chemistry B (Salters)
H433/03 Practical skills in chemistry
Practical Insert
Time allowed: 1 hour 30 minutes
* 1 9 4 3 4 5 7 0 8 5 *
INSTRUCTIONS
• Do not send this Insert for marking. Keep it in the centre or recycle it.
INFORMATION
• This document has 4 pages.
© OCR 2025 [601/5371/4] OCR is an exempt Charity
DC (PQ/CT) 344776/3 Turn over
for more: tyrionpapers.com
, 2
Determining the percentage by mass of manganese in a steel paperclip
Most steels contain some manganese to increase the hardness of the alloy.
A group of students use colorimetric analysis to determine the percentage by mass of manganese in a
steel paperclip.
Background
The students first convert the manganese in the paperclip into a solution containing the purple
manganate(VII) ion, MnO4–(aq).
The students then use colorimetry to determine the concentration of MnO4–(aq) in the solution.
Method – Part 1 (dissolving the paperclip)
• The students cut up a paperclip and weigh out about 0.2 g.
• They dissolve this in 70 cm3 of hot dilute nitric acid in a beaker.
The nitric acid oxidises the manganese to Mn2+(aq) ions.
• They then add about 10 cm3 of KIO4(aq) to the beaker which oxidises the Mn2+(aq) to purple
MnO4–(aq) ions.
• They then make the solution accurately up to 100.0 cm3.
Method – Part 2 (preparing a calibration graph to determine the concentration of the MnO4–(aq)
solution from the paperclip)
• The students set up a colorimeter with a green filter and zero the colorimeter using deionised
water.
• The students have a set of standard solutions of MnO4–(aq) in sulfuric acid.
• They measure the absorbance of these standard solutions.
• They plot a calibration graph.
• They measure the absorbance of their MnO4–(aq) from Part 1.
• They use their result to calculate the concentration of MnO4–(aq) in the solution.
• They use this result to calculate the percentage of manganese in the paperclip.
Results
Mass of paperclip dissolved = 0.198 g
Absorbance value of paperclip solution = 0.18
© OCR 2025 H433/03 Jun25
for more: tyrionpapers.com
, 3
Calibration graph
0.40
0.35
0.30
0.25
Absorbance 0.20
0.15
0.10
0.05
0
0 5 10 15 20 25 30
Concentration of MnO4– (aq) / 10–5 mol dm–3
END OF INSERT
© OCR 2025 H433/03 Jun25
for more: tyrionpapers.com
Friday 20 June 2025 – Morning
A Level Chemistry B (Salters)
H433/03 Practical skills in chemistry
Practical Insert
Time allowed: 1 hour 30 minutes
* 1 9 4 3 4 5 7 0 8 5 *
INSTRUCTIONS
• Do not send this Insert for marking. Keep it in the centre or recycle it.
INFORMATION
• This document has 4 pages.
© OCR 2025 [601/5371/4] OCR is an exempt Charity
DC (PQ/CT) 344776/3 Turn over
for more: tyrionpapers.com
, 2
Determining the percentage by mass of manganese in a steel paperclip
Most steels contain some manganese to increase the hardness of the alloy.
A group of students use colorimetric analysis to determine the percentage by mass of manganese in a
steel paperclip.
Background
The students first convert the manganese in the paperclip into a solution containing the purple
manganate(VII) ion, MnO4–(aq).
The students then use colorimetry to determine the concentration of MnO4–(aq) in the solution.
Method – Part 1 (dissolving the paperclip)
• The students cut up a paperclip and weigh out about 0.2 g.
• They dissolve this in 70 cm3 of hot dilute nitric acid in a beaker.
The nitric acid oxidises the manganese to Mn2+(aq) ions.
• They then add about 10 cm3 of KIO4(aq) to the beaker which oxidises the Mn2+(aq) to purple
MnO4–(aq) ions.
• They then make the solution accurately up to 100.0 cm3.
Method – Part 2 (preparing a calibration graph to determine the concentration of the MnO4–(aq)
solution from the paperclip)
• The students set up a colorimeter with a green filter and zero the colorimeter using deionised
water.
• The students have a set of standard solutions of MnO4–(aq) in sulfuric acid.
• They measure the absorbance of these standard solutions.
• They plot a calibration graph.
• They measure the absorbance of their MnO4–(aq) from Part 1.
• They use their result to calculate the concentration of MnO4–(aq) in the solution.
• They use this result to calculate the percentage of manganese in the paperclip.
Results
Mass of paperclip dissolved = 0.198 g
Absorbance value of paperclip solution = 0.18
© OCR 2025 H433/03 Jun25
for more: tyrionpapers.com
, 3
Calibration graph
0.40
0.35
0.30
0.25
Absorbance 0.20
0.15
0.10
0.05
0
0 5 10 15 20 25 30
Concentration of MnO4– (aq) / 10–5 mol dm–3
END OF INSERT
© OCR 2025 H433/03 Jun25
for more: tyrionpapers.com
