Chemistry Lab
Name: Emily Shah
Class: L6A
Date: January 29, 2024
Lab#: 10
Title: Redox Titration of iron (ii) salt
Aim: To investigate the unknown iron (ii) salt via a redox presentation
Teacher: Ms Naughton
Materials/ Apparatus:
-
250mL volumetric flask
-
Funnel (2)
-
50cm3 burette
-
250mL beaker
-
Conical flasks (4)
-
Stirring rod
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Spatula
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Iron (ii) salt
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0.02moldm-3 acidified potassium permanganate solution
-
Dilute sulphuric acid
Method:
1. 3.75g of iron (ii) salt and 25mL of dilute H2SO4 was measured and added to a beaker
until the salt dissolved
2. This solution was transferred to a 250mL volumetric flask and filled to the mark with
distilled water, after which it was inverted twice to evenly distribute and mix
3. 25mL of this solution was added to a conical flask
4. This solution was titrated against the acidified potassium permanganate solution until a
permanent light pink hue remained
5. Steps 3 and 4 were repeated for more accurate results
Results:
TABLE SHOWING THE VOLUME OF POTASSIUM PERMANGANATE (KMnO4)
NEEDED TO NEUTRALIZE THE SOLUTION OF DILUTE SULPHURIC ACID (H2SO4)
AND IRON (II) SALT
Rough
Trial 1
Trial 2
Trial 2
Trial 3
0.00
0.00
0.00
0.00
0.00
22.80
22.20
23.10
22.10
22.20
Volume used 22.80
22.20
23.10
22.10
22.20
Initial
Volume
(/mL)
Final
Volume
(/mL)
(/mL)
Data Analysis:
Average volume of KMnO4 used = (22.20 + 22.10 + 22.20) / 3
= 22.16mL of KMnO4
Number of moles of KMnO4 used = 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛(𝑚𝑜𝑙𝐿−1 ) × 𝑣𝑜𝑙𝑢𝑚𝑒 (𝐿)
0.02𝑚𝑜𝑙𝐿−1 × 0.02216𝑑𝑚3
= 0.0004432𝑚𝑜𝑙 𝑜𝑓 𝐾𝑀𝑛𝑂4
Balanced Ionic Equation
𝐹𝑒𝑆𝑂4(𝑎𝑞) + 𝐻2 𝑆𝑂4(𝑎𝑞) → 𝐹𝑒(𝑆𝑂4 )3(𝑎𝑞) + 𝐻2 𝑂(𝑙)
2−
2−
𝐹𝑒 2+ (𝑎𝑞) + 𝑆𝑂4(𝑎𝑞)
+ 2𝐻 + (𝑎𝑞) + 𝑆𝑂4(𝑎𝑞)
→ 𝐹𝑒2 (𝑆𝑂4 )3(𝑎𝑞) + 2𝐻2 𝑂(𝑙)
𝐹𝑒 2+ (𝑎𝑞) + 2𝐻 + (𝑎𝑞) → 𝐹𝑒2 (𝑆𝑂4 )3(𝑎𝑞) + 2𝐻2 𝑂(𝑙)
𝑀𝑛𝑂4− + 5𝑒 − + 8𝐻 + → 𝑀𝑛2+ + 4𝐻2 𝑂
Combined:
𝟐+
𝟓𝑭𝒆𝟐+ (𝒂𝒒) + 𝟏𝟎𝑯+ (𝒂𝒒) + 𝑴𝒏𝑶−
𝟒(𝒂𝒒) → 𝟓𝑭𝒆𝟐 (𝑺𝑶𝟒 )𝟑(𝒂𝒒) + 𝟏𝟎𝑯𝟐 𝑶(𝒍) + 𝑴𝒏(𝒂𝒒)
Mole ratio of Mn𝑂4− to Fe2+ = 1 : 5
Therefore, the number of moles of in 25cm3 of Fe2+ is 0.0004432𝑚𝑜𝑙 × 5
0.002216𝑚𝑜𝑙 𝑜𝑓 𝐹𝑒 2+
The number of moles of in 250cm3 of Fe2+ is
0.02216𝑚𝑜𝑙 𝑜𝑓 𝐹𝑒 2+
So, the relative formula mass of the iron (ii) salt is:
𝑀𝑎𝑠𝑠 (𝑔)
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠
3.75𝑔
0.02216𝑚𝑜𝑙
𝟏𝟔𝟗. 𝟐𝒈𝒎𝒐𝒍−𝟏
Therefore, it can be inferred that the salt used was ferrous sulphate (FeSO4).
Sources of error:
-
Overshooting the end point of the titration can cause inaccurate results
-
Inaccuracies in weighing the mass of the salt can lead to errors in the results
Precaution:
-
Caution must be practiced when handling the volumetric flask containing the H2SO4 and
iron(ii) salt. This reaction is exothermic, and thus the volumetric flask was very hot.
Conclusion:
The salt used was found to be ferrous sulphate FeSO4 via a redox titration
References:
-
Admin. (2022, December 20). Ferrous sulfate (FESO4) - Structure, formula, properties,
uses, and FAQs of ferrous sulfate. BYJUS. https://byjus.com/chemistry/ferrous-sulfate/
-
Testbook. (2023, May 15). Ferrous sulfate: Symbol, formula, structure, Properties, uses.
Testbook. https://testbook.com/chemistry/ferrous-sulfate
-
Concentration and Moles (AQA) — the science sauce. (n.d.). The Science Sauce.
https://www.thesciencehive.co.uk/concentration-and-moles-aqa
-
Molarity. (n.d.). [Video]. https://www.khanacademy.org/science/ap-chemistrybeta/x2eef969c74e0d802:intermolecular-forces-andproperties/x2eef969c74e0d802:solutions-and-mixtures/v/molarity