The percentage by mass of iron in a steel wire is determined by a student. The student - reacts 680 mg of the wire with an excess of sulfuric acid, so that all of the iron in the wire forms Fe²⁺(aq) - makes up the volume of the Fe²⁺(aq) solution to exactly 100 cm³ - takes 25.0 cm³ portions of the Fe²⁺(aq) solution - titrates each portion with 0.0200 mol dm⁻³ potassium manganate(VII) solution. 1. Give the equation for the reaction between iron and sulfuric acid. 2. The titration results are shown in Table 3. Table 3 | Final volume / cm³ | 22.90 | 45.60 | 22.60 | | Initial volume / cm³ | 22.90 | 22.70 | 22.60 | | Titre / cm³ | 22.90 | 22.70 | 22.60 | Calculate the mean titre. 3. Give the overall ionic equation for the oxidation of Fe²⁺ by manganate(VII) ions, in acidic conditions. 4. State the colour change seen at the end point of the titration. 5. Name the piece of apparatus used for these stages of the method. Taking the 25.0 cm³ portions ________________. Adding the potassium manganate(VII) solution ________________. 6. The balance used to weigh the 680 mg of iron wire has an uncertainty of ±0.005 g. A container was weighed and its mass was subtracted from the total mass of the container and wire. Calculate the percentage uncertainty in using the balance.

A-Level AQA Chemistry Oxidation, Reduction & Redox Equations: The percentage by mass of iron i

The percentage by mass of iron in a steel wire is determined by a student - AQA - A-Level Chemistry - Question 5 - 2019 - Paper 3

Question 5

The percentage by mass of iron in a steel wire is determined by a student. The student - reacts 680 mg of the wire with an excess of sulfuric acid, so that all of ... show full transcript

Worked Solution & Example Answer:The percentage by mass of iron in a steel wire is determined by a student - AQA - A-Level Chemistry - Question 5 - 2019 - Paper 3

Step 1

Give the equation for the reaction between iron and sulfuric acid.

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Answer

The equation for the reaction between iron and sulfuric acid is:

ext{Fe} + ext{H}_2 ext{SO}_4 ightarrow ext{FeSO}_4 + ext{H}_2

Step 2

Calculate the mean titre.

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Answer

To calculate the mean titre, we add the titres and divide by the number of titrations:

Mean titre = (rac{22.90 + 22.70 + 22.60}{3} = 22.73 , \text{cm}^3)

Step 3

Give the overall ionic equation for the oxidation of Fe²⁺ by manganate(VII) ions in acidic conditions.

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Answer

The overall ionic equation is:

ext{MnO}_4^- + 5 ext{Fe}^{2+} + 8 ext{H}^+ \rightarrow ext{Mn}^{2+} + 5 ext{Fe}^{3+} + 4 ext{H}_2 ext{O}

Step 4

State the colour change seen at the end point of the titration.

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Answer

The colour change seen at the end point of the titration is from colourless to pale pink.

Step 5

Name the piece of apparatus used for these stages of the method.

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Answer

For taking the 25.0 cm³ portions, a pipette is used.

For adding the potassium manganate(VII) solution, a burette is used.

Step 6

Calculate the percentage uncertainty in using the balance.

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Answer

The percentage uncertainty can be calculated using the formula:

ext{Percentage Uncertainty} = \left( \frac{ ext{Uncertainty}}{ ext{Measurement}} \right) \times 100 over the uncertainty in the mass of wire (0.005 g) and measured mass (0.680 g): \ \text{Percentage Uncertainty} = \left( \frac{0.005}{0.680} \right) \times 100 = 0.735\, \text{or} \approx 0.74\%.

The percentage by mass of iron in a steel wire is determined by a student - AQA - A-Level Chemistry - Question 5 - 2019 - Paper 3

Worked Solution & Example Answer:The percentage by mass of iron in a steel wire is determined by a student - AQA - A-Level Chemistry - Question 5 - 2019 - Paper 3

Give the equation for the reaction between iron and sulfuric acid.

Calculate the mean titre.

Give the overall ionic equation for the oxidation of Fe²⁺ by manganate(VII) ions in acidic conditions.

State the colour change seen at the end point of the titration.

Name the piece of apparatus used for these stages of the method.

Calculate the percentage uncertainty in using the balance.

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