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Edexcel A-Level Chemistry AS 8.20 Solution Concentrations in Mol Dm 3 And G Dm 3 Questions

Practise Edexcel IAL Chemistry 8.20 by using titre data, mole ratios and molar mass, then choosing indicators and reporting exact endpoint colours.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
AS

Exam points

  • Calculate concentration from a mean titre, pipetted volume and reaction mole ratio.
  • Convert between mol dm⁻³ and g dm⁻³ using molar mass and suitable significant figures.
  • Choose methyl orange or phenolphthalein and state its exact endpoint colour change.

Edexcel A-Level Chemistry AS 8.20 Solution Concentrations in Mol Dm 3 And G Dm 3 Questions question 1

[Maximum number: 6]

A student carried out an experiment to identify the metal M in the hydrated carbonate M2CO3⋅10H2O\mathrm{M}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}. A solution was made by dissolving 3.56 g of the hydrated metal carbonate in distilled water and making the volume up to 250.0 cm3250.0 \mathrm{~cm}^{3} in a volumetric flask. 25.0 cm325.0 \mathrm{~cm}^{3} of this solution was placed in a conical flask and titrated with 0.100 moldm−30.100 \mathrm{~mol} \mathrm{dm}^{-3} of hydrochloric acid. The equation for the reaction is

M2CO3(aq)+2HCl(aq)→2MCl(aq)+H2O(l)+CO2( g)\mathrm{M}_{2} \mathrm{CO}_{3}(\mathrm{aq})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow 2 \mathrm{MCl}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{CO}_{2}(\mathrm{~g})

Question (a)

(a)

Methyl orange indicator was used in this titration. Give the colour change in the conical flask at the end-point. Colour change from to

[ 2 ]

Question (b)

(b)

The results of the titration are shown.

Table for Question (b) — Edexcel A-Level Chemistry AS
[ 4 ]

Question (i)

(i)

Using your answer to (c)(ii), calculate the number of moles of HCl in the mean titre.

[ 1 ]

Question (ii)

(ii)

Calculate the number of moles of M2CO3\mathrm{M}_{2} \mathrm{CO}_{3} in 25.0 cm325.0 \mathrm{~cm}^{3} of the solution. Hence calculate the number of moles of M2CO3\mathrm{M}_{2} \mathrm{CO}_{3} in the 250.0 cm3250.0 \mathrm{~cm}^{3} volumetric flask.

[ 2 ]

Question (iii)

(iii)

Using your answer in (c)(iv) and the mass of M2CO3⋅10H2O\mathrm{M}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O} in the 250 cm3250 \mathrm{~cm}^{3} of solution, calculate the molar mass of M2CO3⋅10H2O\mathrm{M}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}.

[ 1 ]
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