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

Select concordant titres and calculate their mean, convert volumes to dm³, follow the balanced-equation ratio and report concentration with justified precision.

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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