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Edexcel IGCSE Chemistry 1.28 Amount of substance calculations

Practise calculations linking amount of substance, Mr, Ar, particle numbers and percentage by mass from formulae, graphs and reaction data.

Syllabus
First assessment 2019
Course
Chemistry 4CH1

Exam points

  • calculate moles from mass and Mr, then convert to particles using Avogadro data
  • determine percentage by mass from formulae and given Mr values
  • read graph or results data to find amount of substance before further calculation

1.28 Amount of substance calculations question 1

[Maximum number: 3]

The diagram shows the positions of some elements in part of the Periodic Table.

Na Al S Cl
K Xe
In

Table for Question 1.28 Amount of substance calculations question 1 — Edexcel IGCSE Chemistry

A teacher adds a small piece of sodium to a glass trough containing water and universal indicator.

The universal indicator changes colour.
The equation for the reaction is

2Na( s)+2H2O(l)→2NaOH(aq)+H2( g)2 \mathrm{Na}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})

The reaction with sodium produces 0.036 g of hydrogen gas.

One mole of hydrogen gas contains 6.0×10236.0 \times 10^{23} molecules.
Calculate the number of molecules of hydrogen gas produced in the reaction with sodium.

Give your answer to two significant figures.
number of molecules of hydrogen gas =

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