1.1.2 - Moles and Equations

Specification

Context and exemplification - Assessable learning outcomes

The mole

Candidates should be able to:

(a) explain the terms:

(i) amount of substance,

(ii) mole (symbol mol-1), as the unit for amount of substance,

(iii) the Avogadro constant, NA, as the number of particles per mole (6.02 x 1023 mol-1);

(b) define and use the term molar mass (units g mol-1) as the mass per mole of a substance; Empirical and molecular formulae

(c) explain the terms:

(i) empirical formula as the simplest whole number ratio of atoms of each element present in a compound,

(ii) molecular formula as the actual number of atoms of each element in a molecule;

(d) calculate empirical and molecular formulae, using composition by mass and percentage compositions;

Chemical equations

(e) construct balanced chemical equations for reactions studied and for unfamiliar reactions given reactants and products; Calculation of reacting masses, mole concentrations and volumes of gases

* Candidates will be expected to calculate the above for reactants and products from chemical equations.ƒn

(f) carry out calculations, using amount of substance in mol, involving:

  • (i) mass,
  • (ii) gas volume,
  • (iii) solution volume and concentration;

(g) deduce stoichiometric relationships from calculations;

(h) use the terms concentrated and dilute as qualitative descriptions for the concentration of a solution.

The mole

Explain the terms:

Define and use the term molar mass (units g mol–1)

Mass per mole of a substance


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Empirical and Molecular Formula

Explain the terms:

Calculate empirical and molecular formulae, using composition by mass and percentage compositions;

Empirical formula = Mass/Percentage of Composition : Mass/Percentage of Composition

Molar Mass Molar Mass

Then divide by the smallest number of moles to find out the ratio.


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Chemical Equations

Construct balanced chemical equations for reactions studied and for unfamiliar reaction given reactants and products;

Things to remember:

  1. Group 7, oxygen, nitrogen and hydrogen are diatomic
  2. State symbols should usually be included in the answer, even if not asked for.
  3. Answers should always be balanced, again, even if not asked for.

Calculation of reacting masses, moles, concentrations and volumes of gases

Carry out calculations, using amount of substance in mol, involving:

(i) Pure substances

Number of moles = Mass/ molar mass

(ii) Gas volumes (at room temperature)

Number of moles = Volume(dm3)/24

(iii) Solutions

Number of moles = Concentration x Volume (dm3)

Deduce stoichiometric relationships from calculations;

Things to remember:

Use the terms concentrated and dilute as qualitative descriptions for the concentration of a solution.

Concentration: the amount of solute, in mol, per 1dm3 of solution

Concentrated: a high amount of solute per dm3 of solution

Dilute: a low amount of solute per dm3 of solution.


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