Calculate the mass of sodium hydroxide, relative formula mass 40, needed to make 250 cm³ of solution of concentration 2.00 mol/dm³.

2.00 × 0.250 = 0.500 mol, and 0.500 × 40 = 20.0 g, given to 3 significant figures.

Calculate the mass of potassium hydroxide, relative formula mass 56, in 50.0 cm³ of solution of concentration 0.100 mol/dm³.

0.100 × 0.0500 = 0.00500 mol, and 0.00500 × 56 = 0.280 g, given to 3 significant figures.

What volume of a solution of concentration 0.500 mol/dm³ contains 0.100 mol of solute?

0.100 ÷ 0.500 = 0.200 dm³, which is 200 cm³, given to 3 significant figures.

OCR GCSE Combined Science Chemistry J250

Chemical Reactions

Topic overview Writing formulae of elements and compounds Balanced equations, and deducing formulae from ions Ionic equations, and state symbols The mole and the Avogadro constant Conservation of mass, and changes of mass in open systems Stoichiometry, and calculating reacting masses Exothermic and endothermic reactions, and reaction profiles Activation energy, and bond energy calculations Oxidation and reduction, by oxygen and by electrons Acids, alkalis and neutralisation The ionic equation for neutralisation, and reactions of acids Dilute and concentrated, weak and strong The pH scale, and hydrogen ion concentration pH as a factor of ten, and measuring pH Products at the electrodes, and molten ionic compounds Electrolysis of aqueous solutions Inert and non-inert electrodes

Elements, Compounds and Mixtures

Topic overview Purity, and melting point data Relative formula mass and empirical formulae Formulations, and separating mixtures Paper and thin layer chromatography Interpreting chromatograms and Rf values Choosing a purification method Metals and non-metals in the Periodic Table Electron arrangement and position in the Periodic Table Ionic, covalent and metallic bonding compared Dot and cross diagrams, and the limits of models Reactions, electron arrangement and Mendeleev's table Carbon's four bonds, and the variety of organic compounds Diamond, graphite, fullerenes and graphene Bond strength, intermolecular forces and predicting state Bulk properties of ionic, molecular and giant structures

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Biological methods of metal extraction Life cycle assessment Recycling, and the decisions behind it Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking The Earth's early atmosphere, and how oxygen developed The greenhouse effect, and evidence for climate change Effects of carbon dioxide and methane, and air pollutants Producing potable water

Monitoring and Controlling Chemical Reactions

Topic overview Mass of solute, concentration and dilution calculations Measuring the rate of a reaction, and rate graphs Factors affecting rate, and collision theory Surface area and rate Catalysts and how they work Reversible reactions and dynamic equilibrium Changing the conditions of an equilibrium Activation energy, and enzymes as catalysts

Particles

Topic overview The particle model and changes of state Limitations of the particle model How the atomic model changed, and the structure of the atom The size of atoms, and the subatomic particles Calculating protons, neutrons and electrons

Predicting and Identifying Reactions

Topic overview Groups 1, 7 and 0, and why they behave as they do Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine

Monitoring and Controlling Chemical Reactions

Mass of solute, concentration and dilution calculations

3 things to know
Paper 10 (Chemistry)

Overview

How the mass of solute and the volume of solution decide the concentration, the effect of adding water, concentration in g/dm³, and calculating masses, volumes and concentrations in mol/dm³ for sodium and potassium hydroxide solutions, including a dilution.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How does the mass of solute dissolved affect the concentration of a solution when the volume is fixed?

Key term

Water is added to a solution without adding any more solute. Explain what happens to the concentration.

Key term

State the relationship between the mass of solute, the volume of solution and the concentration in g/dm³.

Questions from this subtopic

Each one with the model answer underneath.

1
How does the mass of solute dissolved affect the concentration of a solution when the volume is fixed?
Model answer
Concentration is directly proportional to the mass of solute, so doubling the mass doubles the concentration.
2
Water is added to a solution without adding any more solute. Explain what happens to the concentration.
Model answer
The concentration falls, because the same mass of solute is now spread through a larger volume of solution.
3
State the relationship between the mass of solute, the volume of solution and the concentration in g/dm³.
Model answer
Concentration in g/dm³ equals the mass of solute in grams divided by the volume of the solution in dm³.
4
Calculate the mass of sodium hydroxide, relative formula mass 40, needed to make 250 cm³ of solution of concentration 2.00 mol/dm³.
Model answer
2.00 × 0.250 = 0.500 mol, and 0.500 × 40 = 20.0 g, given to 3 significant figures.
5
Calculate the mass of potassium hydroxide, relative formula mass 56, in 50.0 cm³ of solution of concentration 0.100 mol/dm³.
Model answer
0.100 × 0.0500 = 0.00500 mol, and 0.00500 × 56 = 0.280 g, given to 3 significant figures.
6
What volume of a solution of concentration 0.500 mol/dm³ contains 0.100 mol of solute?
Model answer
0.100 ÷ 0.500 = 0.200 dm³, which is 200 cm³, given to 3 significant figures.

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Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

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BKI, because potassium loses one electron and iodine gains one.

CCaCl₂, because a calcium atom loses two electrons and each chlorine atom gains one.

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