Two liquids mix completely and boil at 78 °C and 100 °C. Which technique separates them?

Fractional distillation, because they have different boiling points but are close enough to need a fractionating column.

What property of the components must differ for any kind of distillation to work?

Their boiling points must be different.

What difference in properties does filtration rely on?

It relies on one component being insoluble in the liquid while the other is a liquid or is dissolved in it.

OCR GCSE Combined Science Chemistry J250

Chemical Reactions

Topic overview Writing formulae of elements and compounds Balanced equations, and deducing formulae from ions State symbols in equations Conservation of mass, and changes of mass in open systems Exothermic and endothermic reactions, and reaction profiles Activation energy and why reactions need it Oxidation and reduction in terms of oxygen Acids, alkalis and neutralisation The ionic equation for neutralisation, and reactions of acids The pH scale, acidity and alkalinity Measuring pH with indicators and pH meters 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 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 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 Activation energy, and enzymes as catalysts

Particles

Topic overview The particle model and changes of state 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

Elements, Compounds and Mixtures

Choosing a purification method

3 things to know
Paper 3 (Chemistry)

Overview

Matching filtration, simple distillation, crystallisation and fractional distillation to mixtures, the property each relies on, purifying rock salt, choosing paper or thin layer chromatography, and how gas chromatography works.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Which technique would you suggest to separate sand from water, and why?

Key term

Which technique would you suggest to obtain pure water from seawater?

Key term

Which technique would you suggest to obtain solid copper sulfate from copper sulfate solution?

Questions from this subtopic

Each one with the model answer underneath.

1
Which technique would you suggest to separate sand from water, and why?
Model answer
Filtration, because sand is insoluble and stays on the filter paper while the water passes through.
2
Which technique would you suggest to obtain pure water from seawater?
Model answer
Simple distillation, because the water evaporates and is condensed while the dissolved salts are left behind.
3
Which technique would you suggest to obtain solid copper sulfate from copper sulfate solution?
Model answer
Crystallisation, because the solid is soluble and forms crystals as the solution is concentrated and cooled.
4
Two liquids mix completely and boil at 78 °C and 100 °C. Which technique separates them?
Model answer
Fractional distillation, because they have different boiling points but are close enough to need a fractionating column.
5
What property of the components must differ for any kind of distillation to work?
Model answer
Their boiling points must be different.
6
What difference in properties does filtration rely on?
Model answer
It relies on one component being insoluble in the liquid while the other is a liquid or is dissolved in it.

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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.

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