Elements, Compounds and Mixtures | OCR GCSE Chemistry A, Foundation tier (J248)

Elements, Compounds and Mixtures

253 questions
17 subtopics
Paper 1
Paper 1

Elements, Compounds and Mixtures is examined in Chemistry A Paper 1.

It covers 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, nanoparticles: size and surface area to volume and uses and risks of nanoparticulate materials.

Sample questions from Elements, Compounds and Mixtures

Answer each one closed book first, then open the answer.

Purity, and melting point data

A sample contains nothing but copper atoms. Is it an element, a compound or a mixture, and is it pure?

Show the answer
It is an element, and it is pure because only one kind of atom is present.
Formulations, and separating mixtures

Why do the proportions of the components in a formulation matter so much?

Show the answer
Because the properties of the finished product depend on the proportions, so changing them gives a product that behaves differently.
Interpreting chromatograms and Rf values

A substance has an Rf value of 0.60 and the solvent front moved 10.0 cm. How far did the spot move?

Show the answer
It moved 6.0 cm, because 0.60 × 10.0 = 6.0.
Metals and non-metals in the Periodic Table

How does a non-metal oxide behave when it dissolves in water?

Show the answer
It is acidic and gives a solution with a pH below 7.
Ionic, covalent and metallic bonding compared

Which types of substance contain covalent bonds?

Show the answer
Simple molecular substances, giant covalent structures and polymers all contain covalent bonds.
Reactions, electron arrangement and Mendeleev's table

An atom has the electron arrangement 2,8,7. Predict how it will react and what ion it will form.

Show the answer
It will gain one electron to complete its outer shell, forming an ion with a single negative charge.
Diamond, graphite, fullerenes and graphene

Describe the structure of graphite.

Show the answer
It is a giant covalent structure in which each carbon atom bonds to three others, forming flat layers of hexagonal rings held to each other only by weak forces.
Bulk properties of ionic, molecular and giant structures

Explain why many simple molecular substances are gases or liquids at room temperature.

Show the answer
Because only weak intermolecular forces hold their molecules together, and these are overcome at low temperatures.

The 17 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Purity, and melting point data	What pure means to a chemist and in everyday speech, orange juice and spring water as mixtures, why chemists need the strict definition, and how a sharp melting point shows purity.	17
Relative formula mass and empirical formulae	What relative atomic, molecular and formula mass mean, calculating relative formula masses such as CO₂ and Ca(OH)₂, why the totals balance on both sides of an equation, what an empirical formula is, and working out empirical and molecular formulae from molecules, models, diagrams and relative formula mass.	16
Formulations, and separating mixtures	What a formulation is and why it is never pure, examples such as paints, medicines and brass, the jobs of the pigment and solvent in a paint, why proportions matter and alloys are harder than pure metals, and how filtration, crystallisation, simple distillation and fractional distillation separate mixtures.	15
Paper and thin layer chromatography	How a paper chromatogram is set up with a pencil baseline above the solvent, what a thin layer plate is made of and its advantage over paper, choosing a solvent, revealing colourless spots with a locating agent or ultraviolet light, the stationary and mobile phases in paper and thin layer chromatography, and why substances separate.	16
Interpreting chromatograms and Rf values	What an Rf value means, the formula and where the distances are measured from, worked Rf calculations, why Rf never exceeds 1, why the solvent must match, and reading purity and identity from a chromatogram.	15
Choosing a purification method	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.	16
Metals and non-metals in the Periodic Table	The typical physical properties of metals and non-metals, the ions each forms and why, metal oxides as basic and non-metal oxides as acidic, graphite as a non-metal that conducts, where metals and non-metals sit in the Periodic Table, why metallic character increases down a group, the elements beside the stepped line, and predicting ion charges from outer electrons.	16
Electron arrangement and position in the Periodic Table	What the group and period numbers say about electron shells, reading a position from an arrangement such as 2,8,1, atomic number and electrons, ordering by atomic number, and why Group 0 sits at the right.	11
Ionic, covalent and metallic bonding compared	The bonding and arrangement of particles in ionic compounds, simple molecules, giant covalent structures, polymers and metals, which kinds of atom each type of bonding joins, electron transfer and sharing, the electrostatic attractions that hold ionic, covalent and metallic bonds together, the ions in sodium chloride and magnesium oxide, and why atoms bond at all.	16
Dot and cross diagrams, and the limits of models	Why dots and crosses are used, the diagrams for hydrogen chloride, oxygen, methane, sodium chloride and magnesium oxide, and what dot and cross, ball and stick and flat drawings each fail to show.	16
Reactions, electron arrangement and Mendeleev's table	Why a group reacts alike, the reactivity trends in Groups 1, 7 and 0, predicting how an atom with 2,8,7 reacts, how Mendeleev ordered the elements and left gaps, and ordering by atomic number.	15
Carbon's four bonds, and the variety of organic compounds	Why a carbon atom forms four covalent bonds and never five, how many bonds remain after a double bond, why carbon forms so many compounds in chains, branches and rings, homologous series such as the alkanes, ring structures, compounds with the same formula but different properties, and natural and synthetic organic compounds.	14
Diamond, graphite, fullerenes and graphene	The structures of diamond and graphite, why diamond is hard and does not conduct while graphite is soft, slippery and conducting, what graphene is and why it is strong, light and conducting, what a fullerene is, buckminsterfullerene C₆₀, and why fullerenes melt at far lower temperatures than diamond.	11
Bond strength, intermolecular forces and predicting state	Why simple molecular substances melt and boil at low temperatures without breaking covalent bonds, why ionic compounds, giant covalent structures and metals have high melting points, why boiling points rise as molecules get larger, and predicting whether a substance is a solid, liquid or gas at a given temperature from its melting and boiling points.	16
Bulk properties of ionic, molecular and giant structures	Why bulk properties belong to many atoms rather than one, why ionic compounds conduct only when molten or dissolved and are brittle, why simple molecular substances are often gases or liquids and do not conduct, why metals are malleable and conduct, why giant covalent structures are insoluble, why polymers soften on heating, and identifying a structure from its properties.	11
Nanoparticles: size and surface area to volume	The size range of nanoparticles, nanometres in metres, how many atoms or molecules fit across one, why they cannot be seen with a light microscope, calculating the surface area to volume ratio of cubes and how it changes as particles get smaller, and why nanoparticles make effective catalysts, react faster and behave differently from the bulk material.	16
Uses and risks of nanoparticulate materials	Uses of nanoparticles in sun creams, wound dressings, catalysts, sports equipment, self-cleaning glass, electronics and medicine delivery, why their colour can differ from the bulk, and the risks of them entering cells, lungs and the bloodstream, harming river bacteria and being highly reactive, with the uncertain long-term effects, the limits of ordinary safety tests and the case for labelling.	16

Elements, Compounds and Mixtures is 253 of the 1,070 questions in the guide.Get the guide, £7

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.