Separate Chemistry 1

What are typical properties of transition metals?

High melting points, high density, formation of coloured compounds and catalytic activity of the metals and their compounds.

What is an example of a transition metal that shows catalytic activity?

Iron and its compounds.

What is corrosion?

The oxidation of a metal.

What is rusting?

The corrosion of iron caused by its reaction with oxygen and water.

How can rusting of iron be prevented by excluding oxygen?

By preventing oxygen from reaching the iron, for example by painting or oiling it.

How can rusting of iron be prevented by excluding water?

By preventing water from reaching the iron, for example by keeping it dry or using a protective coating.

What is sacrificial protection?

Protecting iron by attaching a more reactive metal to it, which oxidises instead of the iron.

Why does sacrificial protection work?

The more reactive metal loses electrons and corrodes instead of the iron.

What is electroplating?

Coating a metal object with a thin layer of another metal using electrolysis.

Why is electroplating used?

To improve the appearance of an object and/or increase its resistance to corrosion.

Why are alloys generally stronger than pure metals?

Different-sized atoms in an alloy distort the regular layers of atoms, making it harder for the layers to slide over each other.

Why is iron alloyed with other metals?

To produce alloy steels with improved properties such as greater strength, hardness or corrosion resistance.

What are the uses of aluminium related to?

Its low density, corrosion resistance and strength when alloyed.

What are the uses of copper related to?

Its excellent electrical conductivity, ductility and resistance to corrosion.

What are the uses of gold related to?

Its low reactivity, resistance to corrosion and attractive appearance.

What is magnalium?

An alloy of aluminium and magnesium that is stronger than pure aluminium while remaining relatively lightweight.

What is brass?

An alloy of copper and zinc that is harder than pure copper.

How is concentration in mol dm⁻³ calculated?

Concentration (mol dm⁻³) = moles ÷ volume (dm³).

How can concentration in g dm⁻³ be converted to mol dm⁻³?

Concentration (mol dm⁻³) = concentration (g dm⁻³) ÷ relative formula mass.

How can concentration in mol dm⁻³ be converted to g dm⁻³?

Concentration (g dm⁻³) = concentration (mol dm⁻³) × relative formula mass.

What apparatus is used for an accurate acid-alkali titration?

A burette, pipette and suitable indicator.

What is the purpose of a burette in titration?

To accurately measure and deliver a variable volume of solution.

What is the purpose of a pipette in titration?

To accurately measure a fixed volume of solution.

What is the purpose of an indicator in titration?

To show when the acid and alkali have reacted in the correct proportions.

What can titration results be used to calculate?

An unknown concentration or an unknown volume of a solution.

What is percentage yield?

Percentage yield = (actual yield ÷ theoretical yield) × 100.

Why is the actual yield usually less than the theoretical yield?

Because reactions may be incomplete, material can be lost during the experiment, and competing side reactions may occur.

What is atom economy?

A measure of how much of the reactants' mass is converted into the desired product.

How is atom economy calculated?

Atom economy = (Mr of desired product ÷ total Mr of reactants) × 100.

Why is a high atom economy desirable?

It produces less waste because a greater proportion of the reactants becomes the desired product.

What factors can affect the choice of a reaction pathway?

Atom economy, yield, rate, equilibrium position and usefulness of by-products.

What is the molar volume of a gas at room temperature and pressure?

24 dm³ per mole, or 24,000 cm³ per mole.

How can the volume of a gas be calculated using molar volume?

Volume = moles × 24 dm³ at room temperature and pressure.

How can moles of a gas be calculated using molar volume?

Moles = volume ÷ 24 dm³ at room temperature and pressure.

What can molar volume and balanced equations be used to calculate?

The masses of solids and volumes of gases involved in reactions.

What is Avogadro's law?

Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

How can Avogadro's law be used in gaseous reactions?

Gas volumes can be compared using the mole ratios in the balanced chemical equation.

What is the Haber process?

An industrial reversible reaction between nitrogen and hydrogen to produce ammonia.

What is the equation for the Haber process?

N₂ + 3H₂ ⇌ 2NH₃.

How does increasing temperature affect the rate at which equilibrium is reached?

It increases the rate of both forward and reverse reactions, so equilibrium is reached faster.

How does increasing pressure affect the rate at which equilibrium is reached?

It increases the frequency of collisions between particles, so equilibrium is reached faster.

How does increasing concentration affect the rate at which equilibrium is reached?

It increases the frequency of collisions, so equilibrium is reached faster.

How does a catalyst affect the rate at which equilibrium is reached?

It speeds up both the forward and reverse reactions equally, so equilibrium is reached faster.

What does a catalyst do to the position of equilibrium?

It does not change the position of equilibrium; it only makes equilibrium reached faster.

Why are industrial reaction conditions chosen carefully?

To balance the availability and cost of raw materials and energy with obtaining an acceptable yield in an acceptable time.

What factors must be considered when choosing industrial conditions?

The cost and availability of raw materials and energy, temperature, pressure, catalyst and the required yield and rate.

What elements do fertilisers commonly contain?

Nitrogen, phosphorus and potassium.

Why are nitrogen, phosphorus and potassium compounds used in fertilisers?

They provide nutrients needed to promote plant growth.

What is produced when ammonia reacts with nitric acid?

Ammonium nitrate, which is used as a fertiliser.

What is the equation for ammonia reacting with nitric acid?

NH₃ + HNO₃ → NH₄NO₃.

How is ammonium sulfate prepared in the laboratory?

Ammonia solution is reacted with dilute sulfuric acid in the correct proportions, then the solution is concentrated and crystals are obtained.

How does industrial ammonium sulfate production differ from laboratory preparation?

Industrial production occurs on a much larger scale and requires several stages to produce the ammonia and sulfuric acid from their raw materials.

What is a chemical cell?

A cell that produces a voltage until one of its reactants is used up.

What happens to the voltage of a chemical cell when a reactant is used up?

The cell eventually stops producing a voltage.

What happens in a hydrogen-oxygen fuel cell?

Hydrogen and oxygen react to produce a voltage, with water as the only product.

What is the overall product of a hydrogen-oxygen fuel cell?

Water.

What are advantages of hydrogen-oxygen fuel cells?

They produce electricity efficiently and water is the only product, so there are no carbon dioxide emissions at the point of use.

What are disadvantages of hydrogen-oxygen fuel cells?

Hydrogen can be difficult to store and transport, fuel cells can be expensive, and producing hydrogen may require energy.

How should the suitability of a fuel cell for a particular use be evaluated?

By weighing its advantages and disadvantages, including efficiency, emissions, cost, hydrogen storage and availability.