Chemical Changes

What happens when metals react with oxygen?

They form metal oxides.

What is oxidation in terms of oxygen?

Gain of oxygen.

What is reduction in terms of oxygen?

Loss of oxygen.

What is the reactivity series from most to least reactive?

Potassium - sodium - lithium - calcium - magnesium - carbon - zinc - iron - hydrogen - copper.

Why are carbon and hydrogen included in the reactivity series?

They help predict metal extraction + reactions of metals with acids.

How is metal reactivity linked to ion formation?

More reactive metals form positive ions more easily.

How do potassium, sodium and lithium react with water?

React vigorously - produce metal hydroxide + hydrogen.

What is the general equation for a metal reacting with water?

Metal + water - metal hydroxide + hydrogen.

How does calcium react with water?

Reacts readily - produces calcium hydroxide + hydrogen.

How does magnesium react with cold water?

Very slowly.

How do zinc, iron and copper react with cold water?

Little or no reaction under the conditions required by AQA.

How do magnesium, zinc and iron react with dilute acids?

Metal + acid - salt + hydrogen.

Does copper react with dilute hydrochloric or sulfuric acid?

No - copper is below hydrogen in the reactivity series.

Why do metals above hydrogen react with dilute acids?

They are more reactive than hydrogen and displace it from the acid.

What is a displacement reaction?

A more reactive element displaces a less reactive element from its compound.

Can magnesium displace copper from copper sulfate?

Yes - magnesium is more reactive than copper.

Can copper displace magnesium from magnesium sulfate?

No - copper is less reactive than magnesium.

How can experimental reactions be used to determine a reactivity series?

More vigorous/easier reactions indicate greater reactivity.

What is oxidation in terms of electrons?

Loss of electrons. (HT)

What is reduction in terms of electrons?

Gain of electrons. (HT)

How can you remember oxidation and reduction with electrons?

OIL RIG - Oxidation Is Loss, Reduction Is Gain. (HT)

What happens to a metal atom when it forms a positive ion?

It loses electrons - it is oxidised. (HT)

What happens when a positive metal ion becomes a metal atom?

It gains electrons - it is reduced. (HT)

What is a redox reaction?

Reaction where oxidation + reduction happen at the same time.

What is an ionic equation?

Equation showing only the particles directly involved in a reaction. (HT)

What happens to spectator ions in an ionic equation?

They are omitted because they do not change. (HT)

How are metals less reactive than carbon usually extracted from their oxides?

Reduction using carbon.

Why can carbon extract some metals from their oxides?

Carbon is more reactive than those metals - it removes oxygen from their oxides.

How are metals more reactive than carbon extracted?

Electrolysis of molten compounds.

Why is electrolysis needed for metals above carbon?

Carbon cannot reduce their compounds because the metals are more reactive than carbon.

Why are very unreactive metals sometimes found as pure elements?

They do not react readily with other elements.

What is bioleaching?

Using bacteria to produce solutions containing metal compounds from low-grade ores. (Chemistry only)

What is phytomining?

Plants absorb metal compounds - plants are harvested + burned - metal is extracted from the ash. (Chemistry only)

Why can bioleaching and phytomining be useful?

Allow extraction from low-grade ores with less traditional mining. (Chemistry only)

What is a disadvantage of biological metal extraction?

It can be slow + may produce relatively small quantities.

What is produced when an acid reacts with a metal?

Salt + hydrogen.

What is produced when an acid reacts with a metal oxide?

Salt + water.

What is produced when an acid reacts with a metal hydroxide?

Salt + water.

What is produced when an acid reacts with an alkali?

Salt + water.

What is produced when an acid reacts with a metal carbonate?

Salt + water + carbon dioxide.

What salt does hydrochloric acid produce?

Chloride salts.

What salt does nitric acid produce?

Nitrate salts.

What salt does sulfuric acid produce?

Sulfate salts.

How do you determine the metal in the salt name?

It comes from the metal/base/carbonate reacting with the acid.

What salt forms from magnesium + hydrochloric acid?

Magnesium chloride + hydrogen.

What salt forms from copper oxide + sulfuric acid?

Copper sulfate + water.

What salt forms from calcium carbonate + nitric acid?

Calcium nitrate + water + carbon dioxide.

RP1 - What is the aim of the soluble salt practical?

Prepare a pure, dry sample of a soluble salt from an insoluble oxide or carbonate.

RP1 - Why is the dilute acid warmed?

Increases reaction rate.

RP1 - Why should the acid not be boiled?

Reduces risk of acid spraying + excessive evaporation.

RP1 - How is an insoluble solid added to the acid?

Add small portions while stirring until some solid remains unreacted.

RP1 - Why is excess insoluble solid added?

Ensures all the acid has reacted.

RP1 - How is excess solid removed?

Filter the mixture - excess solid remains as residue.

RP1 - What is in the filtrate after filtering?

Salt solution.

RP1 - How is the salt solution concentrated?

Heat gently to evaporate some water.

RP1 - Why should all the water not be evaporated immediately?

Crystals should form by crystallisation as the concentrated solution cools.

RP1 - How are crystals obtained?

Allow concentrated solution to cool - crystals form.

RP1 - How are the crystals made pure and dry?

Filter crystals - wash with a little distilled water - dry between filter papers/in a warm place.

RP1 - What is the full method for making a soluble salt?

Warm acid - add excess insoluble solid - filter - evaporate some water - cool to crystallise - filter + dry crystals.

What ions do acids produce in aqueous solution?

H+ ions.

What ions do alkalis produce in aqueous solution?

OH- ions.

What does the pH scale measure?

Acidity or alkalinity of a solution.

What is the pH range normally used?

0-14.

What pH is neutral?

pH 7.

What pH values are acidic?

Less than 7.

What pH values are alkaline?

Greater than 7.

How can approximate pH be measured?

Universal indicator/wide-range indicator.

How can pH be measured more accurately?

pH probe/meter.

What happens during neutralisation between an acid and alkali?

H+ ions react with OH- ions to form water.

What is the ionic equation for neutralisation?

H+ + OH- - H2O.

What is a strong acid?

Acid that completely ionises in aqueous solution. (HT)

What is a weak acid?

Acid that only partially ionises in aqueous solution. (HT)

Give examples of strong acids required at GCSE.

Hydrochloric acid, nitric acid + sulfuric acid.

Give an example of a weak acid.

Ethanoic acid.

What is the difference between strong and concentrated?

Strong describes degree of ionisation - concentrated means large amount of acid per unit volume.

What is the difference between weak and dilute?

Weak means partially ionised - dilute means small amount of acid per unit volume.

Can a dilute acid be strong?

Yes - strength and concentration are different properties.

How does H+ concentration change when pH decreases by 1?

H+ concentration increases by a factor of 10. (HT)

How does H+ concentration change when pH increases by 1?

H+ concentration decreases by a factor of 10. (HT)

How much greater is H+ concentration at pH 2 than pH 4?

100 times greater - two pH units = 10 x 10. (HT)

For acids of the same concentration, which has the lower pH - strong or weak?

Strong acid - more ionised so higher H+ concentration. (HT)

What is a titration used for?

Accurately determine the volume of acid that reacts with a known volume of alkali or vice versa. (Chemistry only)

RP2 - What equipment accurately measures a fixed volume of solution?

Volumetric pipette + pipette filler.

RP2 - What equipment accurately delivers a variable volume during titration?

Burette.

RP2 - What container is normally used for the reacting solution?

Conical flask.

RP2 - Why is a conical flask used?

It can be swirled without easily spilling the solution.

RP2 - How do you carry out a titration?

Pipette known volume into conical flask - add indicator - record burette reading - add other solution while swirling - near endpoint add dropwise - record final burette reading.

RP2 - How is titre calculated?

Final burette reading - initial burette reading.

RP2 - What is the endpoint?

Point where indicator just permanently changes colour.

RP2 - Why is solution added dropwise near the endpoint?

Prevents overshooting + improves accuracy.

RP2 - What is a rough titration used for?

Estimate the endpoint so later titrations can approach it accurately.

RP2 - What are concordant titres?

Titres that are very close together - usually within about 0.10 cm³.

RP2 - Which titres should be used to calculate the mean?

Concordant titres - do not include the rough titre.

RP2 - Why is a white tile placed under the flask?

Makes the indicator colour change easier to see.

RP2 - Why should a pipette filler be used?

Never pipette by mouth - prevents contact with corrosive solutions.

How do you convert a titration volume from cm³ to dm³?

Divide by 1000.

How do you calculate moles from concentration and volume?

Moles = concentration (mol/dm³) x volume (dm³). (HT)

What is the method for a titration calculation?

Convert volume to dm³ - calculate known moles - use balanced equation mole ratio - calculate unknown concentration. (HT)

How do you calculate concentration in mol/dm³?

Concentration = moles / volume in dm³. (HT)

How can concentration in g/dm³ be found from mol/dm³?

Concentration (g/dm³) = concentration (mol/dm³) x Mr. (HT)