topic 4 chemical changes

What are the products of the following reaction acid + alkali?

salt + water

what’s a strong acid

Strong acids ionise completely in water - all acid particles dissociate to release H+ ions.

What are weak acids?

Weak acids are ones that only partially ionise in water.

Write out the reactivity series:

Potassium Sodium Lithium Calcium Magnesium Aluminium Carbon Zinc Iron Tin Hydrogen Copper Silver Gold

What is the chemical formula for nitric acid?

HNO₃

What is the chemical formula for carbonic acid?

H₂CO₃

What colour does universal indicator change to in the presence of a neutral substance?

green

What is the chemical formula for sulfuric acid?

H₂SO₄

What are the products of an acid + a carbonate?

salt + water + carbon dioxide

What are the products of acid + base?

salt + water

What are the products of metal + acid?

salt + hydrogen

What is the mnemonic for remembering the reactivity series?

Please Send Little Charlie Monkeys And Cute Zebras In To Hot Countries Signed Gordon

What is an ore?

An ore is a rock that contains enough of a metal or a metal compound to make extracting the metal worthwhile.

What is electrolysis?

Electrolysis involves using electricity to break down an ionic compound (called the electrolyte) to form elements.

What is the substance getting broken down in electrolysis called?

electrolyte

What colour does universal indicator change to in the presence of an acid?

red

For electrolysis to take place why does the electrolyte have to be aqueous or liquid?

In electrolysis the ions carry electrical charge through the substance. The ions have to be able to move freely through the substance and for them to do that they must be molten or dissolved.

Why do the electrodes used in electrolysis have to be inert?

To avoid any unwanted chemical reactions of the products with the electrodes.

What is an inert electrode?

Inert electrodes do not participate in the reactions and just provide a surface area for the reaction and electron swapping to occur.

What are the rules for determining which element will get produced at the cathode?

The less reactive element gets produced at the cathode. If it is more reactive than hydrogen then hydrogen will be produced.

What are the rules for determining which element will get produced at the anode?

If a halide is present then a halogen is formed. If no halide ions are present then hydroxide ions are discharged and oxygen is formed.

What is the equation showing hydroxide ions being discharged at the anode?

4OH → 2H₂O + O₂

What is the name of the ore that is made up of aluminium oxide?

Bauxite.

What is the melting point of aluminium oxide?

Over 2,000°C.

What would you use to measure the pH of a substance electronically?

A pH probe attached to a pH meter.

What is the name of the aluminium compound that aluminium oxide gets mixed with to decrease its melting point?

Cryolite.

Write is the formula for aluminium oxide?

Al₂O₃

What is the half equation showing the products at the negative electrode of the electrolysis of aluminium oxide?

Al³⁺_(l) + 3e^- > Al_(s)

Why do the electrodes during the electrolysis of aluminium oxide constantly have to be replaced?

• The anodes used during the electrolysis of aluminium oxide are made up of graphite (carbon) and the oxygen produced during electrolysis reacts with the electrode to produce carbon dioxide gas.

• This means that the carbon anodes gradually burn away and have to be replaced regularly.

Why is electrolysis expensive?

Melting the compounds such as aluminium oxide requires lots of energy.
A lot of energy is required to produce the electric current.

What is the half equation at the anode in the electrolysis of aluminium oxide?

2O^2--> 2O₂+ 4e^-

What is the difference between the processes in electrolysis and a fuel cell?

Electrolysis uses electricity to produce a chemical reaction but cells use a chemical reaction to produce electricity.

Why is graphite used for the electrodes?

• Graphite conducts electricity.

• Graphtie is inert.

What colour does universal indicator change to in the presence of an alkali?

Purple.

What is an electrolyte?

An ionic compound that is molten or dissolved in water and can conduct electricity.

How is aluminium extracted after aluminium ions become reduced?

The molten aluminium sinks to the bottom of the cell where it is tapped off.

What is the half equation for hydroxide ions being discharged at the anode?

4OH^- -> 2H₂O + O₂ + 4e^-

What is brine?

Brine is a solution of sodium chloride and water.

What are the uses of chlorine from the electrolysis of brine?

• Can be used as a disinfectant due to its antibacterial properties.

• Can be used to manufacture bleach.

What are the uses of hydrogen from the electrolysis of brine?

• Can be used to manufacture hydrochloric acid.

• Can be used as a pollution-free fuel for hydrogen-fuel cells.

What are the uses of sodium hydroxide from the electrolysis of brine?

• Sodium hydroxide is a common cleaning product and is often used to clean ovens and unblocking drains.