Chemical Changes

What is the general equation for the reaction of a metal with water?

Metal + Water → Metal Hydroxide + Hydrogen

Which gas is produced when a metal reacts with a dilute acid?

Hydrogen

What determines the "reactivity" of a metal?

Its tendency to form positive ions (lose electrons)

In a displacement reaction, which metal ends up as a compound?

The more reactive metal

Why are gold and platinum found as pure metals in the Earth's crust?

They are too unreactive so don’t form compounds.

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

Reduction with carbon (heating with carbon)

Define "oxidation" in terms of oxygen transfer.

The gain of oxygen

Define "reduction" in terms of electron transfer.

The gain of electrons

What is the ionic equation for a neutralisation reaction?

$H^+(aq) + OH^-(aq) \rightarrow H_2O(l)$

What are the products when an acid reacts with a metal carbonate?

Salt + Water + Carbon Dioxide

What is the difference between a "strong" acid and a "concentrated" acid?

A strong acid completely ionises in water but concentrated means there are many acid particles in the solution.

As the pH decreases by one unit, what happens to the hydrogen ion concentration?

It increases by a factor of 10

Why must a salt solution be heated gently during crystallization?

To avoid decomposing the salt or causing "spitting"

Which ions do all aqueous acids contain?

Hydrogen ions

Why can ionic compounds only be electrolysed when molten or in solution?

The ions are free to move and carry charge

During electrolysis, which electrode do the negative ions (anions) move towards?

The anode (positive electrode)

In the electrolysis of molten lead bromide, what is produced at the cathode?

Lead (Pb) metal

Why is cryolite added to aluminium oxide in the extraction of aluminium?

To lower the melting point and reduce energy costs

In the electrolysis of aqueous sodium chloride, why is hydrogen gas produced at the cathode instead of sodium?

Because sodium is more reactive than hydrogen

At the anode during aqueous electrolysis, when is oxygen gas NOT produced?

When the solution contains halide ions (Cl-, Br-, I-)

What is the half-equation for the formation of oxygen gas at the anode in an aqueous solution?

4OH- → O2 + 2H2O + 4e-