Reactivity of Metals, Acids, and Electrolysis

Vocabulary flashcards reviewing concepts of oxidation and reduction, reactivity of metals, acid reactions, pH, salt preparation, and electrolysis rules and equations.

Oxidation (oxygen transfer)

When a substance gains oxygen.

Reduction (oxygen transfer)

When a substance loses oxygen.

Reactivity series of metals

A series that shows metals in order of their reactivity. Metals above $H_2$ react with acid to produce $H_2$, whereas metals below $H_2$ do not react with acids. Not all metals above $H_2$ react with water (mostly Group I and II metals, with aluminium being borderline).

Displacement reaction

A reaction where a more reactive metal displaces a less reactive metal from a compound.

Reduction with carbon

A method used to extract metals less reactive than carbon, where carbon displaces the metal in a metal oxide, oxidising carbon to carbon oxides and reducing the metal oxide to pure metal.

Oxidation (electron transfer)

Loss of electrons.

Reduction (electron transfer)

Gain of electrons.

Metal and acid reaction

A redox reaction and displacement reaction represented by the general equation: $\text{Metal} + \text{acid} \rightarrow \text{salt} + \text{hydrogen}$.

Metal carbonate and acid reaction

A reaction represented by the general equation: $\text{Metal carbonate} + \text{acid} \rightarrow \text{salt} + \text{water} + \text{carbon dioxide}$.

Metal oxide and acid reaction

A reaction represented by the general equation: $\text{Metal oxide} + \text{acid} \rightarrow \text{salt} + \text{water}$.

Magnesium and hydrochloric acid redox transfer

Magnesium is oxidised by losing electrons ($Mg \rightarrow Mg^{2+}$) and hydrogen in $HCl$ is reduced by gaining electrons ($H^+ \rightarrow H_2$).

Soluble salt preparation

A three-step method: a) React the excess acid with some insoluble chemical (e.g., metal oxide); b) Filter off the leftovers; c) Crystallise the product.

Base

Compounds that neutralise acids.

Acid

Substances that produce hydrogen ions in aqueous solutions.

Alkali

Soluble bases that produce hydroxide ions in aqueous solutions.

pH scale

The measure of acidity or alkalinity of a solution, where a pH of $7$ indicates a neutral solution.

Neutralisation reaction (ionic equation)

$$H^+ + OH^- \rightarrow H_2O$$

Strong acid

An acid that is completely ionised in aqueous solution.

Weak acid

An acid that is only partially ionised in aqueous solution.

Concentrated acid

An acid solution that contains more moles of acid per unit volume compared to a dilute acid solution.

pH and hydrogen ion concentration relationship

As the pH decreases by one unit, the hydrogen ion concentration increases by a factor of $10$.

$$LiNO_3$$

Lithium nitrate

$$K_2CO_3$$

Potassium carbonate

$$MgBr_2$$

Magnesium bromide

$$BaSO_4$$

Barium sulfate

Electrolysis

The passing of an electric current through ionic substances that are molten or in solution to break them down into elements, occurring as ions are discharged (lose or gain electrons) at electrodes.

Cathode

The negative electrode where reduction occurs during electrolysis.

Anode

The positive electrode where oxidation occurs during electrolysis.

Discharge rules in aqueous electrolysis

At the cathode, hydrogen is produced unless a less reactive metal is present. At the anode, oxygen is produced unless the solution contains halide ions, in which case halogen molecules are produced.

Cryolite

A compound used in the manufacturing of aluminium to lower the melting point of aluminium oxide, thereby reducing energy costs.

Electrolysis of aluminium oxide (half equations)

Cathode: $Al^{3+} + 3e^- \rightarrow Al$; Anode: $2O^{2-} \rightarrow O_2 + 4e^-$, with oxygen subsequently reacting with the carbon anode to produce $CO_2$.

Electrolysis of aqueous $Na_2SO_4$ (half equations)

Cathode: $2H^+ + 2e^- \rightarrow H_2$; Anode: $4OH^- \rightarrow 2H_2O + O_2 + 4e^-$.

Electrolysis of molten $KCl$ (half equations)

Cathode: $K^+ + e^- \rightarrow K$; Anode: $2Cl^- \rightarrow Cl_2 + 2e^-$.

Electrolysis of aqueous $KCl$ (half equations)

Cathode: $2H^+ + 2e^- \rightarrow H_2$; Anode: $2Cl^- \rightarrow Cl_2 + 2e^-$.

Electrolysis of aqueous $CuBr_2$ (half equations)

Cathode: $Cu^{2+} + 2e^- \rightarrow Cu$; Anode: $2Br^- \rightarrow Br_2 + 2e^-$.