Quick questions on Formulae and equations - WJEC A-Level Chemistry

Ionic formulae balance the charges of the ions (for example $\text{Al}^{3+}$ and $\text{O}^{2-}$ give $\text{Al}_2\text{O}_3$). Covalent formulae follow the combining numbers of the atoms. You should know common ions such as $\text{SO}_4^{2-}$, $\text{NO}_3^-$, $\text{CO}_3^{2-}$ and $\text{NH}_4^+$.

Apply the rules in order of priority. An uncombined element is always $0$. A simple monatomic ion equals its charge. Fluorine is always $-1$; oxygen is $-2$ except in peroxides ($-1$) and with fluorine; hydrogen is $+1$ except in metal hydrides ($-1$).

The oxidation and reduction half equations you balance here describe the electrode reactions in cells, central to the electrochemistry of Unit 3. Oxidation numbers and naming. Roman numerals in names like iron(III) chloride and manganate(VII) come directly from oxidation numbers, so assigning them correctly lets you name and identify unfamiliar compounds.

State the oxidation number of sulfur in the sulfate ion $\text{SO}_4^{2-}$. [1 mark]

Write the ionic equation for the reaction of aqueous silver nitrate with aqueous sodium chloride. [1 mark]

Deduce the formula of the compound formed between calcium and nitrate ions. [1 mark]

State the oxidation number of oxygen in hydrogen peroxide, $\text{H}_2\text{O}_2$. [1 mark]

Write the ionic equation for the neutralisation of any strong acid by any strong alkali. [1 mark]