Determine the molecular formula of the compound.

Identify the fragments responsible for the peaks at

m/z = 15

m/z = 45

Identify a compound that could produce this spectrum.

\({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}{{\text{O}}_{\text{2}}}\);

No mark for (CH₂O)₂.

m/z = 15

\({\text{CH}}_3^ + \);

m/z = 45

\({\text{COO}}{{\text{H}}^ + }{\text{/C}}{{\text{O}}_{\text{2}}}{{\text{H}}^ + }{\text{/HCO}}{{\text{O}}^ + }{\text{/OCO}}{{\text{H}}^ + }\);

Penalize once if charges are missing.

ethanoic acid/ \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}\) / methyl methanoate/ \({\text{HCOOC}}{{\text{H}}_{\text{3}}}\);

Accept acetic acid.

Most candidates gave the correct molecular formula (a) and many candidates identified the fragments correctly.

Many candidates did not give the charge of the ion.

Many candidates identified acetic acid.