Quick questions on Volumetric analysis and titration: VCE Chemistry Unit 2

Same workflow with a redox reaction instead of acid-base. The standard may be itself coloured (KMnO4 is intensely purple) and acts as its own indicator: the first persistent pink colour beyond the analyte signals the endpoint. Iodine titrations use starch (deep blue with I2). Acidified KMnO4 is used to titrate Fe^2+ and other reductants.

State three features that make a substance a suitable primary standard. [3 marks]

A $25.00 \, \text{mL}$ aliquot of vinegar is diluted to $250 \, \text{mL}$ in a volumetric flask. $25.00 \, \text{mL}$ aliquots of the diluted solution are titrated against $0.100 \, \text{mol/L}$ NaOH, average titre $20.50 \, \text{mL}$. Calculate the concentration of ethanoic acid in the original vinegar in g/L.

A back-titration determines $\text{NH}_3$ in a fertiliser. (a) Outline the procedure. (b) $1.000 \, \text{g}$ of fertiliser releases $\text{NH}_3$ absorbed in $50.0 \, \text{mL}$ of $0.500 \, \text{mol/L}$ HCl.