For the preparation of HBr in the lab the corresponding bromide salt should be treated with __________ acid.

PLACEHOLDER ANSWER - the answer is the name of an acid. Concentrated phosphoric acid is used, $$\text{NaBr} + \text{H}_3\text{PO}_4 \rightarrow \text{NaH}_2\text{PO}_4 + \text{HBr}$$. Concentrated sulphuric acid is not suitable, since it oxidises HBr to bromine, $$2\text{HBr} + \text{H}_2\text{SO}_4 \rightarrow \text{Br}_2 + \text{SO}_2 + 2\text{H}_2\text{O}$$.