The gaseous hydrogen halides $\text{HCl}$, $\text{HBr}$ and $\text{HI}$ can be made by reacting the matching sodium salt with anhydrous phosphoric(V) acid, $\text{H}_3\text{PO}_4$. When the sodium halide $\text{NaX}$ was employed, the reaction below took place and a sample of gaseous $\text{HX}$ was collected in a gas jar.
$
\text{NaX} + \text{H}_3\text{PO}_4 \rightarrow \text{NaH}_2\text{PO}_4 + \text{HX}
$
A hot glass rod was then inserted into the sample of $\text{HX}$ and a red/orange colour appeared at once.
(a)[1]
What is the identity of $\text{NaX}$?
(b)[1]
What gas, other than $\text{HX}$, would be made if concentrated sulfuric acid was used with $\text{NaX}$ rather than phosphoric(V) acid?
(c)[1]
Suggest why phosphoric(V) acid rather than concentrated sulfuric acid is used to make samples of $\text{HX}$ from the corresponding sodium salt. Explain your answer.
Worked solution & mark scheme
This 3-mark question has a full step-by-step worked solution and mark scheme. One marking point: “sodium bromide, $NaBr$” …