Question

multiple choice 10 points
which of the following is the correct formula for the following name: arsenous acid
$\ce{h_{3}aso_{3}}$
$\ce{h_{3}aso_{4}}$
$\ce{h_{3}aso}$
$\ce{h_{3}as}$

Explanation:

Step1: Recall acid naming rules

Acids with -ous suffix have lower oxidation state of central atom. Arsenous acid has As in +3 oxidation state.

Step2: Check oxidation states

• For \(H_3AsO_3\): Let oxidation state of As be \(x\). Using \(3\times(+ 1)+x + 3\times(-2)=0\), we get \(x = +3\).
• For \(H_3AsO_4\): \(3\times(+1)+x + 4\times(-2)=0\), \(x=+5\) (arsenic acid).
• For \(H_3AsO\): \(3\times(+1)+x+(-2)=0\), \(x=-1\) (not valid as per common acid structures).
• For \(H_3As\): It is arsine, not an acid (no oxygen in formula for an oxy - acid as implied by the name ending with -ous acid).

Answer:

\(H_3AsO_3\) (first option)