molar mass - acid base problem -chemistry (9.11)

Question

100ml of a solution containing 0.081 g of a strong acid HA has a pH=2. What is the chemical formula of the strong acid?

A. HF

B. HCl

C. HBr (the answer)

D. HI

so I came up with;

Mr(HA)=0.081g/n(HA)

therefore, we need to find mol of HA.

please help me figure out what to do after this.

Answer 1

To find the chemical formula of the strong acid, you would need to find molar mass.

Molar mass = grams / moles

We solve for the moles by getting the concentration (Molarity) of HA.

To do that use the equation 10^-pH = [H⁺]

10^-2 = 0.01 M

Use volume to solve for the moles of the strong acid

100 mL x 1 L x 0.01 moles acid = 0.001 moles of acid

1000mL 1L

Molar mass = 0.081g

0.001 moles

Molar mass of the acid = 81 g/mol

So the strong acid that has that molar mass from the choices is HBr.