A 100mL sample of hydrobromic acid, HBr, is titrated to an endpoint with 24.0mL of 1.5 N NaOH.?

Question

What is the concentration of HBr?

1.4 N

0.72 N

3.1 N

0.36 N

Answer 1

Equivalents NaOH = 24.0 x 1.5 / 1000 = 0.036 = equivalents HBr
N = 0.036 / 0.100 L = 0.36

Answer 2

First write down the reaction formula.

HBr + NaOH = NaBr + H2O
Notice that all the chemicals in the reaction scheme are in the ration of 1 : 1 :: 1: 1

Next calculate the mole of NaOH used.
mol(NaOH) = (1.5 x 24)/1000
mol (NaOH) = 0.036 mol.

From the reaction formula we note all the reactants are in the ration of 1 : 1
So mol(NaOH) = mol(HBr) = 0.036

So going back to our calculation format (template) above:-

0.036 = ([concHBr] x 100)/1000
and rearrange.algebraically,
[concHBr] = (0.036 x 1000)/100
conc(HBr) = 0.36 mol L^-1 = 0.36M