Question

a solution containing 3.76 g naoh in 361 ml water is titrated to the endpoint with 491 ml hcl. what is the molar concentration of hcl in the original solution? a. 0.13 b. 130 c. 0.0031 d. 0.00053 e. 0.19

Answer 1

The molar concentration of HCl in the original solution is 0.19

The balanced chemical equation for the reaction must be our starting point because it will provide us with the reactants' mole ratios and allow us to answer this question.

* NaOH + HCl --> NaCl + H2O

this means:

1 mole NaOH reacts with 1 mole HCl

thus the ratio of NaOH to HCl is 1: 1

Next we've got to calculate the moles of NaOH: (molecular Mass = 40 g/mol)

moles(NaOH) = 3.76g/40

= 0.094 moles

Now we can calculate the concentration of NaOH:

Note: 361mL/1000 = 0.361L

conc(NaOH) = 0.094 moles/0.361L

= 0.26 mol/L

Now the mole ratio of NaOH to HCl is 1:1

But we have used only 0.094 moles so since the ratio of NaOH to HCl is 1:1, it means that 0.094moles of NaOH can only react with 0.094 moles of HCl.

Note: 491mL/1000mL = 0.491L

conc(HCl) = 0.094 moles/0.491L

= 0.19 mol/L

Thus the molar concentration of HCl in the original solution is 0.19

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