Question

A solution containing 10.0 ml of the strong acid hbr has a ph o 2.62. the weak acid is titrated with 0.124 m naoh in the presence of a ph indicator. the indicator changes coor (approximating the quivalence point) when 15.62 ml of naoh are added. what is the original concentration in m of the hf sample??

Answer 1

The original concentration of HF can be determined using the volume and molarity of NaOH at the equivalence point. By calculating the moles of NaOH and equating it to the moles of HF, and then dividing by the volume of the HF solution, the concentration of HF is found to be 0.193648 M.

Step-by-step explanation:

To determine the original concentration of the HF sample, we use the titration data. At the equivalence point, the moles of acid and base are equal. Since we know the volume and molarity of NaOH used, we can calculate the moles of NaOH, which will be equal to the moles of HF initially present.

The volume of NaOH added is 15.62 mL, and its molarity is 0.124 M. The moles of NaOH are given by:

moles of NaOH = 15.62 mL × 0.124 M × (1 L / 1000 mL) = 0.00193648 moles.

Since moles of HF = moles of NaOH at equivalence point:

moles of HF = 0.00193648 moles.

To find the original concentration of HF, we divide the moles of HF by the initial volume of HF in liters:

Concentration of HF = moles of HF / volume of HF in L

Volume of HF = 10.0 mL = 0.010 L

Concentration of HF = 0.00193648 moles / 0.010 L = 0.193648 M

Therefore, the original concentration of the HF sample is 0.193648 M.