A 0.2500 M NaOH solution was used to titrate a 16.85 mL hydrofluoric acid solution. The endpoint was reached after 31.20mL of titrant were added. Find the molar concentration of hydrofluoric acid in the original solution.

To find the molar concentration of hydrofluoric acid (HF) in the original solution, we can use the concept of stoichiometry and the balanced chemical equation for the reaction between NaOH and HF.

The balanced chemical equation for the reaction is:

NaOH (aq) + HF (aq) → NaF (aq) + H2O (l)

From the equation, we can see that 1 mole of NaOH reacts with 1 mole of HF, so the mole ratio is 1:1.

Given:
Molarity of NaOH solution (M1) = 0.2500 M
Volume of NaOH solution (V1) = 31.20 mL = 0.03120 L
Volume of hydrofluoric acid solution (V2) = 16.85 mL = 0.01685 L

First, we need to calculate the number of moles of NaOH used in the reaction. We can use the formula:

moles = molarity × volume (in liters)

moles of NaOH (n1) = M1 × V1
= 0.2500 M × 0.03120 L

Next, we know that the mole ratio between NaOH and HF is 1:1. Therefore, the number of moles of HF (n2) is also equal to n1.

moles of HF (n2) = moles of NaOH (n1)

Now, we can calculate the molar concentration of HF in the original solution using the formula:

molarity = moles / volume (in liters)

Molarity of HF (M2) = n2 / V2

Substituting the values:

Molarity of HF (M2) = n1 / V2

Molarity of HF (M2) = (0.2500 M × 0.03120 L) / 0.01685 L

Finally, calculate the molar concentration of HF:

Molarity of HF (M2) = 0.462 M

Therefore, the molar concentration of hydrofluoric acid in the original solution is 0.462 M.

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