Question

A student sets up a titration with a * 1 point buret filled with 0.5 M NaOH. In the flask below they place the phenolphthalein indicator and 6.2 mL of the unknown acid. The solution in the beaker turns pink after exactly 24.8 mL of NaOH have been added. Find the exact concentration of the unknown acid.

Answer 1

2.00 M

Step-by-step explanation:

In a titration, we can determine the concentration of an unknown acid by adding a known concentration of a base, such as NaOH, until the reaction is complete. At the endpoint of the reaction, the amount of base added is equal to the amount of acid present in the sample.

From the problem, we know that the NaOH solution has a concentration of 0.5 M, and that 24.8 mL of NaOH is required to completely react with the unknown acid in the flask. We can use this information to calculate the number of moles of NaOH that were added:

moles of NaOH = concentration x volume

moles of NaOH = 0.5 mol/L x 0.0248 L

moles of NaOH = 0.0124 moles

Since the reaction is a neutralization reaction between an acid and a base, the number of moles of NaOH added is equal to the number of moles of acid in the flask. Therefore, we can calculate the concentration of the acid using the volume of acid added:

moles of acid = moles of NaOH

moles of acid = 0.0124 moles

volume of acid = 6.2 mL = 0.0062 L

concentration of acid = moles of acid / volume of acid

concentration of acid = 0.0124 moles / 0.0062 L

concentration of acid = 2.00 M

Therefore, the exact concentration of the unknown acid is 2.00 M.