ASA is the pain reliever in aspirin. ASA is a weak acid with [tex]K_a = 3.2 \times 10^{-4}[/tex]. One aspirin tablet was ground up and dissolved in 25.0 mL of water. It was titrated using 0.15 mol/L sodium hydroxide. To reach the endpoint, 98.3 mL of base was required.

Determine the concentration of the ASA solution.

To find the concentration of the ASA solution, you calculate the moles of NaOH used during titration, equate it to the moles of ASA, and then divide by the volume of the ASA solution to get the molarity. For the given values, the concentration of the ASA solution is 0.5898 mol/L.

Explanation:

To determine the concentration of the ASA (acetylsalicylic acid) solution, we need to perform a titration calculation. Since ASA is a weak acid, it will react with the strong base sodium hydroxide (NaOH) to produce water and the corresponding sodium salt of ASA. The equation for the reaction is:

ASA (aq) + NaOH (aq) → NaAspirinate (aq) + H2O (l)

The titration process involves adding a known concentration of the base to the acid until the reaction reaches the endpoint, where the amount of base added is stoichiometrically equivalent to the amount of acid initially present.

To calculate the concentration of the ASA solution, we can use the following steps:

Calculate the moles of NaOH used using its concentration and the volume added at the endpoint.
Since the molar ratio of ASA to NaOH in the reaction is 1:1, the moles of NaOH will be equal to the moles of ASA.
Use the volume of the ASA solution to calculate its concentration in mol/L (molarity).

Example calculation:

Volume of NaOH titrant used = 98.3 mL = 0.0983 L

Concentration of NaOH titrant = 0.15 mol/L

Moles of NaOH = Volume × Concentration = 0.0983 L × 0.15 mol/L = 0.014745 mol

Moles of ASA = Moles of NaOH = 0.014745 mol

Volume of ASA solution = 25.0 mL = 0.025 L

Concentration of ASA solution = Moles of ASA / Volume of ASA solution

= 0.014745 mol / 0.025 L = 0.5898 mol/L