need help solving these 3. The molar mass and ionization constant of an unknown

ID: 1029437 • Letter: N

Question

need help solving these

3. The molar mass and ionization constant of an unknown weak monoprotic acid Concentration of standardized NaOH titrant mol/L Mass concentration of unknown weak monoprotic acid Trial 1 Trial 2 Measured pH of the unknown acid solution Mass of unnown acid solution taken for titration Initial buret reading of NaOH titrant Final buret reading of NaOH titrant Net volume of NaOH Millimoles of NaOH to end point of titration Millimoles of unknown acid in sample Molar concentration of unknown acid solution Calculated molar mass of unknown acid mL 8.mL mL mmol mmol mol/L g/mol mmol mmol mol/L Calculation of the ionization constant for an unknown acid from the measured pH samples of unknown acid you titrated, use the average values in the calculation of the Average molar concentration of unknown for the samples you titrated mol/L Average pH of the unknown acid samples. (Average the pH and molar concentration values for the ionization constant.) Cal culate the corresponding [H,0*], compute the concentration of A and HA, and cal- culate the dissociation constant, K M A M HA HA Lab Report: Determination of the Molar Mass and lonization Constant

Explanation / Answer

Measured pH of the unknown acid solution

3.0

Mass of unknown acid solution taken for titration

18.5

Initial buret reading of NaOH titrant

50.0

Final buret reading of NaOH titrant

8.5

Net Volume of NaOH

41.5

Millimoles of NaOH to end point of titration

(volume of NaOH in mL)*(molar concentration of NaOH) = (41.5 mL)*(1 M) = 41.5 mmole.

Molar concentration of unknown acid solution

(see below) 0.00538 mol/L

Calculated molar mass of unknown acid

We have 41.5 mmole unknown acid HA = 18.5 g HA. Therefore,

Therefore 1 mole HA = (18.5 g HA)/(41.5 mmole HA)*(1 mole HA)

= (18.5 g/41.5 mmole)*(1 mole HA)*(1000 mmole HA/1 mole HA) = 445.78 g.

The molar mass of the acid is thus 445.78 g/mol.

Next we calculate the molar concentration.

The mass concentration of the acid is 2.4 g/L.

Mole(s) of HA corresponding to 2.4 g = (2.4 g)*(1 mole/445.78 g) = 0.00538 mole.

Therefore, 2.4 g/L HA = 0.00538 mol/L HA.

The molar concentration of HA is therefore, 0.00538 mol/L.

I doubt you have noted down all the values correctly. Please check again.