I need help with these questions and calculations Use the following questions to

Question

I need help with these questions and calculations

Use the following questions to assist in determining the molecular mass of the unknown. Be sure to show all calculations. Include the proper significant figures and units! Determine the deltaT_f for the two trials performed. Using the K_f for acetic acid, determine the molality of the solutions for the two trials performed using the equation for freezing point depression in the introduction. Covert the mass of acetic acid from g to kg for each trial. Use the mass of acetic acid in each solution and the molality of the solution calculated in #2 to determine the number of mol of unknown present in each solution. Determine the molecular weight of the unknown using the mass weighed out for each trial. Calculate the average molecular weight of the unknown based on the two trials.

Explanation / Answer

1) dTf = T0 - Ts

Trial 1 : dTf = 14.1 - 11.3 = 2.8

Trail 2 : dTf = 14.2 - 11.4 = 2.8

2) dTf = Kf * m

Trail 1 : m = 2.8 / 3.9 = 0.718

Trail 2 : m = 2.8 / 3.9 = 0.718

3) mass of acetic acid

Trail 1 : 21.03 g = 21.03 / 1000 kg = 0.02103 kg

Trail2 : 21.328 g = 21.328 / 1000 kg = 0.02133 kg

4) number of moles of acetic acid

Trail 1 : 21.03 / 60 = 0.3505

Trail 2 : 21.328 / 60 = 0.3554

5) Molar mass of un known M = Kf * m / dTf

Trail 1 : M = 3.9 * (1.337 / 2.8) *(1000 / 21.03) = 88.55 g/mol

Trail 2 : M = 3.9 * (1.336 / 2.8) *(1000 / 21.0328) = 88.47 g/mol

6) Average molecular weight = (88.55 + 88.47) / 2 = 88.51 g/mol

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---