# 8. Determine the mass of NaCl necessary to lower freezing point of ...

## Question

8. Determine the mass of NaCl necessary to lower freezing point of 300 mL of distilled water to -10°C:
Mass NaCl needed:
9. Based on the actual mass of NaCl you used (#1), determine the theoretical freezing point of the ice/ saltwater bath:
Theoretical freezing point:
10. Determine the % error for the temperature of your ice/saltwater bath (comparing the temperature you measured, #2, and the theoretical freezing point, #9):
(temperature) measured - (temperature) theoretical
% error = ------------------------------------------------------------------------ X 100 Equation 14
(temperature) theoretical
% Error:
II. Molar mass determination of ethylene glycol: cooling curve for pure water
11. Plot cooling curve (temperature VS. time) for water (data in #4):

12. Use a straightedge the data (e.g., a ruler) to draw two straight lines on each cooling curve-one drawn make through the region points after before the the water freezes, and one drawn through the data points that to the y-axis).
The intersection of these two lines is the freezing point (determine by extrapolating this point up water begins freezing (e.g., the region where the curve plateaus).
Freezing point of water:
Trial 1:
Trial 2:
Average:

13. Determine the % error for the freezing point of water (comparing the average temperature you determined in #12 and the actual freezing point; NOTE: use Kelvin):
% Error:
III. Molar mass determination of ethylene glycol: cooling curve for aqueous ethylene glycol solution

14. Mass of water:
Trial 1:
Trial 2:

15. Molality of aqueous ethylene glycol solution:
Trial 1:
Trial 2:

16. Plot cooling curve (temperature vs. time) for water (data in #7):

19. The actual molar mass of ethylene glycol is 62.07 g mol-1. Calculate the % error for your average molar mass:
% Error:

Reflection Questions
1. Provide possible reasons for the % error in the temperature of your ice/saltwater bath (#10, Analysis section):

3. Provide possible experimental errors to explain the % error in your Ti of water (#13):

5. Provide possible experimental errors to explain the % error in your calculated molar mass of ethylene glycol (#19):

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