· What effect would using a tap water have on the freezing point depression? How

Question

· What effect would using a tap water have on the freezing point depression? How would this affect the accuracy of the molar mass?

· Describe what is occurring during each portion of your cooling curves for Trial 1 and 2 or 3. For example, explain why the slope is zero, negative, very negative, positive, etc.

· In northern states, salt is spread out on roads to keep them from freezing. Why not use sucrose? At what temperature is it pointless to dispense salt

Explanation / Answer

tap water has MG+2, Ca+2, Na+, and plenty other ions, they will depress the point of freezing, since colligativ eproperties of water will interact with ions

If we assume there are no ions, the charges/molarity of ions will interact as follows:

dTf = -Kf*m*i

if i = not 1, then it will decrease the depression point

note htat for cations in solutoin with +1,+2,+3 charges, i > 1 for sure

then

MW will be "lower" than it acutally is

The temperature change is "zero" because, the freezing of water TAKES time, so T is constant

the slpe is negative with respet to temperature since we are FREEZING and COOLING

We use CaCl2, which has Ca+2 and 2Cl- ions

sucrose accounts only for 1 molecule, whereas CaCl2 accounts for 3 ions, therefore the depression point is much stornger for the salt

The T at which we should avoid adding salt is the max T freezing

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