Science Buddies: "Ask an Expert"

I'm doing the experiment "Chemistry of ice-cream making: Lowering the freezing point of Water." I have to do all these math equations to find out the freezing point depression and all this stuff but I've never learned how to do it. I'm so confused and I have to use my data and put it in the equations ΔT = Kf m i and Tn = Tf - ΔT and I don’t know what that means and I need help so badly please help!!!!! My whole report and everything is due on January 4th, 2013!! Help please!!! And it’s talking about molality and the explanations for this don’t make sense to me please help ASAP ! In the description it said this was for 9+ graders I'm in 8th.

Hello sn101,

As you say, the project was recommended for 9+ grades, so it's no wonder that you have to do some extra learning. The equations are simple algebra. I'll provide some help, but if you still don't understand, you will need to find someone who understands algebra to explain further.

ΔT = Kf m i

This equation says that the freezing-point depression can be calculated by multiplying the molal feezing-point-depression constant times the molality of the solution times the van't Hoff factor of the solute. That's a long sentence, so the equation is written using symbols. Instead of " molal feezing-point-depression constant" the equation uses the symbol "Kf." Please read, study, and think about Equation 2 in the Background section of the Project Description. Each number you need to know has its symbol. If you collect those numbers for your experiment and multiply them, you get your answer, ΔT.

Follow the same substitution of numbers for symbols in Equation 3, and you have answered your question about the equations.

Molality is defined by Equation 1. It says simply that molality is the amount of solute dissolved in an amount of liquid. What is the solute and solvent in this experiment? How much of each did you use?

Good luck, WW

I am working on the same project as sn101, and I understand most things, but molality. Could you give me an example of a sucrose solution's molality. If I can understand molality, it will help me clarify the rest of my projects. HELP please!!!

Hello,
I figured out molality! It was just simply dividing the solute (salt or sugar) by the solvent (the water), then dividing that answer by the molecular weight!!!

Yours truly,

Threepointhoopster25