Difficult chemistry questions?

Question

I don't need answers to anything, just need to know what equations to use.

1a. Calculate the freezing point of a solution containing 70 g. of methanol, and 180 g. of water.

1b. Calculate the boiling point of the same solution.

2. At what temp. will a 3.00 molal solution of sodium fluoride freeze?

3. You need 500 mL of a 0.35M NaOH, how much 5.0M NaOH stock solution will you need to prepare it?

4. How many grams of salt would you need to prepare 5 L of a 2.50% NaCl solution?

5. Calculate the boiling temperature for a solution containing 1.5 mols of NaL dissolved in 1.25 kg of water.

6. Calculate the freezing point of a solution composed of 23.4 g of CaF2 dissolved in 175 g of water.

7.Calculate the malality of an aqueous solution of KBr. the boiling point of which is 108.5 degrees C.

8. How many grams of BaBR2 are in 750 mL of a 17.5% BaBR2 solution?

9.42.5 g of CaCl2 in 500 mL of a solution. Dilute to 0.25M. How much of the .25M solution could be made?

Like I said, I don't need the answers to the questions. Just the equations to use.

Answer 1

1 and 2: These are colligative property questions:
The applicable equation is:
Depression of freeze point or increase in boiling pt= Kf or Kbp * Molality.
molality = moles of solute/kg of water for non-ionic solute or g-mole of ions/kg of water.

3: Volume * Normality of diluted solution =
Volume * normality of stock solution

4. Volume of NaCl * Percentage of NaCl = wt NaCl

5. Same as 1 or 2.
6. ditto
7. Same as 1 or 2 except you know the change in boiling point and solve for molality.

8. Same as 4. The compound is BaBr2.
9. Divide 42.5 g CaCl2 by its mol wt to find molarity. Then use equation 3.

Answer 2

The freezing point depression is given by-

delta T (freezing point depression) = Kf x molality (where Kf is the constant for the solvent). Kf for water is 1.86

The boiling point elevation is given by-

delta T (bp elevation) = Kb x molality (Kb for water0.51)

The tricky part is that the bp elevation and the freezing point depression are based on the number of species in solution. If you dissolve 1.0 mole of NaCl in 1000 grams of water, you have 2 moles of species in the water: 1 mole of Na+ and 1 mole of Cl-.

Answer 3

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