Chemistry help? (solution concentrations)

yikes. i'm lost. answer any or all if you can. thank you!!

1) a mixture contains 76.5% sodium chloride, 6.5% magnesium chloride, and 17% sodium sulfate by mass. what is the molarity of cl ions in solution formed by dissolving 7.50g of the mixture in enough water to form 500 mL of solution?

2) pure acetic acid has a density of 1.049 g/mL at 25 degrees C. calculate the molarity of a solution of acetic acid made by dissolving 20 mL of acetic acid at 25 degrees in enough water to make 250 mL of solution.

3) a 35.90 mL sample of 1.00 M KBr and a 60.0 mL sample of 0.600 M KBr are mixed. the solution is then heated to evaporate enough water until the total volume is 50.0 mL. what is the molarity of the KBr in the final solution?

Question 1:

Since you only care about the Cl- ions, you don't need to do the calculations for Na2SO4

Pre-step: Find the molecular weights (MW) of NaCl and MgCl2. Do so by taking the number of a specific type of atom and multiplying it by the MW as found on a periodic table. Repeat for each type of atom and add all the values together.

1(23) + 1(35.5) = 58.5 g/mol NaCl
1(24.3) + 2(35.5) = 95.3 g/mol MgCl2


Step 1. Find the number of grams of each component based on the % given. Do this by multiplying the given mass (7.50 g) by the percent in decimal form (.765 and .065 ).

7.50 g x .756 = 5.7375 g NaCl
7.50 g x .065 = 0.4875 g MgCl2

Step 2. Convert the g to moles by taking the mass and dividing it by the MW.

5.7375 g NaCl / (58.5 g/mol NaCl) = .0981 mol NaCl
0.4875 g MgCl2 / (95.3 g/mol MgCl2) = .00512 mol MgCl2

Step 3. Find the moles of Cl in each by taking the moles of the know and multiplying it by the mole ratio. The mole ratio needs a balance equation or full molecular formula. Take the number of mole of the unknown (1 and 2) and divide by the moles of the known (1 mol for both)

1/1 = 1 = mol ratio for Cl to NaCl