1. You need a 0.5% solution of sodium thiosulfate. How much do you weigh out ot make 100 mL of such a solution?

    0.5 grams

  2. You need to make 200 mL of a 0.2% solution of aluminum potassium sulfate. How much do you weigh out to make up to 200 mL?

    0.4 grams

  3. From the containers in front of you, how much of which do you measure out to make 100 mL of 2% lactose?

    You were provided only with 4% lactose and 5% lactose.
    Easier way: dilute the 4% in half: 50 mL of 4% + 50 mL of water.
    Harder way - use the 5%: CV=CV; 5%xV=2%x100 mL; V = 40 mL of 5%.

  4. You need 100 mL of 25% sucrose, and have weighed out 25 grams of crystaling sucrose. How much water do you use?

    Dissolve the 25 grams into about 70 mL of water, and then add enough water to make the volume 100 mL.

  5. You have added 24.8 grams of sodium chloride to 100 mL of water, and swirled it until it all dissolved. You then added enough water to make it up to 200 mL. What % solution did you make up?

    24.8 grams in 200 mL = 12.4 grams in 100 mL; 12.4%

  6. You need 1 liter of 1 molar NaCl. How much NaCl do you weigh out to make this?

    58.44 grams

  7. (This may substitute for any two previous questions above.)
    1. Which solution has the higher % concentration: 1 M NaCl or 1 M ZnCl2
    2. What is the % concentration of 1 M NaCl?

    ZnCl2, because you had to weigh out more of it than of NaCl
    1 M NaCl = 58.44 grams/1000 mL = 5.844/100 mL; thus 5.844%.