1. You have a bottle of NaCl (f.w. 58) in front of you. How much should you weigh out to make 100 mL of a 1% aqueous solution?

    "1%" means 1 gm/100 mL.
    Thus 1 gram!

     

  2. You have a bottle of NaCl (f.w. 58) in front of you. How much should you weigh out to make 1.0 liter that is 1.0 M?

    "1M" means the formula weight in grams per liter
    Thus 58 grams of NaCl made up to a liter with water.

     

  3. You have a flask of 2% NaCl (f.w. 58) in front of you. How much of it should you use to make 100 mL that is 1%?

    You need to dilute it in half.
    One way: Take 50 mL of 2% and add 50 mL of water → 100 mL of 1%

    Another way: CV = CV; 2% x V = 1% x 100 mL; V = ½ x 100 mL = 50 mL

     

  4. You have a bottle of NaCl (f.w. 58) in front of you. How much should you weigh out to make 200 mL that is 1.5%?

    100 mL of 1.5% would require 1.5 grams of NaCl;
    Thus 200 mL would require 2 x 1.5 = 3 grams

     

  5. You have a bottle of NaCl (f.w. 58) in front of you. How much should you weigh out to make a liter that is 0.5 M?

    This is like question 2 but only half as concentrated.
    Thus add only half as much (29 grams) and make it up to a liter with water.

     

  6. You have a flask of 10% sucrose (mol.wt. 348) in front of you. How much should you use to make 100 mL that is 1%?

    CV = CV;
    10% x V = 1% x 100 mL;
    V = (1/10) x 100 = 10 mL

     

  7. You have the bottle in front of you, which contains powdered MacConkey agar. You want to test whether your strain of E.coli is capable of using the sugar lactose. If the colonies that grow up are red, it uses lactose, but if they grow up light pink, they do not use lactose. How much of the MacConkey powder do you add to water to make 100 mL that 1%?

    See #1: 1 gram

    How much to make 300 mL that is 0.5%?

    For three-times as much; add 3 grams!

     

  8. You are making stabs (or "deeps") for long-term storage of your cultures. While ordinary nutrient agar works fairly well, it would be better to use a nutrient agar that has only 1% agar - a bit slushy. So you find a bottle of nutrient broth, and make up 300 mL as per its label. How much pure agar powder do you weigh out to make that 300 mL to 1% in agar?

    Just like the previous question: 3 grams.

     

  9. You are microscopically comparing the erythrocytes of yourself with those from a person with sickle-cell anemia. You find your stock of normal saline (aka physiological saline) is depleted. How much NaCl do you add to 1000 mL of water to make it 0.9%?

    0.9% means 0.9 grams in 100 mL
    But a liter is 10-times as much: thus 10 x 0.9 = 9 grams.