1. You have the containers in front of you. How much should you measure out to make 100 mL of a 3% aqueous solution of sucrose?

    one way: 3 grams sucrose crystals; q.a. 100 mL with water
    another way: 30 mL 10% sucrose + 70 mL water

     

  2. You have the containers in front of you. You have dissolved 20 grams of sucrose crystals in 100 mL of water and made it up to 200 mL. What percent solution have you made?

    20 grams in 200 mL = 10 grams in 100 mL
    Thus 10%

     

  3. You have taken 100 mL of a 15% sucrose solution and added it to 200 mL of water to obtain 300 mL of what percent concentration?

    CV=CV; 15% x 100 = X x 300
    X = (15 x 100)/300 = 5%

     

  4. You dissolve 3.14 grams of NaCl crystals in some water and then make it up to 100 mL by adding more water. What is the % concentration of NaCl in the water?

    3.14%

     

  5. You are titering the medication of a patient. You need to get the blood levels to 10 ng/liter of blood. You give the patient one pill and check the blood level 6 hours later and find that it has gotten to 2.5 ng/liter. How many total pills would it take to bring the patient's titer up to the desired level?

    1 pill is to 2.5 ng as X pills are to 10 ng
    (1/2.5) = (X/10)
    X = 4 pills

     

  6. Average seawater has a salt concentration of 33 parts per thousand (33 ppt). What is the concentration in terms of percent?

    33 is to 1,000 as X is to 100
    33/1000 = X/100; X = 100 x (33/1000) = 3.3%

     

  7. This question can substitute for any TWO of the above! As you know, water has a molecular weight of 18 (16+1+1).

    1. What is the percent concentration of pure water?

      Take 100 grams of water (100 mL) and make it up to 100 mL (add nothing more!)
      Thus it is 100%.
      Even a 4th grader can tell you that pure water is 100% water!

       

    2. What is the molar concentration of pure water?

    A liter of water weighs 1,000 grams.
    moles = mass/molecular weight
    moles = 1000 grams/18 grams per mole
    moles = 55.555555

    molar = moles per liter
    there are 55.55555 moles in that liter, thus 55.5555 molar!