Question

A) You need to make 250ml of a 20x stock solution of NaCl to dilute later to a final concentration of 50 mM. The M.W. of NaCl is 58.44. How would you accomplish this?

      NaCl ___________ g

      Pure Water __________ ml

B) You need 3.5 L of 50 mM NaCl from your 20x stock. How would you accomplish this?

     20x stock ______ ml

     Pure water ________ ml

C) You need to make 20 ml of a 20% glucose solution. The M.W. of glucose is 180.16. How would you accomplish this?

     Glucose ________ g

    Pure water _______ ml

Answer 1

A)
concentration of NaCl solution = 20*50 mM
= 1000 mM
= 1 M
volume = 250 mL
number of moles of NaCl = M * V
= 1 M * 0.250 L
= 0.250 mol
molar mass of NaCl = 58.44 g/mol
mass of NaCl = 58.44 g/mol * 0.250 mol
= 14.61 g
Answer:
14.61 g
250 mL

B)
use:
Ms*Vs = Mf*Vf
1000 mM * Vs = 50 mM * 3.5 L
Vs = 0.175 L

20x solution = 175 mL
pure water = total volume - volume of 20x solution
= 3500 - 175
= 3325 mL

C)
since density of solution is 1g/mL,
mass of solution = 20 g
mass of glucose = 20% of 20 g = 4 g
mass of water = 16 g

Answer:
glucose = 4 g
water = 16 mL