Practice Questions - Week 1

Question 1

You have 4.0 mmol/L solution of albumin (molar mass = 67,000 g/mol).

Complete the following conversions of units and calculations of concentrations and volumes. Show your answer as a number (to 1 decimal place).

(a) ___________ μmoles/mL

(b) ___________ g/L

(c) ___________ % (weight/volume)

(d) ___________ volume (in mL) containing 50 μmoles

(e) ___________ mmoles in 75 mL of this solution

Answer 1

a) 4.0

b) 268.0

c) 26.8

d) 12.5

e) 0.3

Question 2

You are asked to prepare a 200 mL solution of 160 mM HCl using a stock solution of concentrated HCl with 10.25 M. What volumes of concentrated HCl and water are required to make this solution? Show your answer in numbers (up to 2 decimal places).

(a) ___________ volume of HCl stock (in mL)

(b) ___________ volume of water (in mL)

Answer 2

a) 3.12 (2dp)

b) 196.88 (2dp)

NOTE: (a) This is a dilution using a more concentrated solution.

To calculate the volume of HCl needed, we can use the equation: C1 xV1 = C2 xV2
C1 = 160 mM HCl; V1 = 200 mL; C2 = 10.25 M, we need to find V2 and have both concentrations in the same unit.

Converting C1 to M: 160 mM = 0.16 M
Solving the equation above for V2: V2 = C1xV1/C2;
V2 = 0.160 M x 200 mL / 10.25 M = 3.12 mL of HCl

(b) volume of water to prepare 200 mL of solution
total volume = 200 mL
Volume of water = 200 mL - 3.12 mL = 196.9 mL

Question 3

You need to make 1 L of 10x (ten times) stock of 1 mM NaCl. (NO decimal places are needed)

a) What would be the final concentration (mmol/L) of this 10x stock?
_____________ mM

b) How much 10x stock NaCl would you need if you are preparing 50 mL of working solution (1x NaCl)?
______________ mL

c) What is the dilution factor to get your stock back to working concentration?

Answer 3

a) 10

b) 5

c) 10

NOTES: (a) concentration is 10 x 1 mM NaCl = 10 mM NaCl

(b) C1 xV1 = C2 xV2

C1 = 1 mM; V1 = 50 mL; C2 = 10 mM, we need to calculate V2

Solving the equations above for V2: V2 = C1xV1/C2;

V2 = 1 mM x 50 mL / 10 mM = 5 mL

(c) to convert 10 mM to 1 mM, the stock should be diluted 10x; therefore, the dilution factor is 10.