Module 2. Test A: Amount and Concentration.
1
You have only 0.5 mg of a purified enzyme sample in a bottle. You need to make a 0.2 % w/v solution, what volume of water would you need to add?
volume = ml
2
(a) Vodka has an ethanol concentration of 20 % w/v. If one was to drink 25 ml of straight undiluted vodka, what amount of alcohol would be consumed (in grams)?
(b) The relative molecular mass of ethanol is 46. How many moles of ethanol would one have consumed? (to two significant figures)
(c) If this amount of ethanol was dissolved in all of the blood volume (unlikely, but this is just for fun) which in this individual was 5 L, what would the concentration of ethanol be in the blood (in mol/L)?
(a) amount of ethanol consumed = g; (b) amount in moles = mol (two significant figures); (c) concentration in blood = M (two significant figures)
3
300 ml milk contains 1.2 μg vitamin B12 (relative molecular mass is 1355). What is the concentration of vitamin B12 in millk to two significant figures in M with an appropriate prefix?
M (number)..... (prefix)
4
The daily recommended intake of vitamin C is 25 mg for a 4 year old boy and most commercially available orange juice contains approximately 0.5 mg/ml. How much orange juice would a 4-year old boy need to drink to get his daily allowance?
amount of juice = ml
5
The relative molecular mass of vitamin C is 176.
The concentration of vitamin C in orange juice is 0.5 mg/ml, this could be written as mM (two significant figures). The amount of vitamin C in a cup of 250 ml is mmol (two significant figures)
6
Peptide hormones activate cells by binding to receptors at the cell surface. In an experiment you have shown that in a sample of 1 million cells there are approximately 0.02 pmol of receptors. How many receptor molecules does this correspond to?
Number of molecules per cell =
7
If you mix 100 ml orange juice (containing 0.5 mg/ml vitamin C) with 50 ml vodka (containing 20% w/v ethanol) what would the resulting concentrations of vitamin C and ethanol be?
concentration of vitamin C = mg/ml (two significant figures); concentration of ethanol = mg/ml (two significant figures)
8
If you take 8 ml of a stock solution of an antibiotic such as ampicillin at a concentration of 25 mg/ml then dilute this 1:200, what would the resulting concentration and volume be?
concentration = mg/ml (two significant figures); volume = L (two significant figures)
9
A 2 ml sample of blood cells was diluted 1:5 before measuring the cell concentration in a haemocytometer. When measuring the cell count in the haemocytometer, 200 cells were counted in a volume of 10 uL. How many cells were contained in the original 5 ml sample?
2 ml of the original sample contained cells
10
What volume of a 0.5 M KCl solution must be added to 1 ml of an enzyme solution to bring the enzyme solution to a KCl concentration of 0.5 mM?
Volume of 1 M KCl = mL
