Question

9 mg of glucose is dissolved in 5 ml of water. the molecular weight of glucose in 180 g/mol. what is the concentration of glucose in units of micromolars?

Answer 1

Solution:- Mass of glucose = 9 X 10^-3 g and mass of water = 5 ml X 1 g/ml = 5 g.

[ because the density of water = 1 g/ml]

Moles of glucose in 5g of water = (9 X 10^-3) g / (180 g/mol) [ 1 mg = 1 X 10^-3 g]

= 0.05 X 10^-3 = 0.00005 Mole

Molality = 0.00005 Moles / (5 X 10^-3 Kg)

= 0.01 Moles/Kg.

Now, to find out the molarity, we need to find out the solution's volume. In order to get the solution's volume, we need to find out the solution's density by the percent concentration by mass of the solution:

% w/w = {0.009 g / (5 + 0.009) g} X 100 = 0.18%

At this % w/w, the density of the solution is around same as that of the water, i.e. 1 g/ml.

Volume of the solution = Total mass / Density of solution = 5.009 g / 1 g/ml

= 5.009 X 10^-3 Litres

Thus, Molarity of glucose = 0.00005 moles / (5.009 X 10^-3 L)

= 0.0099 moles/L = 0.01 M (approx)

Concentration of glucose in Micromolars = 10000 MicroM