[crystalb]

I have done this so many times.. and I can't seem to get it right. Any help would be greatly appreciated.

I have a sterile 10% solution of glucose [C6H12O6].

Calculate the volume of the 10% glucose solution that would be needed to prepare 250ml of a bacterial culture medium containing 5mM (mmol.l-1) glucose.

Express your answer in ml to 2 decimal places.

Relative Atomic Masses (Ar) or Atomic Weights
H = 1; C = 12; O =

[Borek]

Density of 10% w/w glucose is 1.0377 g/mL.

Volume times target concentration gives amount of glucose needed - in moles (or mmoles, it doesn't matter as long as you remember about it). Convert moles to grams, find out what mass of the 10% solution you need, divide by density - and you have a volume.

Or download CASC Unfortunately (for you) glucose density table is present only in the registered version,

[crystalb]

I was told that you weren't meant to use the denstiy in this calculation.. is there some other way?. Also you work out the moles (1.25E-3) and the mass (0.225g) but I am still unsure about where to go for here. Perhaps you could spell it out a bit more for me?
Cheers for your help

[AWK]

The only way is to accept an error within 5% using density ow water instead of the real density

[Borek]

I was told that you weren't meant to use the denstiy in this calculation.. is there some other way?

No. See AWK answer.

Also you work out the moles (1.25E-3) and the mass (0.225g) but I am still unsure about where to go for here.

You need 0.2252g glucose - it is 10% of the solution. So you need 0.2252/0.1 gram of solution which is 2.252g - and to convert mass to volume you need density.

Edited: It just occured to me... If the concentration given as 10% is %w/v (as opposed to %w/w) there is no need for density. But %w/v is faulty by definition, in CASC help I have described 138% w/v sulfuric acid.