[BioBell]

Hi,

I just found these forums and they look good!

I am hoping I can receive help with a biochemical maths question, as I've always had problems knowing what to do when calculations are integrated into biology etc.

I am working through past papers in preparation for summer exams and there is the following question (which is simple).

'You prepare a standard solution of glucose by accurately weighing out 10mg of glucose and dissolving it in a total volume of 50ml of solution. What is the solution's millimolar (mM) concentration? - The RMM of glucose is 180.'

Whenever I get questions like this, my brain clogs up, even though I should be able to do it easily and quickly.

I worked through and got an answer (right or wrong?) of 21.6 mM.

I wish to know if the answer is right or wrong, as the past papers don't come with any answers so I can't check myself.

If anyone can say how they work it out (why they do certain steps) I would be grateful so I can feel more confident in these types of easy calculations.

Thanks 

[Borek]

Unfortunately it is not right.

Show how you did it.

Calling it a "math question" is an abuse, it is simple and basic arithmetic 

[BioBell]

Hi,

I know it's simple, that's what frustrates me, I used to be good at things like this but now I get confused easily for some reason.

I realised the last method was wrong so I did:

moles = mass/Mr

= 0.01/180 (0.01 to convert from mg to g)

= 5.55 x 10^-5

Then concentration = moles/volume

= 5.55 x 10^-5 / 0.05 (0.05 to convert from ml to l)

concentration = 1.11 x 10^-3 mM

Is it right this time?

[rabolisk]

No. Check your units.

[BioBell]

Is the answer I gave in M rather than mM?

If so, I would just multiply by 1000 to give 1.11 mM?

[Borek]

1.11 mM looks OK.

[BioBell]

Thank you 

I'll probably ask some other very simple questions in due course