If I add 4 g of starch into 400 mL of water, and on a separate flask, I have 4 g of microbe in 40 mL of medium, should I be reporting that:
a) 40 mL of 10 %w/v of microbe was added into 400 mL of 1 %w/v starch suspension
OR
b) Should I be calculating the true concentration, i.e. 4 g/(400+40) mL of starch, and 4g/(400+40) mL of microbes?
If I am using (a), then should I be mentioning that the starch concentration used is 1 %w/v even though it is not exactly that? And when plotting graphs for different concentrations, should I also be writing this concentration? Or I should show the true concentration after adding everything up?
I think you should mention which are your standard or stock solution ( i.e 10 %w/v of microbe and 1 %w/v starch ) and then mention wich are your final solution (i.e you final concentration or your work solution). In the case of the graphs you must use the true concentration of the work solution. I hope this help you.
Regards
In 1960, almost the whole world has signed a treaty to use SI-units whenever possible. I propose to use the true concentration instead of units which only a limited number of readers understand.
But when you mixed two solutions with known concentration, how sure are you that the final volume is the addition of both? The volume may expand or decrease. If that's the case how would you go about calculating the final concentration?
Plotting graphs for different concentrations mean that different aliquots of 4 g of microbe in 40 mL of medium are added at the constant 400 ml starch solution?
Is ally necessary to report thr concentrations as true i.e. g/l?
Are possible i.e. plots as 400 ml+1 ml, 400ml+2 ml...?
Excuse!
Plotting graphs for different concentrations mean that different aliquots of 4 g of microbe in 40 mL of medium are added at the constant 400 ml starch solution?
Is really necessary to report the concentrations as true i.e. g/l?
Are possible i.e. plots as 400 ml+1 ml, 400ml+2 ml...?
I am puzzled by the recommendation of the use of SI units because the molecular weight of the starch and the microbe are unknown. As long as the experimenter describes exacly how the suspensions are made, other experimenters can repeat the procedure exacly should they wish to do so. It is also helpful however, if brief deatils are given of the mpurity of the starch, i.e. contents of water, protein, lipid and ash should be included.
Peter Butterworth
King's Coillege London
I agree with Peter on this. You should leave it as you had described it "as add 4 g of starch into 400 mL of water, and on a separate flask" and then "place 4 g of microbe in 40 mL of medium". If you combined these two solutions/suspensions into a single container, then say so. You do not have to use descriptions in % because that would require for you to calculate using the percentage purity of the starch and the microbe which would make this "40 mL of 10 %w/v of microbe was added into 400 mL of 1 %w/v starch suspension" incorrect because this simply used the mass of each components as if these were 100% pure. However, if you are sure they are 100% pure, then say so in your description.
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