Posted by alex on Wednesday, May 12, 2010 at 12:38pm.
I would set up a proportion.
315ppm/6.7 = xppm/10
and solve for x.
that proportion solving for X doesnt give me a number listed as an option..I got 470
I never liked the drops way of doing things. Having said that, I must take the blame and say I made a mistake.
If it takes 3 drops of the EDTA for the known of 315 ppm and it takes only 2 drops for the unknown, the unknown must be weaker. You can do it by drops of EDTA (which makes more sense to me)
315 x 2/3 = ??
or you can use the ratio set up to give a smaller number; i.e.,
315 x (6.7/10) = ?? ( you don't get the same number because the 6.7 was rounded off from 6.66667 to 6.7).
or you can set up a ratio/proportion but the reverse of what I have above.
I suppose it's obvious but I didn't even look at the options for answers; perhaps I should have looked.
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