From a 10 ml sample a 1 ml aliquot was taken and diluted to...

From a 10-mL sample, a 1-mL aliquot was taken and diluted to 100 mL. From this, a 5-mL aliquot was taken and diluted to 20 mL. The final 20 mL was found to have a concentration of 0.004 M analyte X. What is the concentration of analyte X in the 10-mL sample? a. 16 M b. 1.6 M c. 0.016 M d. 0.004 M e. 0.001 M f. 0.00001 M

Transcript

0:00 All right.

00:01 This question is asking about a series of dilution steps that you perform in a lab to run a sample.

00:07 And so it tells us we have a 10 -millimeter sample.

00:10 We take one millimeter from that and diluted it down to 100 millimeters.

00:13 We then take 5 milliliters from that and dilated it to 20 millimeters.

00:17 We find that the concentration of x or the analyte we're concerned about is 0 .004 molar.

00:22 And wants to know what the concentration is in the original sample.

00:26 And so this question is a simple problem worded in a very confusing way.

00:33 And so i'm going to draw quite crudely what exactly is going on here.

00:41 And that might make a little easier to follow along.

00:48 So we have original sample here.

00:51 We have a 10 -millimeter sample.

00:54 We take one millimeter from that and then we throw in 99 milliliters of water or we do it so the total volume is that hundred millimeters dimensions.

01:08 So this is one step, also called step one, or dilution one.

01:13 This is the first dilution.

01:15 We then take five millimeters in that and toss in 15 melalaters of water to a total volume of 20 millimeters.

01:29 So this is what we actually performed in the lab.

01:31 And this could be step two.

01:32 So it makes it seem like there's like five steps in the way the question of word did, but this is actually only two dilutions going on.

01:39 We're going from a 10 milliliter sample down to this first dilution and then diluting it one more time.

01:46 So there's actually only two dilutions.

01:53 We have first dilution and second dilution to worry about.

02:03 So if we follow the dilutions, that's all we need, right? because this one millimeter sample is the same concentration as this 10 millimeter sample.

02:10 This 5 millimeter sample is the same concentration from the 100 -millimeter.

02:15 Dilution step...

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