# Chemical Forums

## Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Tyyyyuuu on September 28, 2020, 01:33:36 PM

Title: Dispute on the accuracy of this serial dilution
Post by: Tyyyyuuu on September 28, 2020, 01:33:36 PM
I think the last dilution in this series is 1 in 5 not, as it indicates in the table, 1 in 10. Am I wrong?!?! (the unit of volume is arbitrary, but lets say mL)
Title: Re: Dispute on the accuracy of this serial dilution
Post by: Borek on September 28, 2020, 04:32:58 PM
That would mean all earlier dilutions are wrong as well, wouldn't it?
Title: Re: Dispute on the accuracy of this serial dilution
Post by: Tyyyyuuu on September 28, 2020, 05:17:25 PM
That would mean all earlier dilutions are wrong as well, wouldn't it?

Thank you for your input. I suppose the "analytical dilution" makes sense if it's intended to be relative to just the prior dilution, and not the original stock solution. But if that's the case then the last dilution is 1 in 5 relative to the penultimate dilution.  ???
Title: Re: Dispute on the accuracy of this serial dilution
Post by: Borek on September 28, 2020, 05:42:02 PM
No, I think you are misunderstanding something here. These dilutions are cumulative, each next one uses the previous solution.

But if that's the case then the last dilution is 1 in 5 relative to the penultimate dilution.

No, it is 1.25 (240/192).
Title: Re: Dispute on the accuracy of this serial dilution
Post by: Tyyyyuuu on September 28, 2020, 06:28:09 PM
No, I think you are misunderstanding something here. These dilutions are cumulative, each next one uses the previous solution.

But if that's the case then the last dilution is 1 in 5 relative to the penultimate dilution.

No, it is 1.25 (240/192).

I follow what you are saying, but this is my line of thinking:

From the first row in the table, to the last:

450 mL diluent + 450 mL analyte is a 1 in 2 dilution
320                 + 640                        1 in 3
240                 + 720                        1 in 4
180                 + 720                        1 in 5
130                 + 650                        1 in 6
090                 + 540                        1 in 7
055                 + 385                        1 in 8

048                 + 640                        1 in 5 (not 1 in 10)
Title: Re: Dispute on the accuracy of this serial dilution
Post by: Borek on September 28, 2020, 06:53:42 PM
048                 + 640                        1 in 5 (not 1 in 10)

Why 640 and not 192? You have changed the rules for this one line.
Title: Re: Dispute on the accuracy of this serial dilution
Post by: Tyyyyuuu on September 28, 2020, 07:04:08 PM
048                 + 640                        1 in 5 (not 1 in 10)

Why 640 and not 192? You have changed the rules for this one line.

You're right, sorry, that was an error, (but the conclusion is the same)

450 mL diluent + 450 mL analyte is a 1 in 2 dilution
320                 + 640                        1 in 3
240                 + 720                        1 in 4
180                 + 720                        1 in 5
130                 + 650                        1 in 6
090                 + 540                        1 in 7
055                 + 385                        1 in 8

048                 + 192                        1 in 5 (not 1 in 10)
Title: Re: Dispute on the accuracy of this serial dilution
Post by: Borek on September 29, 2020, 02:59:37 AM
Your results are inconsistent. Show how you got 1 in 5 in the last line and explain how you got correct results for all previous lines.
Title: Re: Dispute on the accuracy of this serial dilution
Post by: Tyyyyuuu on September 29, 2020, 03:07:04 AM
Your results are inconsistent. Show how you got 1 in 5 in the last line and explain how you got correct results for all previous lines.

Is 1 mL A plus 1 mL of water not a 1 in 2 dilution of A? That is, one unit of A in a total of 2 units of solution.
Title: Re: Dispute on the accuracy of this serial dilution
Post by: Borek on September 29, 2020, 03:12:30 AM
It is, but what about the next one?

Perhaps you are missing the fact that each next step uses not the original stock solution, but solution from the previous step? That's what 'serial' means.