Calculation problem

[35%Daffodil]

Hi,

I've been doing the calculations in the Introduction to Pharmaceutical Calculations book, but I have become really stuck on one problem.

pg. 87, question 5:

What weight of malachite green oxalate is required to produce 300ml of a solution such that 25ml of this solution diluted to 2000L gives a 0.5ppm solution?


Basically I've worked out:

0.5g = 1g
1000000ml 2000L

therefore in 25ml there is 1g.

1g = x
25ml 300ml

x = 12g

But the answer in the book says 12mg so I'm really stuck!!

Any help would be greatly appreciated.

Thanks

[DavidS]

What weight of malachite green oxalate is required to produce 300ml of a solution such that 25ml of this solution diluted to 2000L gives a 0.5ppm solution?

But the answer in the book says 12mg so I'm really stuck!!

I'm afraid I get 12G as well. Who can help us out?

[paul2008]

I think

2000ml of a 0.5ppm (0.5g/1 000 000ml) contains 1mg
[ working x/2000=0.5/1 000 000 so x=1/1000)

and then the answer works out as 12mg.

[35%Daffodil]

Its 2000Litres not 2000ml.

[paul2008]

Its 2000Litres not 2000ml.

ok, I missed that... probably a typo somewhere.

[DavidS]

ok, I missed that... probably a typo somewhere.

Well, I wondered about that too.

I looked on the pharmpress website to see if there is an errata published, but couldn't find one.

Who is going to email the publisher and find out ..........

[Nik]

The answer in the book is wrong - I also worked it out to 12g. If you look at example 4.11 (p77) the question is very similar but they've tweaked a few values and the answer they give is 20g for that particular question. So don't worry you are right.

[Nik]

I looked on the pharmpress website to see if there is an errata published, but couldn't find one.

Might be mentioned in the second edition.

[bobbin]

Might be mentioned in the second edition.

Oh, I got 12mg.

[Nik]

Could you show us your working out bobbin ?