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Topic: help with homework (pathetic..)  (Read 3739 times)

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diamorph

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help with homework (pathetic..)
« on: November 09, 2008, 09:34:42 PM »
a) Prepare 500mL stock solution that has a concentration of 400ppm NO3- form KNO3. How many g of KNO3 dose you need to weigh out.

b) Make a 100ppm NO3- working stock solution, form the stock solution, and name it A. How are you planning to make the A and how much are you going to make (how much are you going to use later).

c) Make a dilution series from A, make 250mL of each of the dilutions a-e
How many mL of A is needed for each dilution?

Dilution   a   b   c   d   e   f
ppm NO3-   0    2.0   4.0   8.0   12   16
mL A

i can probably, maybe work out the rest as long as i figure out a)...

enahs

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Re: help with homework (pathetic..)
« Reply #1 on: November 09, 2008, 10:00:22 PM »
ppm = mass substance * 106
mass solvent

So, you tell me how much you need.

diamorph

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Re: help with homework (pathetic..)
« Reply #2 on: November 09, 2008, 10:13:12 PM »
sorry, got a little distracted, that wasn't what i meant to post, it's this one:

The content of Manganese in a steel sample should be determined by spectroscopy. Mn is oxidized to permangante.
1.   A stock solution (stock I) that should be 1000mg Mn per Liter is prepared. How much KMnO4 do you have to weight out for 500ml of stock I solution?
2.   By dilution a stock II solution containing 100mg Mn/L is prepared. How much of stock I do you have to pipette in order to make 250ml of stock II solution?
3.   The calibration curve has to be from 0 to 20 mg Mn/L. How many ml of stock II do you need for 100ml of the following standard solutions?

Std. No.   1   2   3   4
Mg/L   2,00   5,00   10,0   20,0

i dont get the first part.
its a simple calculation, i know, i just dont understand the steel, Mn to MnO oxidation, etc thing.

Borek

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Re: help with homework (pathetic..)
« Reply #3 on: November 10, 2008, 03:27:49 AM »
its a simple calculation, i know, i just dont understand the steel, Mn to MnO oxidation, etc thing.

So start assuming there is not first statement, imagine question starts with

1.   A stock solution (stock I) that should be 1000mg Mn per Liter is prepared. How much KMnO4 do you have to weight out for 500ml of stock I solution?
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