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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: Hielly on November 15, 2009, 02:12:30 pm

Title: ppm
Post by: Hielly on November 15, 2009, 02:12:30 pm

a sample of pond water contained 88.00 microgram g-1 of dissolved oxygen gas. calculate the amount in grams of dissolved oxygen in 4.00L of pond water.


thanks

answer says 0.352g

Title: Re: ppm
Post by: fady_22 on November 15, 2009, 02:25:47 pm

As the density of water is equal to 1, the mass of water= volume of water. So, 4 L of water= 4000 g.
m(02)= 88*10^-6 g/g water *4000 (as 1 microgram= 10^-6 g)
        =0.352 g

Title: Re: ppm
Post by: Hielly on November 15, 2009, 02:33:09 pm

Quote from: fady_22 on November 15, 2009, 02:25:47 pm

As the density of water is equal to 1, the mass of water= volume of water. So, 4 L of water= 4000 g.
m(02)= 88*10^-6 g/g water *4000 (as 1 microgram= 10^-6 g)
        =0.352 g

thanks i got the mass of water and solute, which is what you got. Then i subbed it in the c=mass/volume

would you say the concentration is 4000 ? from water. i got confused here

Title: Re: ppm
Post by: samuch on November 15, 2009, 02:43:42 pm

how did you get 4000?

Title: Re: ppm
Post by: d0minicz on November 15, 2009, 02:47:46 pm

4L = 4000mL = 4000g

Title: Re: ppm
Post by: samuch on November 15, 2009, 02:52:56 pm

yeah i get that part but for the concentration?

Quote from: Hielly on November 15, 2009, 02:33:09 pm

would you say the concentration is 4000 ? from water. i got confused here

Title: Re: ppm
Post by: Hielly on November 15, 2009, 03:03:15 pm

i used the formula C= mass of solute in grams/ volume of solution in litress

so now i find C and volume of solution in litres

volume of solution in litres is 88*10^-6

and C=?

is this the right way to do it?

ignore my question samuch, i made a mistake

Title: Re: ppm
Post by: fady_22 on November 15, 2009, 04:41:21 pm

If you are doing it your way, then the concentration would be 88*10^-3 g/ L (you must change the concentration to g/L, by multiplying the concentration by 10^3, if using litres as the volume) and the volume would be 4.0L.
c=m/v
m=c*v
   =88*10^-3*4
   =0.352 g

Title: Re: ppm
Post by: vcesuccess on November 22, 2009, 08:00:37 pm

Our teacher likes to put what we know first then what we have and what we don't know to find out the quantity of unknown such as:
We have            100g in 1000mL
We want to know xg in 1542mL

Use cross multiplication to solve for xg