[shiftthatbogie]

Ive had to answer a 4 part question and am stuck on the last part. Il show the whole lot incase I have gone wrong in the first parts..

A. A contaminated lake is 175m long, 40m wide and with an average depth of 7.5m. What is the volume of the lake in m³?

 175 x 40 x 7.5 = 52,500 m³

B. What is the volume of the lake in cm³?

  52,500 x 100 x 100 x 100 = 5.25 x 10¹⁰ cm³

C. The concentration of Cu on the lake is 85ppb what is this in mol/kg? Atomic mass of Cu is 63.545 g/mol

  85ppb / (1x10⁶) = 8.5 x 10^-6 g/kg
 
  8.5 x 10^-6 / 63.545 = 1.338 x 10^-7 mol/kg

D. How many moles of dissolved Cu are there in the lake? Density of lake water is 1005 kg/m³

I have no clue where to start with this, any help would be appreciated, also if I have done the first parts wrong could someone tell me where I have gone wrong. Thanks

[sjb]

In the first case, ppb is not 10⁶. Whether it's 10⁹ or 10¹² may depend on where you are in the world, but even allowing for that, check your exponents.

for D, you have the volume of the lake in A, so you can calculate the total mass of the lake given your density, and as you have a concentration in C, you can calculate the number of moles of copper

[shiftthatbogie]

Ive tried, but I dont know how to work out the number of moles from concentration and mass? ive worked out the mass as 1005x52,500 = 52762500 but I dont know what to do with that and the concentration to get the number of moles?
Thanks

[Borek]

If there is 65x10^-9 kg of Cu in 1 kg of water, how much is in 2 kg? 10? 52762500?

63.5 g Cu - how many moles it is? (And no, I am not suggesting there is 64.5 g of copper in the lake, it was just a first number that come to my mind when I heard about moles of copper).