[kerilynn]

A saturated solution of PbCO3 contains 0.00011 g PbCO3 in 100 g of water. What is this concentration in parts per million?


can you please work this out for me

[Hapto]

Parts per million is the same thing as milligrams per liter.

[Borek]

Parts per million is the same thing as milligrams per liter.

We have been there zillion times. This is only approximation. Besides, it is not necessary here, as kerilynn had the amount of water given as mass, not as volume.

[Hapto]

A zillion times?

Parts per million (ppm), is a ratio of parts of solute to one million parts of solution, and is usually applied to very dilute solutions. It is often found in reports of concentration of water contaminants.
To calculate parts per million, divide the mass of the solute by the total mass of the solution. This number is then multiplied by 106 and expressed as parts per million (ppm). In dilute water solutions, we can assume that 1 mL of water-based solution has a mass of 1 gram, so 1 liter of solution has a mass of 1000 grams.

http://www.sciencegeek.net/Chemistry/taters/Unit6SolutionConcentration.htm


Most practicing chemists wouldn't split hairs over the difference between 0.00011 grams dissolved in 100 mL of water (a total of 100.00011 grams of solution) and 0.00011 grams per 100 mL of water (a total of 100 grams of solution).

For this example it is entirely appropriate to assume that the density of the solution is equal to that of pure water and to equate one liter of water with 1 kg of water.

[Borek]

A zillion times?

Yes, search forums.

Most practicing chemists wouldn't split hairs over the difference between 0.00011 grams dissolved in 100 mL of water (a total of 100.00011 grams of solution) and 0.00011 grams per 100 mL of water (a total of 100 grams of solution).

As long as we are talking about diluted water solution, this approach is OK, but will you also say that 1 ppm of iron in concentrated sulfuric acid (density over 1.8 g/mL) is 1 mg per L? And ppm is how the concentration of heavy metals will be given in high purity reagents. You have not stated "in diluted water solution", your definition was very strong - 1 mg per liter, regardless of the circumstances.

Problem is not with using such approximations, they are very usefull, problem is students tend to learn such definitions (like 1mg/L) not understanding their range of application. And unfortunately students who learnt wrong tend to be wrong for ever.

[Hapto]

Parts per million is the same thing as milligrams per liter... in this example.

Jeesh!

[DrCMS]

Hapto wind your neck in, you're new so we'll cut you some slack but Borek is right. 

Parts per million is the same thing as milligrams per liter... in this example.

Jeesh!

you missed the "in this example" part when you made your original statement and has already be said it is irrelevant in this example as the weight of solution is given not the volume.

However, kerilynn has been given the definition of ppm multiple times and all she wants is someone to give her the answer rather than do any work herself.

So kerilynn I'll say it again STOP being lazy and do your homework YOURSELF!

[enahs]

If I replace your water with acetonitrile then your 1mg/L is automatically off by ~25%, methanol %20%, 34^oC water and average salt concentration in sweat (i.e. Sweat) 4% off.