Hi all,
If my tap water has a reading of 600ppm as far as I'm aware it has 600 parts per million, could someone explain this a little further.
PPM is just a way of describing relatively dilute solutions.
Jose is right, 1mg per litre is 1 ppm and 1g per litre is 1000 ppm. You could present the same value as percentages or decimals, but they are more difficult to interpret.
If you use scientific notation I think it becomes easier. Percentages are parts per 100 (10^2), but we can have parts per thousand (10^3), parts per million (10^6), or parts per billion (10^9).
A lot of our students struggle with this, so I give the students a spreadsheet with a periodic table, numbers expressed as powers of 10 from 10^-9 to 10^9, and some examples, and formulae, that allows them to convert from ppm to mols, and from ppm to grams for any dilution of a stock solution
If you are talking about ppm "TDS"?, that is actually a measure of conductivity, where all the ions in solution are linearly related to electrical conductivity, expressed as ppm "total dissolved solids" (conductivity multiplied by a conversion factor, usually 0.64).
If we assume there really are 600 parts per million of all the ions in solution, that is 600 in 1,000,000 (10^6), knocking 2 noughts off either side, gives us 6 parts in 10,000 or 0.6g of salts in 1 litre (1000g) .
TDS is a measure of all the ions, but we could use analytical techniques like "atomic absorption spectrophotometry", "mass spectrometry" etc. to get a value for an individual element.
cheers Darrel