dissolved oxygen in aquatic systems is important for the survival of freshwater fish and they require a minimum of 5 parts per million(ppm) of dissolved oxygen (02) in a stream lake to survive. although this amount seems small,
how many oxygen molecules are in a litre of water containing oxygen at the concentration of 5ppm?
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To calculate the number of oxygen molecules in a liter of water containing oxygen at a concentration of 5 parts per million (ppm), we first need to understand the relationship between ppm and moles.
1 ppm means that there is 1 molecule in every 1 million molecules present. In other words, 1 ppm is equivalent to 1 part in 1 million parts.
To convert from ppm to moles, we need to know the molar mass of oxygen, which is approximately 32 g/mol.
Here's how we can calculate the number of oxygen molecules in one liter of water:
1. Convert the concentration from ppm to a decimal fraction:
5 ppm = 5/1,000,000 = 0.000005 (decimal fraction)
2. Calculate the number of moles of oxygen in the water:
0.000005 x 1 liter = 0.000005 moles
3. Convert moles to number of molecules:
0.000005 moles x 6.022 x 10^23 molecules/mol = 3.011 x 10^19 molecules
Therefore, in a liter of water containing oxygen at a concentration of 5 ppm, there are approximately 3.011 x 10^19 oxygen molecules.