The dissolved oxygen concentration of a sample of river water was found to be 8.0 p.p.m - Leaving Cert Chemistry - Question a - 2001
Question a
The dissolved oxygen concentration of a sample of river water was found to be 8.0 p.p.m. Express the concentration of dissolved oxygen in mol dm$^{-3}$.
Worked Solution & Example Answer:The dissolved oxygen concentration of a sample of river water was found to be 8.0 p.p.m - Leaving Cert Chemistry - Question a - 2001
Step 1
Convert p.p.m. to g/dm³
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Answer
The concentration in p.p.m. can be directly converted to g/dm³. Since 1 p.p.m. corresponds to 1 mg/L, we convert 8.0 p.p.m. as follows:
8.0extp.p.m.=8.0extmg/L=0.008extg/dm3
Step 2
Calculate moles from g/dm³
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Answer
To convert grams to moles, we use the molar mass of oxygen, which is approximately 32 g/mol. We calculate the concentration in mol/dm³ as:
ext{Concentration} = rac{ ext{mass in g}}{ ext{molar mass in g/mol}} = rac{0.008 ext{ g}}{32 ext{ g/mol}} = 0.00025 ext{ mol/dm}^3
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