Expressing concentrations as a percent

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To express the concentration of O2 in seawater as a percent, the correct calculation involves converting 5.0 mg O2/L to grams, resulting in 0.005 g. This value is then divided by the total mass of the solution, which is typically considered to be 1 L of water (1,000 g), yielding a concentration of 0.0005 or 0.05%. For the second question, the atmosphere contains 21% O2, so the difference in oxygen concentration between the atmosphere and seawater is approximately 20.95%. The confusion in the calculations stems from incorrect assumptions about the total mass of the solution and the use of atomic mass in the calculations. Accurate understanding of these concepts is essential for proper concentration expression.
Illyaria
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Please post this type of questions in HW section using the template and showing your work.
You measure the concentration of O2 in seawater to be 5.0 mg O2/L H2O. Express this concentration as a percent.

Question 2: The Earth's atmosphere contains 21% O2/L of air. How much more oxygen does the atmosphere hold than seawater from the previous question?

So for question one I got 0.01% which I think is way off. For question 2, I was just going to subtract 21% from the answer from 1. I changed the milligrams to grams for question one.
 
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What was your attempt to solve #1?
 
Comeback City said:
What was your attempt to solve #1?

I converted the 1 5.0 mg to grams and got 0.005g. Then, I divided that by 50 which is the atomic msss for O2/L H2O I think and multiplied that by 100.
 
Atomic mass of Oxygen is 16.00 amu, so O2 would be 32.00. Why did you divide by it though and then multiply by 100?
 

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