Expressing concentrations as a percent

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Discussion Overview

The discussion revolves around expressing concentrations as a percentage, specifically focusing on the concentration of oxygen in seawater and comparing it to the concentration of oxygen in the Earth's atmosphere. The context includes mathematical reasoning and problem-solving related to chemistry.

Discussion Character

  • Mathematical reasoning, Homework-related

Main Points Raised

  • One participant measured the concentration of O2 in seawater as 5.0 mg O2/L H2O and initially calculated it as 0.01% but expressed uncertainty about this result.
  • Another participant inquired about the method used to solve the first question, seeking clarification on the calculations performed.
  • A different participant converted 5.0 mg to grams, obtaining 0.005 g, and mentioned dividing by the atomic mass of O2 (32.00 g/mol) and multiplying by 100, although the reasoning for this approach was questioned.
  • There was a correction regarding the atomic mass of O2, with a participant stating it is 32.00 amu, but the rationale for the division in the calculation was unclear.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the correct method for calculating the percentage concentration of O2 in seawater, and there are differing approaches and uncertainties regarding the calculations.

Contextual Notes

There are unresolved aspects regarding the assumptions made in the calculations, particularly the conversion from milligrams to grams and the application of the atomic mass in the percentage calculation.

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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