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Procedure in G21/G23

Posted: Sun Oct 06, 2019 10:58 am
by Jessica Chen 2C
In order to solve these problems, I went through a (probably unnecessarily) long process of first finding the mass percentage of the ions, multiplying that number by the mass, dividing that by molar mass to get moles, and then adding up all the moles if necessary, before finally dividing by volume to get molarity. I technically got the right answer, but I feel like my procedure isn't the most efficient to use during a test. When I checked the solution manual, they indeed had a shorter method. They just divide the mass of the compound by the molar mass of the compound, and multiply by a molar ratio if necessary, before adding them up and dividing by volume to get molarity.
However, I'm having a difficult time understanding why this works. Can someone explain why you can just convert the compound to moles, instead of finding the mass of the ion first?

Re: Procedure in G21/G23

Posted: Sun Oct 06, 2019 11:15 am
by Anika Chakrabarti 1A
Since the problems start out by giving us the mass of the compounds, I just started out by converting everything to moles. Once you know the moles, then the rest can be figured out by using mole ratios since now the different substance amounts can be compared to each other.