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Midterm Prep Worksheet- Molarity

Posted: Sun May 06, 2018 10:34 pm
by Emely Reyna 1F
One of the questions on a UA worksheet asked to find the molarity of 55.1 g of KCl that was dissolved approximately in 75ml of water and then added to a final volume of 125mL. Trying the problem on my own I initially added the volumes together but when going over the question we used only the final volume of 125 mL, why is this case?

Re: Midterm Prep Worksheet- Molarity

Posted: Sun May 06, 2018 10:36 pm
by Danielle Sumilang - 1F

I don't think the 75 ml volume is relevant because the final volume of the solute was 125 ml. Therefore, 125 ml is used in the equation to find the molarity.

Re: Midterm Prep Worksheet- Molarity  [ENDORSED]

Posted: Sun May 06, 2018 10:37 pm
by RubyLake1F
I think that this problem is somewhat trying to trick you by giving you the initial volume when it really isn't necessary. You started with 75 mL and water was added until the volume was 125 mL (which means that 50 mL was added). What matters is that in the end you have a total of 125 mL (not 125 plus the original 75), so you actually don't need to combine any volumes because they give you the final volume. This means that molarity is equal to (moles of solute) divided by (.125 L).