Molarity and Dilution

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Chem_Mod
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Molarity and Dilution

Postby Chem_Mod » Wed Apr 24, 2013 9:44 pm

A solution is prepared by dissolving 55.1 g of KCl in approximately 75 mL of water and then adding water to a final volume of 125 mL. What is the molarity of KCl(aq) in this solution?

Chem_Mod
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Re: Molarity and Dilution

Postby Chem_Mod » Wed Apr 24, 2013 9:45 pm

molarity of KCl(aq)=55.1g/(74.5513g/mol)/(0.125L)=5.91 mol/L (assuming 75 ml of water is an aliquot of water).

Kevin Hernandez 3A
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Re: Molarity and Dilution

Postby Kevin Hernandez 3A » Wed Oct 04, 2017 7:26 pm

Why is this problem not a Mi * Vi= Mf* Vf, if it is giving you the final volume (125ml).

Yixin Angela Wang 2H
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Re: Molarity and Dilution

Postby Yixin Angela Wang 2H » Wed Oct 04, 2017 10:21 pm

Molarity is moles of solute/volume of solution. The Mi*Vi = Mf*Vf is dilution, which is not what this particular problem is asking. To solve this problem, you first convert grams of KCl to moles by dividing the mass by the molar mass. Then, you divide the number of moles by the volume in liters, which would be 0.125L. The quotient would be your molarity.

DavidEcheverri3J
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Re: Molarity and Dilution

Postby DavidEcheverri3J » Thu Oct 04, 2018 2:15 pm

So the 75 mL of the original solution is not required to solve the final molarity?

Liza Hayrapetyan-3K
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Re: Molarity and Dilution

Postby Liza Hayrapetyan-3K » Fri Oct 12, 2018 9:27 am

No, because it mentions how the final volume BECOMES 125 mL meaning it replaces the 75 mL. I think that part was meant to test us.

SummerLee1F
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Re: Molarity and Dilution

Postby SummerLee1F » Fri Oct 12, 2018 9:45 am

I would use the equation Minitial x Vinital = Mfinal x Vfinal, based on the information we are given.

Yixiao Hu 3C
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Re: Molarity and Dilution

Postby Yixiao Hu 3C » Sat Oct 13, 2018 3:13 pm

molarity=m(kcal)/M(kcal)/V(KCL)

Ronald Thompson 1F
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Re: Molarity and Dilution

Postby Ronald Thompson 1F » Sat Oct 13, 2018 3:29 pm

If done correctly, should I have gotten 5.92?
I also was not entirely sure how to implement Mi x Vi = Mf x Vf

Dakota Walker 1L
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Re: Molarity and Dilution

Postby Dakota Walker 1L » Thu Oct 10, 2019 1:54 pm

I still don't understand why this isn't a dilution when a 75mL solution was created at first, then this same solution was diluted to get a 125mL solution. In what way would a dilution problem be written differently?

Justin Quan 4I
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Re: Molarity and Dilution

Postby Justin Quan 4I » Thu Oct 10, 2019 2:17 pm

For this problem, you do not use M1V1=M2V2 because there’s no initial or final molarity or volume. It’s simply just moles/(total volume). The total volume being 125ml.


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