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### Topic: Dilution  (Read 3266 times)

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#### chmdummy1982

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##### Dilution
« on: February 28, 2009, 11:10:37 PM »
I am having trouble with a couple of chemistry problems. One I was able to answer half of, and the other I don't even know how to start. Any help would be greatly appreciated!

Question 1

Use the dilution relationship (Mi x Vi = Mf x Vf) to calculate the volume of 0.500 M NaOH needed to prepare 500 mL of 0.250 M NaOH.

? mL x .500 M NaOH = (500mL x.250M)/.500 = 250 mL

Now here is where I am lost with this problem:

What volume of water would you add to the 0.500 M NaOH volume calculated aove to actually make 500 mL of 0.250 M NaOH?

Question 2
49.22 mL of a 2.01 M NaOH solution reacts completely with 40.28 mL of HCl solution according to the balanced chemical reaction shown below:

HCl (aq) + NaOH(ap) -> NaCl(aq) + H2O(i)

How many moles of HCl reacted?

#### Astrokel

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##### Re: Dilution
« Reply #1 on: February 28, 2009, 11:21:47 PM »
Quote
What volume of water would you add to the 0.500 M NaOH volume calculated aove to actually make 500 mL of 0.250 M NaOH?
You have calculated it! 250mL

Quote
How many moles of HCl reacted?
Check this out, one of this forum admin's website: http://www.chembuddy.com/?left=balancing-stoichiometry&right=ratio-proportions
No matters what results are waiting for us, it's nothing but the DESTINY!!!!!!!!!!!!

#### chmdummy1982

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##### Re: Dilution
« Reply #2 on: February 28, 2009, 11:46:05 PM »
So heres my work.

(40.28 / 49.22) x 2.01 = 986.3590  (thousandths place)

would this be correct?

#### Astrokel

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##### Re: Dilution
« Reply #3 on: March 01, 2009, 12:08:32 AM »
Nope, they are asking for moles of HCl reacted. How do you calculate moles? Any formula you known of that could be apply to this question?
No matters what results are waiting for us, it's nothing but the DESTINY!!!!!!!!!!!!

#### chmdummy1982

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##### Re: Dilution
« Reply #4 on: March 01, 2009, 12:12:05 AM »
Would the molarity formula have anything to do with it?

M = moles of solute/Liters of solution

I'll give it another shot..

(49.22 x 2.01)/40.28 = 2.4561

#### Astrokel

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##### Re: Dilution
« Reply #5 on: March 01, 2009, 12:39:02 AM »
Quote
M = moles of solute/Liters of solution

I'll give it another shot..

(49.22 x 2.01)/40.28 = 2.4561
Formula correct, working wrong. What you are calculating is molarity but they are asking for moles.
No matters what results are waiting for us, it's nothing but the DESTINY!!!!!!!!!!!!

#### chmdummy1982

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##### Re: Dilution
« Reply #6 on: March 01, 2009, 10:39:04 AM »
Would I have to use this equation??

moles = M X V?

#### Astrokel

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##### Re: Dilution
« Reply #7 on: March 01, 2009, 04:46:20 PM »
Yes
No matters what results are waiting for us, it's nothing but the DESTINY!!!!!!!!!!!!