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Topic: Finding the mass in an solution  (Read 15062 times)

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Offline ILoveISO

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Finding the mass in an solution
« on: February 01, 2010, 08:34:51 PM »
How does one find how much mass there is in a given solution? Specifically how would I find the mass of sodium carbonate in a 250ml solution? What info would I need? Thanks not sure how to get started
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Offline ILoveISO

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Re: Finding the mass in an solution
« Reply #1 on: February 01, 2010, 09:59:48 PM »
This is what I tried...

I took the moles of NaOh required for the back titration and multiplied it by 1/2 (mole bridge) someone check if this is right? Then I multiplied it by 10 because I only used 25.00ml of it per titration then the answer from that I multiplied by the molar mass of Na2CO3... is this correct?

2NaOH + H2SO4 --> 2H2O + Na2SO4

and

H2SO4 + Na2CO3 --> Na2SO4 + H2O + CO2
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Offline Schrödinger

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Re: Finding the mass in an solution
« Reply #2 on: February 01, 2010, 10:08:03 PM »
I'm really sorry, but we can't help you unless you :

1. Post the entire question properly
or
2. Post some sort of a general doubt that is related to your question, that might help you solve it.

Your second post leaves us in no man's land, as we have no clue as to what is happening.
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Offline ILoveISO

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Re: Finding the mass in an solution
« Reply #3 on: February 01, 2010, 10:47:36 PM »
The question just says to find the mass of sodium carbonate in 250.0ml of solution... what more do you need
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Offline Schrödinger

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Re: Finding the mass in an solution
« Reply #4 on: February 01, 2010, 10:49:53 PM »
You will need to know the concentration of the solution

Read http://en.wikipedia.org/wiki/Concentration
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"Destiny is not a matter of chance; but a matter of choice. It is not a thing to be waited for; it is a thing to be achieved."
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Offline ILoveISO

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Re: Finding the mass in an solution
« Reply #5 on: February 01, 2010, 11:05:16 PM »
What do I do after I find the conc of the solution
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Offline Black Mage

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Re: Finding the mass in an solution
« Reply #6 on: February 01, 2010, 11:11:11 PM »
Quote from: ILoveISO on February 01, 2010, 11:05:16 PM
What do I do after I find the conc of the solution
Assuming you are given a Molarity value, you will need to take that value and plug it into the Molarity equation with the other information you know.

http://en.wikipedia.org/wiki/Concentration#Molarity

What is the unknown value in that?

How might you get from that unknown value to a mass?

Give it a try and see where you get to.
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Offline ILoveISO

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Re: Finding the mass in an solution
« Reply #7 on: February 01, 2010, 11:22:48 PM »
I find the moles of sodium carbonate in 0.250L of solution then divided it by 0.0250L to get M

Then I multiplied 0.0250L to get moles and multiplied it by the molar mass of Na2CO3... is this right? I tried =/
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Offline Black Mage

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Re: Finding the mass in an solution
« Reply #8 on: February 01, 2010, 11:35:27 PM »
As Schrödinger said, it is difficult to help without being able to see the whole full initial question.

But if you have

M = mol / L

And you put in the information you gave, you would need to multiply both side of the above equation by the volume (L) to get the mol of sodium carbonate.

Stoichiometry is then needed to convert that to grams, so you were right, you just did the math wrong to solve for the mol.

This seems like a titration problem though so it is probably not as simple as that, but I can't know without a clear initial problem.
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Offline ILoveISO

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Re: Finding the mass in an solution
« Reply #9 on: February 01, 2010, 11:56:00 PM »
What initial problem...? I'll type all the other Q's before it and you tell me which part is needed?

1. Calculate the moles of sulfuric acid present in the 50ML standard acid solution
2. Calc the avg volume of NaOH required for the back titration
3. Calc the moles of NaOH required for back titration
4. Calc the moles of sulfuric acid that remained in solution after reaction with carbonate
5. Calc the moles of sulfuric acid that reacted with the carbonate
6. Write the balanced equation for sulfuric acid reacting with sodium carbonate
7. Calculate the moles of sulfuric acid in 25ML aliquot of solution
8. Calculate the moles of sulfuric acid in 250ML solution

9. Calculate the mass of sodium carbonate present in 250ML solution
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Offline Black Mage

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Re: Finding the mass in an solution
« Reply #10 on: February 01, 2010, 11:59:58 PM »
Quote from: ILoveISO on February 01, 2010, 11:56:00 PM
What initial problem...? I'll type all the other Q's before it and you tell me which part is needed?

1. Calculate the moles of sulfuric acid present in the 50ML standard acid solution
2. Calc the avg volume of NaOH required for the back titration
3. Calc the moles of NaOH required for back titration
4. Calc the moles of sulfuric acid that remained in solution after reaction with carbonate
5. Calc the moles of sulfuric acid that reacted with the carbonate
6. Write the balanced equation for sulfuric acid reacting with sodium carbonate
7. Calculate the moles of sulfuric acid in 25ML aliquot of solution
8. Calculate the moles of sulfuric acid in 250ML solution

9. Calculate the mass of sodium carbonate present in 250ML solution
See how this is a multi-step problem?

Its important to go step by step because one step in many cases will allow for the next step to be solved.

Sorry because that is not the answer you are looking for but giving you the answers is not going to help you.
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"Let the future tell the truth and evaluate each one according to his work and accomplishments. The present is theirs; the future, for which I really worked, is mine." - Nikola Tesla

Offline ILoveISO

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Re: Finding the mass in an solution
« Reply #11 on: February 02, 2010, 12:04:55 AM »
WEll can you at least guide me thru it? I have the answers before this Q so which ones should I start off with?
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