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Author Topic: Solutions Problems  (Read 4184 times)

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dgolverk

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Solutions Problems
« on: December 16, 2007, 08:26:11 AM »

Hello,
I study for my unit test and I need your help in these 2 questions:
1)A teaspoon of milk magnesia contains 12mg of magnesium hydroxide. What volume of 0.01mol/L HCl in a person's stomach would be neutralized by this teaspoon of antacid?
*I was thinking of creating an equation but I am not sure what to do next.
I also figured out that the number of moles of Mg(OH)2 is 2.07x10exp-4 mol.

2) Some commercial bleach solutions contain 5.25% W/V sodium hypochlorite. Calculate the sodium hypochlorite concentration in mol/L.
*I know that the formula is %C=W/V.
so 0.0525=W/V but have no idea what to do next.

Thank you very much,
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Yggdrasil

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Re: Solutions Problems
« Reply #1 on: December 16, 2007, 08:40:13 AM »

1)  Start with a balanced chemical reaction.  From this reaction, figure out how many moles of HCl are neutralized by 2.07x10-4 mol of magnesium hydroxide.

2)  What is 5.25% (w/v) in g/mL?  Convert grams to moles then mL to L.
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dgolverk

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Re: Solutions Problems
« Reply #2 on: December 16, 2007, 08:56:07 AM »

so thats my answer for 1:
Mg(OH)2 + 2HCl --->  MgCl2 + 2H2O
1/2.07x10-4 = 2/X
X=4.14 mol oh HCl needed to neutralize.

and 2:
5.25g/100mL
Moles of NaClO=0.070mol
C=n/v
C=0.070mol/0.1L
C=.70mol/L

Is that right?
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Yggdrasil

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Re: Solutions Problems
« Reply #3 on: December 16, 2007, 09:11:56 AM »

1)  You mean 4.14x10-4 mol of HCl, right?  Remember that the question asks for the volume of a 0.01mol/L HCl solution that would be neutralized by the magnesium hydroxide, so you still need to do one more step.

2)  Correct.
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dgolverk

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Re: Solutions Problems
« Reply #4 on: December 16, 2007, 09:18:48 AM »

Oh right.
So C=n/v
0.01mol/L = 4.14x10-4mol/v
v = 0.04L

Thank you :)
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