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Topic: Help with making solutions  (Read 3793 times)

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Offline funboy

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Help with making solutions
« on: January 04, 2007, 07:41:34 AM »
to make 1.0 mol/L of a solution, do you:

take the molecular weight of the substance (ie HCl 36.5 g) add that to a 1 litre container and then top up with water until 1 litre is displaced??

If you are working with a dilute substance (muriatic acid only 31.5% HCl), if you took 100ml of the solution that would give you 31.5ml of HCl then add 900 ml of water and this gives you CLOSE to 1 mol/L

If I use vinegar to make 1.0mol/L of acetic acid??
vinegar only has 5-18% acetic acid, but the molecular weight of acetic acid is 60.05g, so would I have to use 330ml of vinegar to 670ml of water to get 1.0mol/L of acetic acid??

Trying to make a bunch of solutions for an experiment and want to make sure they are correct

« Last Edit: January 04, 2007, 07:57:06 AM by funboy »

Offline Borek

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Re: Help with making solutions
« Reply #1 on: January 04, 2007, 09:29:21 AM »
to make 1.0 mol/L of a solution, do you:

take the molecular weight of the substance (ie HCl 36.5 g) add that to a 1 litre container and then top up with water until 1 litre is displaced??

OK. Although you better start with some water, add acid to it, stirr, then fill up to the mark.

Quote
If you are working with a dilute substance (muriatic acid only 31.5% HCl), if you took 100ml of the solution that would give you 31.5ml of HCl then add 900 ml of water and this gives you CLOSE to 1 mol/L

31.5% of 100 mL will give 31.5 mL only if it is %v/v. HCl is most likely w/w.

Check concentration lectures. CASC will help you too, IIRC you've bought it few months ago ;)

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If I use vinegar to make 1.0mol/L of acetic acid??
vinegar only has 5-18% acetic acid, but the molecular weight of acetic acid is 60.05g, so would I have to use 330ml of vinegar to 670ml of water to get 1.0mol/L of acetic acid??

No idea what you are referring to. Please show your calculations.
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Offline funboy

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Re: Help with making solutions
« Reply #2 on: January 04, 2007, 09:47:21 AM »
where I was going with the vinegar

assuming its 18%

100 ml vinegar = 18ml acetic acid

60/18 = 3.33

3.33 X 100ml = 333 ml of vinegar to get 1 mol of acetic acid

turns out that my vinegar at home was only 5% acetic acid, I dont know how to get 1 mol/L when it would take 1200ml of vinegar to get one mole acetic acid.

Offline Borek

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Re: Help with making solutions
« Reply #3 on: January 04, 2007, 11:13:27 AM »
where I was going with the vinegar

assuming its 18%

100 ml vinegar = 18ml acetic acid

Assuming it is v/v%. Which it probably is not.

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60/18 = 3.33

Only if the density of pure acetic acid is 1 g/mL. It is more like 1.05 g/mL.

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3.33 X 100ml = 333 ml of vinegar to get 1 mol of acetic acid

325mL of 18% w/w if you take density changes into account. Please remember that when mixing liquids sum of volumes is only rarely exactly equal to the final volume.

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turns out that my vinegar at home was only 5% acetic acid, I dont know how to get 1 mol/L when it would take 1200ml of vinegar to get one mole acetic acid.

1M acetic acid is almost 6% w/w, you can't prepare it using less concentrated solution.

Play with CASC, it was written just to help in such calculations.
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