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Topic: how to determine the mass ratios of a compound  (Read 4915 times)

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Offline Mr_Man

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how to determine the mass ratios of a compound
« on: April 01, 2007, 02:24:06 AM »
i got question in an assignment where i have to design a method to find mass ratios of X to Cl in a substance XCl. (X is obviously a group 1 cation, eg K, Na, Cs, ect.). so the substance is one of a few things

my thoughts on this is that I find out the weight of either Cl or X in a certain amount of the substance and from this this a ratio can easily be determined. so if i got 10 g of the substance and knew that 6 grams of it was Cl, through a test, then i could determine that X is Na or something like that But how??? i dont know anything about titration although i have red it can be used to do this

also i have red about a flame test which can be used to determine this same thing but doesnt give definite answers. eg, Cs and K produce a very similar flame color which makes it hard to tell which element it is

so can someone help me? is there a method that can do this

note: i have only been doing chem (yr 11) for a couple months so if you go super indepth to a uni level then i dont think i could follow.

Offline Ψ×Ψ

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Re: how to determine the mass ratios of a compound
« Reply #1 on: April 01, 2007, 02:35:23 AM »
I think I did a gravimetric lab using AgCl (not-so-soluble ;) ) to do that.  It's been a while.

Offline Mr_Man

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Re: how to determine the mass ratios of a compound
« Reply #2 on: April 01, 2007, 02:44:11 AM »
sorry, but what does that mean??? (using a gravimetric lab)

did it work? was it acurate?

allanf

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Re: how to determine the mass ratios of a compound
« Reply #3 on: April 01, 2007, 02:56:37 AM »
Gravimetric means by mass.  The idea is that you would take your solution of XCl, add some silver (say silver nitrate AgNO3) in excess which would cause the all the chloride ions to come out of solution as silver chloride precipitate, which you then weigh.

The difficulty in this is ensuring that the precipitate is very dry when it is weighed, and that it formed particulates large enough to be filtered, but this isn't usually a big problem.  You could also consider a titration, perhaps using an electrode of some sort to indicate the end point.

Offline Borek

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Re: how to determine the mass ratios of a compound
« Reply #4 on: April 01, 2007, 03:12:00 AM »
You could also consider a titration, perhaps using an electrode of some sort to indicate the end point.

Google for Mohr and Volhard's methods of chloride determination.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Mr_Man

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Re: how to determine the mass ratios of a compound
« Reply #5 on: April 01, 2007, 06:35:41 AM »
Gravimetric means by mass.  The idea is that you would take your solution of XCl, add some silver (say silver nitrate AgNO3) in excess which would cause the all the chloride ions to come out of solution as silver chloride precipitate, which you then weigh.

The difficulty in this is ensuring that the precipitate is very dry when it is weighed, and that it formed particulates large enough to be filtered, but this isn't usually a big problem.  You could also consider a titration, perhaps using an electrode of some sort to indicate the end point.

if i were to take this route what would be the most accurate way of weighing the precipitate??? would one of those scales with all those sliding weights be the most accurate? (sorry i forgot the name)

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