ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: kaanonball on December 30, 2008, 06:37:29 pm

Title: Finding the chemical equation
Post by: kaanonball on December 30, 2008, 06:37:29 pm: Greetings everyone, i've been sitting here for a while trying to figure out what chemical equation places all the information together.. and so far no luck as i'm not to sure what by ﬁrst precipitating the calcium ions present as calcium oxalate means..

hmm any help would be appreciated :D

The Question
The calcium content of a sample can be determined gravimetrically by ﬁrst precipitating the calcium ions present as calcium oxalate.
When this precipitate is heated, it decomposes completely to produce calcium oxide. In testing the purity of a calcium chloride sample, a chemist used gravi-
metric analysis and obtained 8.81 g of calcium oxide from an original 18.0 g sample of calcium chloride.

Calculate the percentage purity of the calcium chloride.
Title: Re: Finding the chemical equation
Post by: beezy4eva on December 30, 2008, 06:54:49 pm: precipitating the calcium ions (Ca+) as calcium oxalate (CaC2O4) means that any calcium ions present in an aqueous sample (ie a sample of something thats been dissolved,normally in water) become the precipitate (ie a solid) calcium oxalate. So we assume that the original 18.0g sample of CaCl was first dissolved.

equation you'll need:
2CaC2O4 (s) + O2 (g) --> 2CaO(s) + 4CO2(g)

You wont need an equation for the precipitation process.

Hints:
-You can calculate the number of mole of calcium ions that were precipitated by using the formula n(moles)=mass/molar mass
-Once you know the n of Ca+ that was in the solution of dissolved CaCl, you can calculate the mass of CaCl that was present in the CaCl
Title: Re: Finding the chemical equation
Post by: kaanonball on December 30, 2008, 07:14:34 pm: ty very much =]

got it now
Title: Re: Finding the chemical equation
Post by: methodsboy on December 30, 2008, 07:48:00 pm: wha? u guys already got gravimetric hw?
i just got yr11 revision
Title: Re: Finding the chemical equation
Post by: hard on December 30, 2008, 08:43:05 pm: Quote from: methodsboy on December 30, 2008, 07:48:00 pm
wha? u guys already got gravimetric hw?
i just got yr11 revision
same
but i'm not going to do the year 11 revision. I'm just going to start the book already cbfed doing n=cv n=m/M etc 1000 times over.
Title: Re: Finding the chemical equation
Post by: kaanonball on December 31, 2008, 02:03:24 am: we didn't get it as homework.. i thought i would just get ahead ;)
Title: Re: Finding the chemical equation
Post by: AQ on December 31, 2008, 09:20:40 am: gravimetric????

thats unit 3 i guess.

btw, what book are you guys using?
were using heinemann.
Title: Re: Finding the chemical equation
Post by: kaanonball on December 31, 2008, 01:18:51 pm: Quote from: AQ on December 31, 2008, 09:20:40 am
btw, what book are you guys using?
were using heinemann.

we are using the StudyOn Chemistry book by jacaranda
Title: Re: Finding the chemical equation
Post by: methodsboy on December 31, 2008, 01:29:09 pm: we're using heinemann too
Title: Re: Finding the chemical equation
Post by: NE2000 on January 01, 2009, 04:43:20 pm: Quote from: kaanonball on December 31, 2008, 01:18:51 pm
Quote from: AQ on December 31, 2008, 09:20:40 am
btw, what book are you guys using?
were using heinemann.

we are using the StudyOn Chemistry book by jacaranda

How is that?
Title: Re: Finding the chemical equation
Post by: kaanonball on January 01, 2009, 04:51:19 pm: Quote from: NE2000 on January 01, 2009, 04:43:20 pm
How is that?

It's quite good, decent examples and a lot of explanation... But sometimes they blabber on for about 2 pages before they get to the point, but otherwise it's quite good.