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Topic: I am Stumped need help with Zinc Chlride Emperical Formula!!  (Read 27791 times)

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Offline Hoffmann21

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I am Stumped need help with Zinc Chlride Emperical Formula!!
« on: January 17, 2008, 10:55:11 PM »
ok, i have a lab due and i know THIS IS not cheating just looking for help.

this is what i got.

Mass of labeled Beaker   50.29g
Mass of beaker + zinc   51.18g
Mass of beaker + zinc chloride   52.14g
Mass of beaker + zinc chloride(2nd trial)   52.14g


Calculations:
1a. Calculate the mass of zinc that reacted. Include descriptions with this calculation.
   Mass of labeled beaker +zinc – mass of the labeled beaker.
   51.18g – 50.39g= .89g of zinc
b. Calculate the number of moles of zinc.
   (Zinc)=(1 mole)
1   Mole of zinc
(.89g)= ( 1 mole)=0.0136 = 0.014
1   65.4
2.) Calculate the mass of zinc cloride that was produced. Include descriptions with this calculation.
   Mass of beaker + zinc chloride- Mass of beaker + zinc
   52.14g – 51.18g=0.96g
3a) Calculate the mass of chlorine in the zinc chloride. Include descriptions with this calculation.
   Mass of Zinc Chloride- mass of Zinc= Mass of chlorine
      0.96-.89=0.07g of chlorine
3b) Calculate the number of moles of chlorine.
   
(0.07)=(1 mole)=0.002g
    1        35.45

4.) Determine the ratio: Moles Cl. This ratio should be close to a whole number.
                                         Moles Zn
 ---0.002g=0.14
     0.014

Offline Hoffmann21

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Re: I am Stumped need help with Zinc Chlride Emperical Formula!!
« Reply #1 on: January 17, 2008, 10:57:07 PM »
somthing is not right!

Why is my Mole for Chlorine so low?

my ratio should be close to a whole number. its not. i need help.

Dont give me a answer just a tip on whats wrong thanks!

Offline Hoffmann21

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Re: I am Stumped need help with Zinc Chlride Emperical Formula!!
« Reply #2 on: January 17, 2008, 11:26:38 PM »
please someone help its urgent!! =] :o

Offline Alpha-Omega

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Re: I am Stumped need help with Zinc Chlride Emperical Formula!!
« Reply #3 on: January 17, 2008, 11:42:44 PM »
OK I adjusted where you made mistakes...you did alot of work...made 2 mistakes....I labeled them OK....


Calculations:
1a. Calculate the mass of zinc that reacted. Include descriptions with this calculation.
   Mass of labeled beaker +zinc – mass of the labeled beaker.

   51.18g – 50.39g= 0.89g of Zn  Actual RXN in beaker

b. Calculate the number of moles of zinc.
   (Zinc)=(1 mole) = 65.39 g

Wt. zinc = 65.39g/mol (from the periodic table)

1Mole of zinc
(0.89 g Zn ) x (1 mole Zn/65.39g) = 0.0136 mole Zn (you are rounding off too soon-wait until the end)

2.) Calculate the mass of zinc chloride that was produced. Include descriptions with this calculation.

   
Mass of beaker + zinc chloride - mass of empty labeled beaker....

HERE WAS YOUR FIRST MISTAKE: 

52.14g – 50.29g=1.85g ZnCl2  (this is your formula for zinc chloride ZnCl2-it is the accepted formula for zinc chloride)

3a) Calculate the mass of chlorine in the zinc chloride. Include descriptions with this calculation.

Mass of Zinc Chloride - mass of Zinc= Mass of chlorine

HERE WAS THE OTHER MISTAKE:

1.85 g ZnCl2 X 1 mole ZnCl2/136.28g/mole x (2 mole Cl/1 mole ZnCl2) x 35.45 g Cl/ 1 mole Cl = 0.96426 g Cl

3b) Calculate the number of moles of chlorine.

Wt. Cl = 35.45 (from the periodic table)
   
(0.96426 g Cl) x (1 mole Cl/35.45 g Cl)= 0.02715 mole Cl
   

4.) Determine the ratio: Moles Cl. This ratio should be close to a whole number.
                                       
The accepted formula for ZnClx = ZnCl2…you have to find X
 Moles Zn

Now round off  0.014 mol Zn   and 0.0271 mol Cl

0.014/0.014 = 1 

0.027/0.014 = 1.9 ….= 2

Your formula is ZnCl2

ADDENUDM:

If you are determining from your Actual exp results:

If these are actual EXPERIMENTAL RESULTS if you actually performed this rxn in a beaker….which is not stated in the problem…and you are not determining this theoretically-MY MISTAKE….Thought it was a prelab....

I thought you were doing a prelab determining this theoretically and not by actual exp....since none of the

Part 1 -51.18 g with Zn in beaker only....(zinc metal shavings?)

Part 2- your Reaction (added a white powder?) leaves you with 52.14 g


You will be left with:
 
52.14 – 51.18 = 0.96g Cl....since this is now termed part 2 of actual reaction....you have accounted for the difference in the beaker containing zinc and the beaker that now contains the zinc chloride....where you added Cl to your rxn mixture..

The determination of weight is just successive subtractions....

EMPTY BEAKER = 50.29 g
Beaker with Zn = 51.18 g
Weight of Zn = 51.18 g - 50.29 g = 0.89 g
Beaker with Zin chloride (part 2 of Rxn)= 52.14 g
Weight of Chloride = 52.14 - 51.18 g = 0.96g

51.18 g - 50.29 g = 0.89 g Zn

0.96 g Cl since rxn took place in your beaker....according to Borek/if this was by actual EXP  use your data as follows.

0.96 g Cl (1mole Cl/35.45 g) = 0.027 mol Cl

0.027 mol CL

0.027/0.014 = 1 .92857 for your Cl

0.014 mol Zn

0.014/0.014 = 1.9688 = 1  for your Zn

In this case you still have your ratios 1:2 for Zn:Cl

ZnCl2

You did a double subtraction when you said 0.96 - 0.89 = 0.07
« Last Edit: January 18, 2008, 08:56:03 AM by mebecker1 »

Offline Borek

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Re: I am Stumped need help with Zinc Chlride Emperical Formula!!
« Reply #4 on: January 18, 2008, 03:27:58 AM »
Mass of Zinc Chloride - mass of Zinc= Mass of chlorine

HERE WAS THE OTHER MISTAKE:

1.85 g ZnCl2 X 1 mole ZnCl2/136.28g/mole x (2 mole Cl/1 mole ZnCl2) x 35.45 g Cl/ 1 mole Cl = 0.96426 g Cl

This is not a mistake, he determines mass of chlorine based on experimental data, not on known composition.

2.) Calculate the mass of zinc cloride that was produced. Include descriptions with this calculation.
   Mass of beaker + zinc chloride- Mass of beaker + zinc
   52.14g – 51.18g=0.96g

This is mass of chlorine, not of zinc chloride.
« Last Edit: January 17, 2012, 10:48:27 AM by Arkcon »
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