Determing the mass percent of chloride from a mixture of NaCl and KCl salts

In summary, the experimenter found that the mass percent of chloride in a sample varied widely depending on the technique used, even though the mixture's total mass and mole amounts were the same.
  • #1
waqaszeb
11
0
Hi guys,

I am doing a lab experiment which involves analysis of a sample of a mixture of NaCl and KCl. I'm using volumetric titration ( Mohrs and Fajans methods) as well a Gravimetric analysis technique. The underlying idea is determine the mass percent of chloride in the same sample using different techniques to see which one is better. The mass percent of the sample, regardless of the method employed, should be similar but the results I found are extremely off. I'm not sure what I am doing wrong.

For example:

For Fajan's method:

Trial 1: 14.31 mL of silver nitrate were needed to reach equivalence point. So I determine the mass(%) chloride in the following way:

14.31 mL/ 1000 x 0.1 M Silver Nitrate = 0.00143 moles of Silver Nitrate

1:1 ratio so the moles of chloride must be equal to the moles of Ag.

moles(chloride)=0.00143 moles x 35.453 g/mol = 0.050 grams?

how is that possible, though? the initial mass of the mixture was 0.1083 grams which was used to make a 250 mL solution. I then did three trials of titration using 25 mL aliquots..each 25mL aliquot should contain 0.01083 grams of mixture...how is it that the mass of just chloride alone is more than mass of the entire mixture. (0.050/0.01083) x 100 = 461% mass. this is obviously wrong. i don't get it :S

In addition, from the gravimetric analysis procedure, I got a mass percent chloride of 58.3. That seems realistic, and I think Fajan and Mohr mass percent should be in that range..not 461% lol. Can anybody help? Thanks!
 
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  • #2
waqaszeb said:
the initial mass of the mixture was 0.1083 grams

Really that low? If I am not mistaken that would mean you were aiming at using less than 2 mL of the titrant, doesn't make any sense to me.
 
  • #3
Sorry, you're right. Its not 0.1083 but 1.0083 grams
 
  • #4
That puts your results in the same ballpark, doesn't it?
 
  • #5
Yes it does, thank you for pointing this out! wow..one whole day wasted on trying to figure out why i was so dumb..
 
  • #6
waqaszeb said:
one whole day wasted on trying to figure out why i was so dumb..

Welcome to the club :wink:
 

1. How do you determine the mass percent of chloride from a mixture of NaCl and KCl salts?

To determine the mass percent of chloride, you will need to first measure the total mass of the mixture. Then, you will need to separate the mixture into its individual components, NaCl and KCl. Next, you will need to determine the mass of chloride in each component by multiplying the mass of the component by its percent composition of chloride. Finally, add the mass of chloride from each component and divide it by the total mass of the mixture, then multiply by 100 to get the mass percent of chloride.

2. Why is it important to determine the mass percent of chloride from a mixture of NaCl and KCl salts?

Determining the mass percent of chloride in a mixture of NaCl and KCl salts is important for several reasons. It allows you to accurately calculate the amount of chloride present in the mixture, which is important for understanding its properties and potential uses. Additionally, knowing the mass percent of chloride can also help in determining the purity of the mixture and ensuring it meets certain standards or regulations.

3. What tools and materials are needed to determine the mass percent of chloride from a mixture of NaCl and KCl salts?

To determine the mass percent of chloride, you will need a balance or scale to measure the total mass of the mixture, as well as the individual components. You will also need the chemical formulas and percent compositions of chloride for NaCl and KCl. Additionally, you will need a container or beaker to hold the mixture and any necessary lab equipment for handling and separating the mixture.

4. What are the possible sources of error when determining the mass percent of chloride from a mixture of NaCl and KCl salts?

There are several potential sources of error when determining the mass percent of chloride from a mixture of NaCl and KCl salts. These include inaccurate measurements of the mass of the mixture and individual components, incomplete separation of the mixture into its components, and errors in the chemical formulas or percent compositions of chloride for NaCl and KCl. It is important to carefully follow the procedure and double-check all measurements and calculations to minimize these errors.

5. Can the mass percent of chloride be determined for mixtures of other salts?

Yes, the mass percent of chloride can be determined for mixtures of other salts using the same method described for NaCl and KCl. However, the percent compositions of chloride for each salt will need to be known in order to accurately calculate the mass percent. It is also important to consider any potential reactions or interactions between the salts in the mixture, which may affect the accuracy of the results.

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