Gravimetric Analysis: Calculating % NaCl in Impure Sample

  • Thread starter Jason03
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In summary, the problem involves finding the percentage of NaCl in an impure sample of table salt by dissolving it in water and treating it with excess AgNO3. The impurities in the sample are assumed to be insoluble and the precipitate formed is weighed to determine the amount of AgCl. The reaction involved is the formation of AgCl from AgNO3 and NaCl. By using the molar ratio between AgCl and NaCl, the percentage of NaCl in the impure sample can be calculated.
  • #1
Jason03
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Im working on the below problem

An impure sample of table salt that weighed .8421 g, when dissoved in water and treated with exess AgNO3, formed 2.044g of AgCL. What is the percentage of NaCl in the impure sample..

Im trying to figure the approach to this problem...Any ideas?
 
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  • #2
Sodium Chloride is dissolved in water. What does that mean?
Silver Nitrate is added and insoluble Silver Chloride is isolated and weighed.

What is the reaction? You just work backward to find amount of sodium chloride in the original "impure" sample. What is the expected impurity? How do you know that some other chloride compound is not also present?
 
  • #3
NaCl dissolved in water means that the salt will completely disolve into the water...the impurities wouldn't dissolve...Silver Nitrate added to water forms a precipitate...hence the Silver Chloride...But what about the sodium?

Im just not sure how to start...
 
  • #4
Quoting from original poster Jason03:

...the impurities wouldn't dissolve...

How do you know that they would or would not dissolve? What are the impurities? Do you need to assume anything about them?

hence the Silver Chloride

Where is the written reaction which forms Silver Nitrate? Write it and use it.

You also asked about Sodium. What form of it is present in the solution? What do you know about solubility of sodium compounds?
 
  • #5
This would be the reaction


AgNO3 + NaCl ----------------> AgCl + NaNO3
 
Last edited:
  • #6
Ok I think I got it...

From the reaction we know that 1 mole of AgCl is is equal to 1 mole of NaCl

so ...2.044g of AgCl/(143.33g/mole) = 0.01426 moles of AgCl...

than...(0.01426)(58.44g/mole) = .8334g NaCl

so... .8334/.8421 = 98.79%
 
  • #7
Jason03,
Your work appears good. I did not check your numeric values, but your units are well handled. Your logical steps seem good.
 
  • #8
Thanks for the Help!
 

What is gravimetric analysis?

Gravimetric analysis is a quantitative analytical method used to determine the amount of a specific substance in a sample by measuring its mass.

How is % NaCl calculated in an impure sample using gravimetric analysis?

In gravimetric analysis, the % NaCl is calculated by measuring the mass of the sample before and after the precipitation of NaCl. The difference in mass is used to determine the amount of NaCl present in the sample and the % NaCl is calculated by dividing the mass of NaCl by the total mass of the sample and multiplying by 100.

What are the steps involved in gravimetric analysis for calculating % NaCl in an impure sample?

The steps involved in gravimetric analysis for calculating % NaCl in an impure sample include: 1. Collecting a representative sample of the impure substance 2. Dissolving the sample in water 3. Adding a known amount of a precipitating agent 4. Filtering the solution to separate the precipitate 5. Drying and weighing the precipitate 6. Calculating the % NaCl in the sample based on the mass of the precipitate and the original sample.

What are the potential sources of error in gravimetric analysis for calculating % NaCl in an impure sample?

Potential sources of error in gravimetric analysis include: 1. Contamination of the sample during collection or handling 2. Incomplete precipitation of the substance 3. Loss of precipitate during filtering or drying 4. Inaccurate measurements of mass 5. Presence of other substances that may interfere with the precipitation process.

What are the advantages of using gravimetric analysis for calculating % NaCl in an impure sample?

The advantages of gravimetric analysis include: 1. High precision and accuracy 2. Can be used to analyze a wide range of substances 3. Does not require expensive equipment 4. Can be performed on small sample sizes 5. Results are not affected by the presence of other substances in the sample.

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