Gravimetric Analysis: Calculating % NaCl in Impure Sample

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Discussion Overview

The discussion revolves around a gravimetric analysis problem involving the calculation of the percentage of sodium chloride (NaCl) in an impure sample of table salt. Participants explore the chemical reactions involved, the assumptions regarding impurities, and the steps necessary to arrive at a solution.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • The original poster seeks guidance on how to approach the problem of calculating the percentage of NaCl in an impure sample after treatment with silver nitrate (AgNO3).
  • Some participants discuss the dissolution of NaCl in water and the implications for impurities, questioning what those impurities might be and whether they dissolve.
  • There is a focus on the chemical reaction between AgNO3 and NaCl, with a participant providing the balanced equation for the reaction.
  • One participant calculates the moles of AgCl formed and subsequently determines the mass of NaCl, leading to a percentage calculation.
  • Another participant questions the assumptions made about the solubility of impurities and the form of sodium present in the solution.

Areas of Agreement / Disagreement

Participants express varying levels of certainty regarding the assumptions about impurities and their solubility. There is no consensus on the nature of the impurities or their impact on the calculation.

Contextual Notes

Participants highlight the need for assumptions regarding the impurities present in the sample and their solubility, which remain unresolved. The discussion also notes the importance of correctly identifying the chemical reactions involved.

Who May Find This Useful

This discussion may be useful for students and educators involved in chemistry, particularly those studying gravimetric analysis and the principles of solubility and chemical reactions.

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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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?
 
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...
 
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?
 
This would be the reaction


AgNO3 + NaCl ----------------> AgCl + NaNO3
 
Last edited:
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%
 
Jason03,
Your work appears good. I did not check your numeric values, but your units are well handled. Your logical steps seem good.
 
Thanks for the Help!
 

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