top-rated free essay


By ZachWats Nov 14, 2013 1141 Words


Report By: ____________
Lab Partner: ___________
Group: CHEM 1001 Tuesday AM, Group H

This lab was conducted in order to determine the content of chloride in an unknown salt, using gravimetric analysis.

The salt chloride content is easy to find because it is slightly soluble, making it possible to turn it into a precipitate. A precipitate reaction can be done using silver to isolate the specific ion.

Ag+(aq) + Cl-(aq) --> AgCl(s)

Despite AgCl(s) being highly insoluble, some of the substance will still dissolve. This dissolved portion can be calculated.

AgCl(s) => Ag+(aq) + Cl-(aq) Ksp = [Ag+(aq)]·[Cl-(aq)] = 1.6 x 10-10

Since Ksp is so small the dissolved are to be considered negligible. Both ions will precipitate out very quickly to AgCl when the AgNO3 is added to the solution with the Cl- ions until all of these ions are consumed. Small amounts of salt will still remain in the solution because the maximum solubility to be reached when there is no longer excess Ag+. The remaining Cl- can be calculated still.

With no excess Ag+, [Ag+] = [Cl-]; let both = x

Ksp = [Ag+(aq)]∙[Cl-(aq)] = 1.6 x 10-10
[x]∙[x]=1.6 x 10-10
x =1.3 x 10-5

Due to the speed of formation, it precipitates as a colloid, and the particles remain very small due to the lack of time to crystallize. The colloid must be heated in an acid media to form larger, crystalline pieces so it can be poured into the crucible without passing through the filter. The acid media also prevents the new crystalline pieces from going back to a colloid state. Another cause of the fast reaction is the trapping of other ions. The acid media also resists any interference of any anions, such as CO3 2-, that may be able to for precipitate with silver ions.

Photodecomposition can occur in the precipitate (AgCl(s) => Ag(s) + (1/2)Cl2(g)). This reaction mainly occurs on the surface of the precipitate because it is most exposed to light, making the effects not too high. With significant excess Ag+, the decomposition can lead to CIO3 being formed (3Cl2(g) + 9H20(l) + 5Ag+(aq) => 5AgCl(s) + CIO3-(aq) + 6H3O+(aq)).

The amount of precipitate lost during the 100 mL distilled water rince can be calculated using the Ksp value.

n=Ksp x 0.1 L
n= 1.6 x 10^-11 mols

m= (1.6 x 10^-11 mol)(143.32 g/mol)
m= 2.3 x 10^-9 g Therefor a maximum of 2.3x10^-9 g can be lost during the rinse.


All of the following procedures where carried out individually by both laboratory partners. The unknown salt sample was obtained and its number recorded. An analytical balance was used to weigh out by difference a sample of the salt weighing just over 0.1000g and the sample was then placed in a numbered 250mL beaker. The volume of 0.1 M AgNO3 needed for the precipitation was calculated between waiting times for the analytical balance. 100 ML of distilled water and 1 mL of dilute HNO3 was then added to the beaker with the salt sample and stirred. The necessary quantity of AgNO3 was slowly added to the beaker as well while stirring the contents of the beaker. The beaker was then placed onto a hot plate to heat up, and was heated and gently stirred until the contents became fairly translucent in comparison to its original state. Drops of silver nitrate were added to check for completeness. The beaker was then placed into a drawer, out of any light source, to cool. The crucible was labeled and weighed in the analytical balance. The crucible was then used to set up a vacuum filtration apparatus, and the liquid in the beaker was poured through the crucible while the precipitate remained in the beaker. 0.01 M HNO3 was added to the beaker and the beaker was gently swirled to wash the precipitate. The washings were then poured through the crucible and the precipitate remained in the beaker. The same HNO3 wash was conducted again, except both the washings and the precipitate were poured onto the filter. More of the HNO3 was poured over the precipitate to wash it. After the removal of the crucible, the flask in the vacuum collection was cleaned and set back up with the crucible. Another wash of the precipitate was done with the HNO3, and the new washings in the flask were transferred into a test tube for a TA to test for turbidity. Once this test passed, the precipitate was washed with three 5 mL portions of acetone using the filtration system. The crucible was dried by placing it into an oven for about half of an hour. After drying the crucibles were cooled then weighed using the analytical balance.


Sample #360

Precipitation Completion Test
Completeness of Washing Test
Precipitate Description
White, fine granular powder.
Precipitate was a purple/white powdered substance
Partners Sample
White, fine granular powder.
Precipitate was a purple/white powdered substance


Partners Values
Weight of Sample
0.1313 g (+/- 0.0001 g)
0.1484 g (+/- 0.0001 g)
Weight of Precipitate
0.2746 g (+/- 0.0002 g)
0.3134 g (+/- 0.0002 g)
Volume of AgNO3
20.3 mL
27.99 mL
Oven Temperature
108 C (+/- 0.2 C)
108 C (+/- 0.2 C)
Drying Time
28 min
28 min
Cooling Time
5 min
5 min
Actual % of Cl


Sample 1
Partners Sample
n= (0.2746 g) / (107.8682+35.453)g/mol
n= 0.0019 mol

m= 0.0019 mol x 35.435 g/mol
m= 0.0674 g

%m= (0.0674 g/ 0.1313 g) x 100%
%m= 51.33%

error= ((51.33%-53.35%)/(53.35%))x100
error= -3.79%
n= (0.3134 g) / (107.8682+35.453)g/mol
n= 0.0022 mol

m= 0.0019 mol x 35.435 g/mol
m= 0.0780 g

%m= (0.0674 g/ 0.1313 g) x 100%
%m= 52.56%

error= ((52.56%-53.35%)/(53.35%))x100
error= -1.48%

Avg= (51.33%+52.56%)/(2)
Avg= 51.95%

Rel. Spread= ((52.56%-51.33%)/(51.95%))x1000 ppt
Rel. Spread= 23.7 ppt

This experiment proved to be very accurate. Looking at the relative error for both samples, the value is very small. This information proves the use of proper laboratory techniques were prominent and the procedure was followed carefully. The results were not perfect, do to uncertainties and human error. Both percent values were lower than the actual value. A reason for this is the silver chloride decomposing back to its ions due to the exposure of light to the precipitate. When this exposure of light occurs the precipitate appears to turn violet, which both precipitates did. The decomposition in light plays a huge factor in a lower yield. Other reasons could be inaccurate use of the analytical balance, leaving small remnants of the precipitate in the beaker and also small amounts of precipitate may have passed through the crucible.

The salt sample #360 was calculated to have an average value of 51.95% Cl, when compared to the actual value of 53.35% is very similar. The accuracy of this experiment was excellent with errors of -3.79% and -1.48%, and a decent precision with a relative spread of 23.7 ppt.


Burk, R. C., Azad, M., Sun, X., & Wolff, P. A. (2013). Introduction chemistry laboratory manual. (CHEM 1001/1002 ed., pp. 57-59). Ottawa: Carleton University.

Cite This Document

Related Documents

  • The Gravimetric Analysis of Chloride Salt

    ...Gravimetric Analysis of a Chloride Salt CHEM 1001 Purpose: To illustrate typical techniques used in gravimetric analysis by determining quantitatively the chloride content in an unknown soluble salt. Theory: AgCl(s) is a very insoluble solid, yet still does have some solubility. Because of these traits, the following reaction is abl...

    Read More
  • Gravimeter Analysis Of A Chloride Salt

    ...Gravimeter Analysis of a Chloride Salt Author Name: Abdulla Almahmood Partner: Mohamed Almahmood Date: November 11, 2014 Group: A4 PURPOSE To find the amount of chloride in an unknown salt using typical techniques of gravimetric analysis. THEORY Adding Silver Ion In Order To Precipitate Chloride Ion Due to the extreme insolubility of...

    Read More
  • Gravimetric analysis of a salt

    ...techniques and procedures used to gravimetric labs. For this particular lab we will utilize our scientific knowledge of related to gravimetric procedures to find the chloride content in an unknown soluble salt. Theory: Using our developed knowledge of the conservation of mass, solubility and precipitation it is possible (with some degree of e...

    Read More
  • Gravimetric Analysis

    ...GRAVIMETRIC ANALYSIS Methods in GA Precipitation Method - involves isolation of an ion in solution by a precipitation reaction, filtering, washing the precipitate free of contaminants, conversion of the precipitate to a product of known composition, and finally weighing the precipitate and determining its mass by difference. From the mass and...

    Read More
  • Gravimetric Analysis

    ...Gravimetric Analysis CHEM 200-03 Fall Semester 2012 September 19, 2012 Jeff Marasigan Abstract Gravimetric analysis is based on the quantitative isolation of the desired constituent the analyte of interest from the sample in highly pure form or in some combined form and weighing the isolated constituent. The desired constituent ...

    Read More
  • Gravimetric Analysis

    ...Gravimetric Analysis Report Aim: Determine the % by mass composition of a sand-salt mixture. Background: Gravimetric analysis is a method which is based on the isolation of the desired sample in pure forms or in some combined form from a sample, and weighing the isolated constituent. Then from the weights of the sample or precipitate, a perce...

    Read More
  • Gravimetric Analysis

    ...Gravimetric Analysis of SULFATE as Barium Sulfate. Objectives * To learn the techniques associated with gravimetric analysis. * To use stoichiometry to calculate the percentage by mass of sulfate in an unknown sulfate salt. Background Gravimetric analysis is a quantitative method for accurately determining the amount of a substance...

    Read More
  • Gravimetric Analysis

    ...Gravimetric analysis, by definition, includes all methods of analysis in which the final stage of the analysis involves weighing. In the most basic case, this could involve simply heating a sample to dryness and weighing to determine the amount of volatile components. In this account, however, shall limit to gravimetric methods which rely on the...

    Read More

Discover the Best Free Essays on StudyMode

Conquer writer's block once and for all.

High Quality Essays

Our library contains thousands of carefully selected free research papers and essays.

Popular Topics

No matter the topic you're researching, chances are we have it covered.