Data and Calculations: Analysis of an Unknown Chloride Molarity of standard AgNO
ID: 557691 • Letter: D
Question
Data and Calculations: Analysis of an Unknown Chloride Molarity of standard AgNO, solution O l044 M Initial buret reading 1& go Final buret reading 18 go Volume of AgNO3 used to titrate sample mL Moles of AgNO3 used to titrate sample 3 771 Xlo Moles of Cl present in sample 3.37710 Y lo Volume of diluted chloride solution pipetted mL 00 mL 10.0 mL Total moles of Cl in 100 mL vol flask 2-7741 3x3-135x1 Cl concentration in diluted solution in volumetric flask 2 374xle M331 3135 1ieM Mean chloride concentration Standard deviation in chloride concentration Unknown #Explanation / Answer
% error for the calculated Cl- concentration values:
Mean Cl- concentration (Obtained experimental value) =
= (3.779*10-2 + 3.377*10-2 + 3.135*10-2) / 3 = = 3.4303 *10-2 M = 0.0343 M
Given (theoretical) Value of Mean Cl- concentration = 0.025 M
So the value of mean Cl- concentration should have been 0.025 M but what we obtaind is 0.0343 M. The difference of these values wrt to the given value is "percent error".
% Error = [(0.0343 M - 0.025 M)/ 0.025 M ] * 100 = 0.0093*100 / 0.025 = 37.2%
% Error simply tells you the magnitude of the mistakes happened during the experiment or how far the experiment .A low % error means experiment was effective however a high % error means experiment was ineffective.
The reason for having the % error in can be understood from the combined mistakes during an experiment like non calibration of equipments, contamination in reagents, inaccuracy of sample preparation etc.
These things differ from experiment to experiment and not remain same always, thats why we have different-2 results givening rise to the error of the expected given value.
Now, were all your trials high? low? some of each?
The value of % error wrt the given value for experiment I, II, III :
For experiment I: % Error = [(0.0377 M - 0.025 M)/ 0.025 M ] * 100 = 50.8%
For experiment II: % Error = [(0.0337 M - 0.025 M)/ 0.025 M ] * 100 = 34.8%
for experiment III % Error = [(0.0313 M - 0.025 M)/ 0.025 M ] * 100 = 25.2%
In general, If % error is less than 5%, your value can be accepted as reliable.
So all the trials are very quite high wrt to the given value.
Std. deviation for the calculated Cl- concentration values:
Values obtained are 0.03779, 0.03377, and 0.03135.
Std deviation for calculated values = 0.00325
Std deviation given = 253 * 10-2 = 0.0253
An experiment that yields data with a low standard deviation is said to have high precision.
Standard deviation provides a way to check the results. Very large values of standard deviation can mean the experiment is faulty.
The lower value of "Std deviation for calculated value" as compare to "Std deviation for given value" shows that the experiments are more precise.
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