Question

The following data were collected from the gravimetric analysis of a hydrated salt: Complete the following table. (See Report Sheet.) See Data Analysis C, D for determining the standard deviation and relative standard deviation for a set of data. Express all of the calculated data with the correct number of significant figures (see Data Analysis A). Mass of hydrated salt(g) Mass of anhydrous salt(g) Mass of water lost(g) Percent by mass of volatile water in hydrated salt(%) Average percent H_2O in hydrated salt(%H_2O) Standard deviation of % H_2O Relative standard deviation of %H_2O in hydrated salt (%RSD)

Answer 1

Mass of hydrated salt can be found as

Mass of fired crucible, lid and hydrated salt - Mass of fired crucible & lid

Mass of hydrated salt for all the trials is calculated below

Trial 1 ------ 21.626 g - 19.437 g = 2.189 g

Trial 2 ------ 25.111 g - 20.687 g = 4.424 g

Trial 3 ------- 22.167 g - 18.431 g = 3.736 g

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Mass of anhydrous salt is calculated as

Mass of fired crucible, lid and anhydrous salt - Mass of fired crucible & lid

Mass of anhydrous salt for all the trials is calculated below

Trial 1 ----------- 21.441 g - 19.437 g = 2.004 g

Trial 2 ---------- 24.702 g - 20.687 g = 4.015 g

Trial 3 --------- 21.762 g - 18.431 g = 3.331 g

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Mass of water lost is calculated as

Mass of hydrated compound - Mass of anhydrous compound

Mass of water lost for all the trials is calculated below

Trial 1 ------- 2.189 g - 2.004 g = 0.185 g

Trial 2 -------   4.424 g - 4.015 g = 0.409 g

Trial 3 -------   3.736 g - 3.331 g = 0.405 g

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Percent by mass of volatile water in hydrated compound is calculated as

Mass of water lost / Mass of hydrated compound * 100

Percent by mass of volatile water for all the trials is given below

Trial 1 ---------- 0.185 g / 2.189 g * 100 = 8.45%

Trial 2 -------- 0.409 g / 4.424 g * 100 = 9.26%

Trial 3 ---------- 0.405g / 3.736 g * 100 = 10.84 %

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Average % H2O = 8.45 + 9.26 + 10.84 / 3 = 9.52 %

Average percent H2O in hydrated salt is 9.52%

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Standard deviation is calculated as follows

Mass of hydrated salt can be found as Mass of fired crucible, lid and hydrated salt - Mass of fired crucible & lid Mass of hydrated salt for all the trials is calculated below Trial 1 21.626 g - 19.437 g = 2.189 g Trial 2 25.111 g - 20.687 g = 4.424 g Trial 3 22.167 g - 18.431 g = 3.736 g Mass of anhydrous salt is calculated as Mass of fired crucible, lid and anhydrous salt Mass of fired crucible & lid Mass of anhydrous salt for all the trials is calculated below Trial 1 21.441 g - 19.437 g = 2.004 g Trial 2 24.702 g - 20.687 g = 4.015 g - Trial 3 21.762 g - 18.431 g = 3.331 g Mass of water lost is calculated as Mass of hydrated compound - Mass of anhydrous compound Mass of water lost for all the trials is calculated below Trial 1 2.189 g - 2.004 g = 0.185 g

Let us make a table to find (x- average x ) values

Trial	x ( % of water)	(x - average x)	( x - average x)^2
1	8.45	8.45 - 9.52 = -1.07	(-1.07)^2 = 1.1449
2	9.26	9.26 - 9.52 = -0.26	(-0.26)^2 = 0.0676
3	10.84	10.24 - 9.52 = 0.72	(0.72)^2 = 0.5184

Total ( x - average x)^2 = 1.1449 + 0.0676 + 0.5184 = 1.7309

n = number of trials, = 3

Substituting above values in S.D formula, we get

S.D . = Sq rt ( 1.7309 / 3-1)

S.D = Sq rt ( 0.8655)

S.D = 0.9303

Standard deviation of % of H2O is 0.9303

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Relative standard deviation is calculated as

% RSD = Standard deviation / Mean( average of % H2O) * 100

% RSD = 0.9303 / 9.52 * 100

% RSD = 9.772 %