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The following data were collected from the gravimetric analysis of a hydrated salt:
Trial 1 Trial 2 Trial 3
1. Mass of fired crucible and lid (g) 19.437 20.687 18.431
2. Mass of fired crucible, lid, and 21.626 25.111 22.167
hydrated salt (g)
3. Final mass of fired crucible, lid 21.441 24.702 21.762 and anhydrous salt (g)
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).
Calculations
Trial 1 Trial 2 Trial 3
1. Mass of hydrated salt (g)
2. Mass of anhydrous salt (g)
3. Mass of water lost (g)
4. Percent by mass of volatile water
in hydrated salt (%)
5. Average percent H2O in hydrated Data Analysis,B
salt (%H2O)
♦ Relevant knowledge
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The Gravimetric Analysis is a tests performed in laboratories and techniques that are designed to determine the quantity of an analytical substance (substance that is quantified) in a particular sample. This is done by determining the composition by mass of the specimen using specific instruments and methods.
You can find hydrated salt mass as:
Mass of fired crucible, lid and hydrated salt – Mass of fired crucible & lid
Below is the calculated mass of hydrated salt used in all trials
Trial 1 —— 21.626g – 19.437g = 2.189 g
Trial 2 —— 25.111g – 20.687g = 4.424 g
Trial 3 ——- 22.167g – 18.431g = 3.736 g
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The mass of anhydrous salt can be calculated as
Mass of fired crucible, lid and anhydrous salt – Mass of fired crucible & lid
Below is the calculated mass of anhydrous salt used in all trials
Trial 1 ———– 21.441g – 19.437g = 2.004 g
Trial 2 ———- 24.702g – 20.687g = 4.015 g
Trial 3 ——— 21.762g – 18.431g = 3.331 g
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Calculation of the water loss in mass
Mass of hydrated compound – Mass of anhydrous compound
Below is the calculation of the water loss for each trial
Trial 1 ——- 2.189g – 2.004g = 0.185 g
Trial 2 ——- 4.424g – 4.015g = 0.409 g
Trial 3 ——- 3.736g – 3.3331g = 0.405 g
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Calculated as: Percentage by mass of volatile water within hydrated compound
Mass of water lost / Mass of hydrated compound × 100
Below is the percentage of volatile water in all trials.
Trial 1 ———- 0.185g / 2.189g × 100 = 8.45%
Trial 2 ——– 0.404 g / 4.24 g × 100 = $1strongTag26$
Trial 3 ———- 0.404g / 3.7336 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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The standard deviation is calculated as follows
Let’s make a table and find the (x-average x ) values
Total ( x – average x)2 = 1.1449 + 0.0676 + 0.5184 = 1.7309
n = Number of Trials, = 3
We get the following results by substituting the above values into the S.D formula
S.D . = √( 1.7309 / 3-1)
S.D = √( 0.8655)
S.D = 0.9303
Standard deviation of % of H2O is 0.9303
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The relative standard deviation is calculated using the following formula
% RSD = Standard deviation/Mean (average of % H2O)×100
% RSD = 0.93303 / 9.52 × 100
% RSD = 9.772 %