A sample of a CACl_2 2H_2O/K_2C_2O_4 H_2O solid salt mixture is dissolved in -15

Question

A sample of a CACl_2 2H_2O/K_2C_2O_4 H_2O solid salt mixture is dissolved in -15 mL of deionized water adjusted to a pH that is basic. The precipitate, after having been filtered, was air-dried and weighed. Date for were obtained as shown. Complete the following table. Record calculate values with the number of significant figures. For Trials 2 and 3, the percent CaCl_2 2H_2O in the mixture was 39.7% and 28.4% respectively. What is the average percent of Cacl_2 2H_2O in the sample? Date Analysis, B. What are the standard deviation and the relative standard deviation (%RSD) for the percent of CaCl_2 2H_2O is the sample? Date Analysis, C and D.

Explanation / Answer

B. 2. Excess reactant in salt mixture = K2C2O4. H2O

Data Analysis:

1. Moles of CaC2O4.H2O precipitated = Weight of CaC2O4.H2O / Molecular weight = 0.284 g / 146.1123 g/mol = 0.0019 mol

2. Moles of limiting reagent in mixture = Moles of CaC2O4.H2O precipitated = 0.0019 mol

3. Mass of limiting reagent in salt mixture = Moles of limiting reagent x Molecular weight = 0.0019 mol x 147.0 g/mol = 0.279 g

4. Mass of excess reagent in salt mixture = Mass of Salt mixture - Mass of limiting reagent = 0.879 - 0.279 = 0.6 g

5. Percent limiting reagent in salt mixture = (Weight ot limiting reagent x 100) / Weight of salt mixture = (0.279 x 100) / 0.879 = 31.74 %

6. Percentage excess reagent in salt mixture = 100 - 31.74 = 68.26 %

a. Average percentage = (39.7 + 28.4) / 2 = 34.05 %

b. Standard deviation = [(39.7 - 34.05)2 + (28.4 - 34.05)2] / 2 = (31.9225 + 31.9225) / 2 = 31.9225

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