1) calculate the concentration of H2SO4 for the initial solution from your resul
ID: 497534 • Letter: 1
Question
1) calculate the concentration of H2SO4 for the initial solution from your results for part B and C. which result, B andor C, is likely to be precise. explain?
2) There is an inherent flaw in the drying procedure for the gravimetric determination that causes the measured mass of BaSO4 to be erroneously high. what is it and how could the procedure be improved?
3) If the volumetric procedure yields more accurate, why perform the gravimetric procedure at all?
4) If the BaSO4 reside was baked in an oven at 100 C for several hours rather than air drying, what effect would this have on its mass and how would the initial concentration of H2SO4 be affected (higher, lower, or no change)? explain.
5) if a 20 mL pipet was unknowingly used in pipetting the final solution in part C, How would the calculated initial concentration of H2SO4 be affected (higher, lower, or no change)? Explain.
Part B: Gravimetric Determination of Sulfate Ion
Part B
Trial 1
Trial 2
Trial 3
Trial 4
Mass of BaSO4, and filter paper, g
1.1434
Mass of filter paper,g
0.9819
Mass of BaSO4 precipitate, g
0.1615
0.4402
0.3028
0.676
Millimoles of BaSO4
0.2
0.2
0.2
0.2
Millimoles of H2SO4 that reacted
Volume of the final solution, mL
5
5
5
5
[H2SO4], final solution, M
0.15
[H2SO4], stock solution, M*
0.6
[H2SO4], initial solution, M*
Average [H2SO4], initial solution, M
Part C: Volumetric Determination of Acid Concentration
Molarity of NaOH(aq)
Part C
Trial 1
Trial 2
Trial 3
Trial 4
Initial NaOH buret reading, mL
50
Final buret reading, mL
19.3
Volume of NaOH(aq) used, mL
30.7
24
35.1
124.4
Millimoles of NaOH
Millimoles of H2SO4 titrated
Volume of final solution titrated, mL
10
10
10
10
[H2SO4], final solution, M
[H2SO4], stock solution, M*
[H2SO4], initial soln, M*
Average [H2SO4], initial soln, M
Part B
Trial 1
Trial 2
Trial 3
Trial 4
Mass of BaSO4, and filter paper, g
1.1434
Mass of filter paper,g
0.9819
Mass of BaSO4 precipitate, g
0.1615
0.4402
0.3028
0.676
Millimoles of BaSO4
0.2
0.2
0.2
0.2
Millimoles of H2SO4 that reacted
Volume of the final solution, mL
5
5
5
5
[H2SO4], final solution, M
0.15
[H2SO4], stock solution, M*
0.6
[H2SO4], initial solution, M*
Average [H2SO4], initial solution, M
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1. Calculations
B. Determination of sulfate ion and H2SO4 molarity by gravimetry
BaSO4 ppt (g) : 0.4698 g
BaSO4 (mmol) : 0.4698/233.38 = 2.0
H2SO4 (mmol) : 2.0
Initial volume (ml) : 5 ml
H2SO4 (M) : 2.0 mmol/5 ml = 0.4 M
C. Volumetric determination of H2SO4 concentration
NaOH (M) : 0.1 M
NaOH (ml) used : 35.1
NaOH (mmol) : 0.1 x 35.1 = 3.51
H2SO4 (mmol) : 3.51/2 = 1.755
Initial volume (ml) : 10 ml
H2SO4 (M) : 1.755 mmol/10 ml = 0.1755 M
The more accurate would be the gravimetric analysis for the determination of H2SO4 molarity. The gravimetric analysis takes care of removing all the impurities and experimental error usually found in titration methods.
2. The inherent flow in the drying procedure for the gravimetric analysis of BaSO4 results into higher mass of the precipitate as it does not remove any water of crystallization from the precipitate formed.
3. The volumetric method If gives a accurate result, we still need to carry out gravimetric analysis to fully confirm the results of the volumetric analysis in the determination of molarity of H2SO4.
4. If the precipitate of BaSO4 was dried at 100 oC instead of air drying, the mass of precipitate found would be lower than the previous calculated precipitate mass as the higher temperature tends to remove any water or moisture stuck between the crystals.
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