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Mass of zinc = 1.050 g. Calculate the number of moles of zinc in the 250 mL flask (show workings) Calculate the concentration zinc in the 250 mL flask (show workings) Calculate the number of moles of Zn2+ in the 20 mL aliquot (show workings)

Mass of zinc = 1.050 g. Calculate the number of moles of zinc in the 250 mL flask (show workings) Calculate the concentration zinc in the 250 mL flask (show workings) Calculate the number of moles of Zn2+ in the 20 mL aliquot (show workings)

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
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Standardisation of EDTA using zinc metal                                                

Mass of zinc = 1.050 g.

  1. Calculate the number of moles of zinc in the 250 mL flask (show workings)
  2. Calculate the concentration zinc in the 250 mL flask (show workings)
  3. Calculate the number of moles of Zn2+ in the 20 mL aliquot (show workings)
  4. Calculate the number of moles of EDTA in the average titre (show workings)
  5. Calculate the concentration of the DILUTED EDTA solution (show workings)

Sample No.

1

2

3

4

Final Burette reading

(mL)

 

20.25

42.75

22.90

44.50

Initial Burette reading

(mL)

0.05

20.25

1.50

22.90

Final-Initial Titre (mL)

20.20

22.50

21.40

21.60
PROCEDURE: 1. In a weighing bottle, weigh out accurately on the analytical balance 0.9 - 1.1 g of the zinc metal provided. 2. Transfer the metal carefully to a 50 ml conical flask and in the fume hood, carefully add ~4 ml of concentrated HCI into the flask to dissolve the metal 3. Cool the solution and add concentrated NaOH drop-wise until a permanent faint white precipitate forms. 4. Add 5 M HCl drop-wise to neutralize the solution until the zinc hydroxide (Zn(OH)₂) precipitate just dissolves. Add a further 5 drops more of the acid to acidify the solution. Transfer the solution carefully to a 250 ml volumetric flask and make up to the mark with distilled water. Stopper the flask firmly and shake it to ensure a homogeneous solution. Using a buretta deliver exactly 20.00 ml of the standard zinc solution into a clean 5. 6. 250 ml conical flask. Add 70 ml of distilled water and 10 ml of the buffer solution (pH = 10). Then add four (4) drops of the indicator solution Repeat step (6) a further 3 times so that you have a total of four conical flasks of solution for consecutive titrations. 7. 8. Titrate with the EDTA solution until the end-point is reached (WINE-RED to PURE BLUE). 9. Repeat the titration until three (3) concordant results are obtained. Part B. Determination of Water Hardness (Total Ca²+ and Mg²+ Content) Table 1 Classification of water harness with respect to the concentration od calcium carbonate in water mg/L or ppm Classification Soft Moderately Hard Hard Very Hard 0-60 61-120 121-180 > 180 PROCEDURE: 1. Dilute the EDTA solution by dispensing 25.0 ml of the given EDTA from a burette into a 250 ml volumetric flask and make up to the mark with distilled water. 2. Rinse and fill the burette with the diluted EDTA solution. 3. Dispense a 20 ml aliquot of the hard water sample into a 250 ml conical flask. Add 2 ml of buffer solution (pH 10). Add 4 drops of the Eriochrome black T indicator solution. 4. Repeat step (3) a further 3 times so that your have four conical flasks of the water solution for the repeat titrations. 5. Titrate the water sample with the EDTA solution until the colour changes from wine-red to pure blue. 6. Repeat the titration until three (3) concordant results are obtained. 7. Express the water hardness in mol L-1 of (Ca²+ + Mg²+). 8. Assuming the water hardness is only due to the presence of Ca²+, express the water hardness in terms of mg L-1 of CaCO3.
Transcribed Image Text:PROCEDURE: 1. In a weighing bottle, weigh out accurately on the analytical balance 0.9 - 1.1 g of the zinc metal provided. 2. Transfer the metal carefully to a 50 ml conical flask and in the fume hood, carefully add ~4 ml of concentrated HCI into the flask to dissolve the metal 3. Cool the solution and add concentrated NaOH drop-wise until a permanent faint white precipitate forms. 4. Add 5 M HCl drop-wise to neutralize the solution until the zinc hydroxide (Zn(OH)₂) precipitate just dissolves. Add a further 5 drops more of the acid to acidify the solution. Transfer the solution carefully to a 250 ml volumetric flask and make up to the mark with distilled water. Stopper the flask firmly and shake it to ensure a homogeneous solution. Using a buretta deliver exactly 20.00 ml of the standard zinc solution into a clean 5. 6. 250 ml conical flask. Add 70 ml of distilled water and 10 ml of the buffer solution (pH = 10). Then add four (4) drops of the indicator solution Repeat step (6) a further 3 times so that you have a total of four conical flasks of solution for consecutive titrations. 7. 8. Titrate with the EDTA solution until the end-point is reached (WINE-RED to PURE BLUE). 9. Repeat the titration until three (3) concordant results are obtained. Part B. Determination of Water Hardness (Total Ca²+ and Mg²+ Content) Table 1 Classification of water harness with respect to the concentration od calcium carbonate in water mg/L or ppm Classification Soft Moderately Hard Hard Very Hard 0-60 61-120 121-180 > 180 PROCEDURE: 1. Dilute the EDTA solution by dispensing 25.0 ml of the given EDTA from a burette into a 250 ml volumetric flask and make up to the mark with distilled water. 2. Rinse and fill the burette with the diluted EDTA solution. 3. Dispense a 20 ml aliquot of the hard water sample into a 250 ml conical flask. Add 2 ml of buffer solution (pH 10). Add 4 drops of the Eriochrome black T indicator solution. 4. Repeat step (3) a further 3 times so that your have four conical flasks of the water solution for the repeat titrations. 5. Titrate the water sample with the EDTA solution until the colour changes from wine-red to pure blue. 6. Repeat the titration until three (3) concordant results are obtained. 7. Express the water hardness in mol L-1 of (Ca²+ + Mg²+). 8. Assuming the water hardness is only due to the presence of Ca²+, express the water hardness in terms of mg L-1 of CaCO3.
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