Question

 

Assay for Al3+

Pipette 25.00 mL of the prepared sample into a 250 mL conical flask and add 20 mL of water. Then, with swirling add, by pipette, 25.00 mL of 0.01 mol L-1 EDTA (you need to copy down the EXACT concentration (it therefore should not have just one or two significant figures!) of EDTA provided). Continue stirring, and add 20 mL of pH 4.5 buffer. (NOTE: The order of these additions is important). Heat the solution in a microwave oven for 2 minutes. Cool, add 50 mL ethanol and then 2 mL of dithizone indicator (be careful not to use any undissolved dithiozone).

1. Titrate with 0.01 mol L-1 zinc sulfate standard (copy down the EXACT concentration) until the colour changes from green-violet to rose-pink. You should estimate the titre to 2 decimal places. 2. Perform a blank, using 25.00 mL of deionised water instead of the prepared sample. 3. Repeat the titration to obtain three concordant values.

Al3+ titration
V1/ mL	V2/ mL	V2-V1/ mL		mean V
0	22.1	22.1		21.6
22.1	43.5	21.4		SDv
14.65	35.95	21.3		0.43589
back titration/blank
V1/ mL	V2/ mL	V2-V1/ mL
0.1	24.55	24.54

antacid powder weight:0.6499g

EDTA concL 0.0098 mol/L

zinc sulfate conc: 0.0100 mol/L

Answer 1

Its incorrect the way you calculated.

It must be prepared three or more probem's solution of Al³⁺ by the same protocol. Each solution must be titrated with ZnSO₄ standard solution. It must be annotated each pippete volume with two decimals. It must be prepared at least three blank solution which must be titrated with ZnSO₄ standard solution. It must be annotated each pippete volume with two decimals. Blank results is the average of replicable values. Solution results is the average of replicable values. Finally, aluminium(III) concentration is the difference among problem's solution value and blank.