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K, of an Indicator Sol B 2mL 3X10M Green 2mL 0.160M Na 2. Determine how many mL of solution A (acetic acid-indicator solution) must be added to solution B (sodium acetate-indicator solution) to obtain a buffer solution that is equimolar (equal molar concentration) in acetate and acetic acid. You will need to refer to the Experi- mental Procedure, particularly the section on calculations, to answer this question. Show all calculations. Mol = MXL = 0.002L X0.160 M = 0.00032 Sol A 2ml 3x10-4M Five en 0.00032 0.0.60 42 a. Calculate moles Ac in solution B. 5ml 1.6M HA 20mL 0 200M KC| 0.00032 b. Calculate the molarity of HAc in solution A. 1-X 2x10-5,0.0064x2 2x10-52x10 {=00062 = 0.0064M mol Ac c. Calculate volume of solution A needed when the moles of Ac equals moles of HAC. 1.6 mol XV = 0.00032 L 0.2 M HAC ml. soln A V = 0.0002L 3. K is approximately 2 x 10 under your experimental conditions. Use Equation (5) to estimate the pH after the first addition of 1 mL of solution A. Show all calculations. a. Calculate pK, pka=-10g 2x10-5 5 -pk b. Calculate moles HAc in the 1 mL of solution A added to solution B. 1.6×10 c. Calculate moles Ac in solution B. 1.74x10-5 mol Ac d. Rearrange Equation (5) to solve for pH. M = 16M mol HAC x = 0.054 Mol Ac = 0.006348×005 = 174 x 10-5 16x0.0005 = 0.008 M mol HAc in ImL 0,008 M/50 = 1.6*10-4 pH X=-2 × 10 + √²4x10² 10 ++ (2x10-3) (0.0064) 2(0.0064) Me mul PH= 5-log [A] = 0.0064 x 0-054 = 0.006348M
Note: Always measure the pH to ±0.01. Preparation of Solutions Obtain about 15 mL of the following solutions in clean, dry, and labeled 30-, 50-, or 100-mL beakers: bromocresol green, acetic acid, sodium acetate, and potassium chloride. Solution A (bromocresol green indicator in acetic acid): Pipet into a 50-mL volumetric flask the following: 2.0 mL of 3.0 x 10-4 M bromocresol green solution 5.0 mL of 1.60 M acetic acid (HAC) 2.0 mL of 0.200 M KCl solution
Solution B (bromocresol green indicator in sodium acetate solution): Rinse the 50-mL wolumetric flask with distilled water, then pipet into it the following: 2.0 mL of 3.0 x 10-4 M bromocresol green solution 2.0 mL of 0.160 M sodium acetate solution Dilute the solution to the mark, mix the solu- tion, and pour it into a 250-mL beaker.
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