Q Acid-Base Indicators: Spectrophotometric Methods Dr. Prem D. Sattsangi Copyright © 2009

1. Molar Absorptivity Define Molar Absorptivity A.Calculate the molar absorptivity with the following data 1.25 x M solution has 0.45 O.D. absorbance at the λ max (455 nm). B.If the molar absorptivity of a compound is 33,350, calculate the absorbance of a 6.5 x M solution.

2. Moles Calculate moles of NaOAc present in 5.00 mL of a M soln. n = M x V

3. Calculate the [H 3 O + ] for a buffer solution containing M AcO - (= NaOAc) and M AcOH. (Given K a for AcOH = 1.75 x )

4. Given the following data, calculate the Ka for a weak acid. K a = [H 3 O + ] [B - ] [HB] [H 3 O + ] = 3.45 x M, [B - ] = M,[HB] = 0.01 M

5. For a buffer, pH = pK a + log [X - ] [HX] At what concentration of [X - ] and [HX] would pH = pK a ?

6. During a titration experiment we take mL of AcOH and add 25 mL of water to make it 50 mL. If the first pH reading is 2.45, (Given: pH = -log [H 3 O + ]) a)What is the [H 3 O + ] of the diluted solution? b)What would be the [H 3 O + ] of the solution before dilution? Equation for dilution must be used V 1 x M 1 = V 2 x M 2 c)Calculate the K a of acetic acid using this data. AcOH + H 2 O ↔ H 3 O + + AcO - (Given: [AcOH] = M) K a = [H 3 O + ] [AcO - ] [AcOH]

7. If the molarity of NaOH is M, and it takes 7.5 mL of phosphoric acid, calculate the molarity of phosphoric acid using the following data on its titration. H 3 PO 4 + NaOH  NaH 2 PO 4 + H-OH …Eq. 6 NaOH(0.113 M), 7.5 mL H 3 PO 4 (? M), mL a)At what volume would you expect the 3 rd equivalence point? b)Molarity of H 3 PO 4 : [M = n/V*L]

8. H 3 PO 4 can ionize in 3 steps. Write chemical equations for ionization steps 1 and 2. Write expression for K a2 =

9. Write an expression for K sp of Ag 2 SO 4.

10. KHT(s) is saturated in distilled water. The saturated solution (25.00 mL) required 16.5 mL of M NaOH to reach the end point. a)Write an equation for this titration. b)Calculate the solubility of KHT in distilled water. _______M c)Calculate K sp for KHT [=________ (Unit _____)]

11. An U.K. solution was given in 100 mL volumetric. After making it up to the mark, it was saturated with KHT, filtered and titrated. If mL of the filtrate took 4.50 mL of M NaOH, calculate the molarity of the unknown. [K sp for KHT = 5.1 x M 2 ]

12. In a titration of solubility of KHT in M KNO 3, one used 4.53 mL of M NaOH solution for mL of the saturated filtrate. a)Calculate the solubility of KHT in M KNO 3. (=_____M) b)K sp for KHT in presence of M KNO 3.

Molar Absorbtivity ”ε” ε = Absorbance Concentration(M) Calculate the molar absorptivity “ε” for morphine, if a 3.68 x M solution has a 0.45 O.D. absorbance at the גּ max (328nm)

Calculating Moles of a Solution n = M x V n = number of moles of solution M = molarity of the solution V = volume of the solution in liters (L) Calculate moles of NaOAc (sodium acatate) present in 5.00mL of a 0.250M solution.

Calculation of Hydrogen Ion Concentration [H 3 O + ] = Ka x [AcOH] [AcO-] Calculate the [H 3 O + ] for a buffer solution containing 4.25 x M AcO - (acetate ion) and 2.25 x AcOH (acetic acid). [Ka for AcOH = 1.75 x ]

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