Appendix_I_Practice+Problems_LZM__v+F10

Appendix_I_Practice+Problems_LZM__v+F10 - MCB120L AI-1...

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MCB120L AI- 1 Practice Problems: Experiment 1 Consult as needed: Table 1.1 pK a values for buffers in dilute solution 1.1. What volume of glacial acetic acid (17.6 N) and weight of sodium acetate·3 H 2 O (F.W. = 136) is required to make 100 ml of 0.20 M buffer, pH 4.06? (Note: F.W. stands for formula weight in g/mol). 1.2. a) What volume of glacial acetic acid (17.6 N) and weight of sodium acetate·3 H 2 O (F.W.= 136) is required to make 100 ml of 0.20 M buffer, pH 5.06? b) How is 100 ml of 0.050 M buffer, pH 5.06, prepared from a stock of 0.20 M buffer, pH 5.06? 1.3 What quantities of reagents are needed to make 250 ml of a 0.050 M acetate buffer at pH 5.5? Available reagents: 1.0 N HCl, 1.0 N KOH, CH 3 COOK (FW 98.15, pKa 4.76) 1.4. a) What weights of sodium carbonate (FW = 106) and sodium bicarbonate (FW = 84) are required to make 100 ml of 0.20 M buffer, pH. 10.38? b) How is 100 ml of a 0.080 M buffer, pH 10.38, prepared from a stock of 0.20 M buffer, pH 10.38? 1.5. What volume of hydrochloric acid (11.7 N) and weight of Tris (MW = 121) are required to make 100 ml of 0.20 M buffer, pH 8.71? 1.6. What volume of concentrated HCl (11.7 N) and weight of Tris base (MW = 121 g/mole) is needed to make 100 ml of 0.20 M buffer, pH 8.45? 1.7. a) Glycine has both weak acid (the carboxyl group) and weak base (the primary amino group) properties, making it a useful as a buffer. What are the pKa’s of glycine’s carboxyl and amino groups? What is the structure of pure glycine in H 2 O? b) What is the pH of 0.2M glycine in H 2 O? c) If 50 mls of 0.20 M glycine is mixed with 50 mls of 0.1 M KOH, what is the resulting pH? d) How will the pH change if the temperature is increased above 20 ° C? 1.8. a) If 50 mls of 0.20 M glycine is mixed with 50 mls of 0.1M HCl, what is the resulting pH? b) How will the pH change if the temperature is increased above 20 0 C? 1.9. a) Phenol Red is a weakly acidic dye which is yellow in the HA form and red in the A form. What concentration of Phenol Red is required to obtain an absorbance of 0.50 at 550 nm at pH 7.8? Note: ε 550 of A = 2.5 x 10 4 M -1 cm -1 ; ε 550 of HA = 0; pKa = 7.8. . b) What would the absorbance of the solution in part (a) be if the pH was 8.8? 1
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MCB120L AI- 2 1.10. Determine the pKa of a dye. The dye was diluted into several different buffers and the A 450 was measured (Table I). Using the data in Table I along with the ε 450 (anionic form) = 50,000 M -1 cm -1 , find the pKa of the dye. Table I 1.11. Calculate the pKa of m-ultra red when equimolar amounts of the pH indicator m-ultra red are mixed in separate test tubes with large molar excesses of buffers at seven different pH values. All buffer plus dye solutions were diluted to the same final volume and the absorbances at 550 nm were read. equimolar concentrations of m-ultra red at various pH values 1.12. Challenge Problem #1: When an enzyme catalyzes the hydrolysis of X to Y , one mole of protons is released per mole of substrate utilized. When this reaction was carried out at 24°C in a 3 ml reaction mixture buffered only by Tris buffer at an initial pH of 8.5, 20 μmoles of X were converted to Y. What is the minimum concentration of Tris buffer required to prevent the pH from decreasing below 8.3?
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This note was uploaded on 11/21/2010 for the course MCB 120L 69059 taught by Professor Fairclough during the Fall '10 term at UC Davis.

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Appendix_I_Practice+Problems_LZM__v+F10 - MCB120L AI-1...

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