I need some help with this homework. ( Can you please show the work for them.) T

Question

I need some help with this homework. ( Can you please show the work for them.) Thanks

1) Find the pH and concentrations of CH3CH2CH2CO2H and CH3CH2CH2CO2­ in a 0.0250 M solution of butanoic acid.

2) What is the pH of a buffer prepared by mixing 20.00 mL of 0.0300 M ammonium chloride with 40.00 mL of 0.0450 M ammonia? What is the resulting pH if 1.00 mL of 0.10 M HCl is added to this solution?

3) Consider a titration of 20.00 mL 0.02500 M acetic acid with 0.0500 M NaOH. What is the pH of the solution when the following volumes of base are added? Vb = 0, 2.5, 5, 9.5, 10, 10.5, and 15 mL.

4) Starting with the fully deprotonated (basic) species of cysteine write the stepwise base hydrolysis reactions. Be sure to add the protons in the correct order. Calculate the values of Kb,1, Kb,2 and Kb,3. What is the pH and concentration of all species in a 0.0250 M solution of cysteine (the neutral form)?

Explanation / Answer

1)

Find the pH and concentrations of CH3CH2CH2CO2H and CH3CH2CH2CO2­ in a 0.0250 M solution of butanoic acid.

concentration of butanoic acid = 0.0250 M

Ka = 1.5×10–5

CH3CH2CH2CO2H   ----------------------> CH3CH2CH2CO2-   +   H+

0.0250                                                            0                       0

0.0250 - x                                                       x                        x

Ka = x^2 / 0.0250 - x

1.5×10–5 = x^2 / 0.0250 - x

x = 6.05 x 10^-4

[H+] = 6.05 x 10^-4

pH = -log (H+) = -log (6.05 x 10^-4)

pH = 3.22

[CH3CH2CH2CO2-] = 6.05 x 10^-4 M

[CH3CH2CH2CO2H] = 0.0244 M

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