Document4 ces Mailings Review View Table Design Layout AaBbCcDdEe AaBbCcDdEeAaBb

Question

Document4 ces Mailings Review View Table Design Layout AaBbCcDdEe AaBbCcDdEeAaBbCcD Normal No SpacingHeading 1 1. A beaker with 125 mL of an acetic acid buffer with a pH of 5.000 is sitting on a benchtop. The total molarity of acid and conjugate base in this buffer is 0.100 M. A student adds 7.30 mL of a 0470 Micl solution to the beaker. How much will the pH change? The pka of acetic acid is 4.740 2. A sample of 7.70 L of NHs (ammonia) gas at 22 -C and 735 torr is bubbled into a 0.350 L solution of 0.400 M Hal (hydrochloric acid). The Kb value for NHs is 1.8*10-5 3. What volume of 10.0 M NaOH is needed to prepare a buffer with a pH of 7.79 using 31.52 g of TrisHC? The buffe A?S c uted to 1,00 L To half of it (500. mL), you add 0.0200 molof hydrogen ions without charging the voume. w H of the final solution? IF

Explanation / Answer

pH of acidic buffer = pka + log(ch3coo^-/CH3COOH)

pka of CH3COOH = 4.74

Total no of mol of buffer = V*M

                        = 125*0.1 = 12.5 mmol

total buffer = ch3coo- + ch3cooh

5 = 4.74 + log(x/(12.5-x))

x = 8.07

no of mol of CH3COO- = x = 8.07 mmol

no of mol of CH3COOH = 12.5 - 8.07 = 4.43 mmol

after addition of HCl,

No of mol of HCl added = 7.30*0.47 = 3.43 mmol

pH = 4.74+log((8.07-3.43)/(4.43+3.43))

     = 4.5

change in pH = 5-4.5 = 0.5

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