please help with #7 and #8. 7. A buffer is prepared by adding 20.0 g of acetic a

Question

please help with #7 and #8.

7. A buffer is prepared by adding 20.0 g of acetic acid (HC2Hs02) and 20.0 g of sodium acetate (NaC2Ha02) to enough water to form 2.00 L of solution. (K, 1.8 x 10) a. Determine the pH of the buffer. Write the complete ionic equation for the reaction that occurs when a few drops of hydrochloric acid are added to the buffer. b. Write the complete ionic equation for the reaction that occurs when a few drops of sodium hydroxide solution are added to the buffer. c. How many moles of sodium hypobromite (NaBrO) should be added to 1.00 L of 0.050 M hypobromous acid (HBrO) to form a buffer solution of pH 9.15? Assume no volume change occurs when the NaBrO is added. (K- 2.5 x 109) 8.

Explanation / Answer

Buffer

m = 20 g of Acetic Acid

MW of Acetic Acid = 60 g/mol

mol = mass/MW = 20/60 = 0.33 mol

m = 20 g NaAc

MW of NaAc = 82.03 g/mol

mol = mass/MW = 20/82.03 = 0.2438 mol

V = 2L

a)

buffer pH

apply henderson hasselpbach equation

pH = pKa + log(NaAc/HAc)

pH = -log(Ka) + log(NaAc/HAc)

pH = -log(1.8*10^-5) + log(0.2438 /0.33) = 4.613

b)

Write complete ionic equation for the reaction that occurs when a few drops of HCl are added

HCl --> H+ and Cl-

HAc <<--->> H+(aq) + Ac-(aq)

there is no reaction, only displacement/shift of equilibrium

c)

Net ionic equation when OH- is added

NaOH ---> Na+ and OH-

HAc <--> H+ and A-

H+(aq) + OH-(aq) ----> H2O(l)

NOTE: Consider posting question 8 in another set of Q&A, we are not allowed to answer to multiple questions in a single set of Q&A

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