AP CHEM Unit 7 Day 6 REVIEW

A strong acid is added to a buffer with a pH of 4. Which component of the buffer will help minimize any pH change caused by the added acid?
NO Calculator!

• H₂O
• HA
• A^-
• H₃O⁺

Which pair is the most effective buffer?
NO Calculator!

• 0.5 M HIO and 0.5 M NaIO
• 0.1 M HF and 0.9 M NaF
• 0.9 M HIO and 0.1 M NaIO
• 0.1 M HF and 0.7 M NaF

Which of the following will NOT make a buffer?
CH₃NH₂ is a weak base.
NO Calculator!

• 105.0 mL of 0.15 M CH₃NH₂;
  95.0 mL of 0.10 M HCl
• 125.0 mL of 0.15 M CH₃NH₂;
  120.0 mL of 0.25 M CH₃NH₃Cl
• 165.0 mL of 0.10 M HF;
  135.0 mL of 0.050 M KOH
• 150.0 mL of 0.10 M HClO;
  135.0 mL of 0.075 M HCl

In which solution is the pKa most similar to the pH?
HA is a weak acid in all answer choices.
NO Calculator!

• 0.10 mol of HA and 0.11 mol of A- in 1 L of solution
• 0.33 mol of HA and 0.67 mol of A- in 1 L of solution
• 0.10 mol of HA and 0.025 mol of Ba(OH)₂ in 1 L of solution
• 0.10 mol of HA and 0.033 mol of NaOH in 1 L of solution

Which combination is the best choice to prepare a buffer with a pH of 5?
NO Calculator!

• CH₃NH₂ (pK_b=3.36);
  CH₃NH₃Cl
• HCHO₂ (pK_a=3.74);
  NaCHO₂
• C₅N₅N (pK_b=8.76);
  C₅H₅NHCl
• HClO (pK_a=7.53);
  NaClO

A buffer has a pH of 4.85 and contains formic acid and potassium formate.  What can you conclude about the concentrations of the components of the buffer?  
The K_a of formic acid is 1.8 x 10^-4.
NO Calculator!

• Formic acid > Potassium formate
• Formic acid < Potassium formate
• Formic acid = Potassium formate
•  ¯\_(ツ)_/¯

What is the pH of a buffer that is 0.08 M NaA and 0.1 HA.
The K_a of HA = 1.0 x 10^-4.
NO Calculator!

• 2.00
• 3.90
• 4.00
• 4.10

Determine the pH of a solution that results upon mixing 100.0 mL of 0.20 M of a weak acid and 100.0 mL of 0.10 M sodium hydroxide.  
This weak acid is monoprotic and has a K_a=1.0x10^-4.
NO Calculator!

• 3.83
• 4.00
• 4.18
• 5.51

Blood is a buffer system between carbonic acid and hydrogen carbonate ions. While the pH of blood is 7.4, the pKa of carbonic acid is 6.1. Why is this beneficial to our survival?
NO Calculator!

• [H₂CO₃] < [HCO₃^-] which makes the buffering capacity greater for an acid, enabling our blood to buffer the lactic acid produced while exercising
• [H₂CO₃] < [HCO₃^-] which makes the buffering capacity greater for a base, enabling our blood to buffer the basic effects of low carbon dioxide levels produced from hyperventilation
• [H₂CO₃] > [HCO₃^-] which makes the buffering capacity greater for an acid, enabling our blood to buffer the uric acid produced when cells break down
• [H₂CO₃] > [HCO₃^-] which makes the buffering capacity greater for a base, preventing calcium from binding to blood transport proteins like albumin

Which of the following combinations of equimolar substances could make a buffer?
NO Calculator!

• HNO₂ and NaNO₃
• HCl and NaCl
• NH₄Cl and NH₃
• NaOH and HCl