STK1213 ANALYTICAL CHEMISTRY 1. Which of the following are buffer systems? [3 marks] a. KF/HF - HF is a weak acid and KF is its salt. Hence, this is a buffer system. b. KCl/HCl - HCl is a strong acid. But a buffer consists of a mixture of a weak acid and its conjugate base. Hence, this is not a buffer system. c. Na 2 CO 3 /NaHCO 3 - NaHCO 3 contains a weak acid (HCO 3 - ) and Na 2 CO 3 is its salt. Hence, this is a buffer system. 2. Calculate the concentrations of hydrogen ion and hydroxide ion at 25 o C in 0.010M Ba(OH) 2 . [2 marks] Ba ( OH ) 2 ↔ Ba 2+¿ +2 OH −¿¿ ¿ One mole of Ba ( OH ) 2 produce onemole of Ba 2+¿ ∧2moles of OH −¿¿ ¿ 0.010 mole of Ba ( OH ) 2 produce 0.010 mole of Ba 2 +¿∧0.020 molesof OH −¿per litre ¿ ¿ ¿ K w =¿ 1.0 × 10 −14 =¿ ¿ ¿ 3. A CH 3 COOH/CH 3 COO - buffer is prepared by combining 100mL of 0.02M CH 3 COOH with 100 mL of 0.03M CH 3 COO - . [Ka = 1.76 × 10 -5 ] [5 marks] a. What is the pH of the resultant solution? No.ofmolesof 100 mLof CH 3 COOH=molarity×volume No.ofmolesof 100 mLof CH 3 COOH=0.02 × ( 100 1000 ) No.ofmolesof 100 mLof CH 3 COOH =2.00 × 10 −3 mol No.ofmolesof 100 mLof CH 3 COO −¿ =molarity× volume ¿ No.ofmolesof 100 mLof CH 3 COO −¿ =0.03× ( 100 1000 ) ¿ No.ofmolesof 100 mLof CH 3 COO −¿ =3.00× 10 −3 mol ¿ 1
STK1213 ANALYTICAL CHEMISTRY1. Which of the following are buffer
systems? [3 marks]a. KF/HF HF is a weak acid and KF is its salt.
Hence, this is a buffer system. b. KCl/HCl HCl is a strong acid.
But a buffer consists of a mixture of a weak acid and its conjugate
base. Hence, this is not a buffer system. c. Na2CO3/NaHCO3 NaHCO3
contains a weak acid (HCO3-) and Na2CO3 is its salt. Hence, this is
a buffer system.
2. Calculate the concentrations of hydrogen ion and hydroxide
ion at 25oC in 0.010M Ba(OH)2. [2 marks]
3. A CH3COOH/CH3COO- buffer is prepared by combining 100mL of
0.02M CH3COOH with 100 mL of 0.03M CH3COO-. [Ka = 1.76 10-5] [5
marks]a. What is the pH of the resultant solution?
b. What is the resulting pH of this buffer solution when 10mL of
0.01M HCl is added?
4. A buffer solution was prepared by dissolving 10.0 grams of
sodium acetate in 200.0 mL of 1.00 M acetic acid. Assuming the
change in volume is not significant, estimate the pH of the acetic
acid/sodium acetate buffer solution. The Ka for acetic acid is 1.7
x 10-5. [3 marks]
