Question

1. Please calculate the pH of a solution containing 2.0M citric acid and 1.0M sodium citrate. 2. Please calculate the pH of a solution containing 1.0M tartaric acid and 1.OM potassium tartarate. 3. Please calculate the pH of a solution containing 0.25M CH NH, and 0.37M C.HNH,CI. 4. Please design a buffer system to maintain a pH of 7.20. 5. Please design a buffer system to maintain a pH of 3.70. 6. For each of the following solutions please calculate the initial pH and then the pH after adding 0.01M HCI. a. 500 mL H2O b. 500 ml of 0.125 M HC H2O, and 0.115 M NaC,H,02 C. 500 mL of 0.155M CH3NH, and 0.145M CHENH,CI 7. For each of the following solutions please calculate the initial pH and then the pH after adding 0.01M NaOH. a. 250 ml. H20 b. 250 mL of 0.125 M HC.H2O, and 0.115 M NaC,H,02 c. 250 mL of 0.155M C2H5NH2 and 0.145M CHENH,CI 8. For the pain reliever aspirin given on the previous homework. Please calculate the amount of each component needed to create a "buffered" aspirin. Would these amounts make a reasonable pill?

Answer 1

1. The solution is buffer

Using Hendersson- Hasselbalch equation

pH = pKa + log [sodium citrate/citric acid]

Or, pH = 3.1 + log (1.0/2.0)

Or, pH = 3.1 - 0.30

Or, pH = 2.80.

2.

The solution is buffer

pKa of tartaric acid = 2.98

pH = pKa + log [Potassium tartarate]/[Tartaric acid]

pH = 2.98 + log (1.0/1.0)

Or, pH = 2.98

3.

The solution is buffer.

Pka of C₂H₅NH₃⁺ = 10.87

Hence,

pH = pKa + log [C₂H₅NH₂]/[C₂H₅NH₃⁺]

Or, pH = 10.87 + log (0.25/0.37)

Or, pH = 10.87 - 0.17 = 10.70.

4.

To prepare a buffer system pKa value of the acid should be close to the pH.

Given, pH = 7.20

pH = pKa + log [Na₂HPO₄]/[NaH₂PO₄]

Therefore, equimolar concentration of Na₂HPO₄/NaH₂PO₄ buffer will be used.

pKa of NaHPO₄ = 7.20

So, pH = 7.20

5.

pKa of formic acid = 3.75.

Hence,

3.70 = 3.75 + log [HCOONa/HCOOH]

Or, log [HCOONa/HCCOH] = - 0.05

Or, [HCOONa/HCOOH] = 0.89.

Hence, take 0.89 mole of HCOONa and 1 mole HCOOH and dissolved in 500 mL water to get the desired buffer.