Molar Mass and Buffer Solutions

The video tutorial covers lesson 5 of unit 11 on buffers, focusing on preparing buffer solutions. It explains the use of the PKA equation and how to calculate the mass of sodium formate needed for a buffer solution with a specific pH. The tutorial also highlights common errors students make, such as incorrect molar mass calculations. A parallel problem is presented for practice, emphasizing the conversion of PKB to PKA and the importance of significant figures.

What is the primary purpose of a buffer solution?

• To neutralize a solution

• To decrease the pH of a solution

• To maintain a stable pH in a solution

• To increase the pH of a solution

In the given problem, what is the target pH for the buffer solution?

• 4.50

• 3.95

• 4.00

• 3.50

How many moles of H2CO2 are present in 1.25 liters of 0.50 M solution?

• 0.750 moles

• 0.250 moles

• 0.500 moles

• 0.625 moles

What is the molar mass of sodium formate used in the calculations?

• 68.008 g/mol

• 88.008 g/mol

• 58.008 g/mol

• 78.008 g/mol

What common error do students make when calculating the molar mass of sodium formate?

• Forgetting to include the mass of sodium

• Forgetting to include the mass of hydrogen

• Forgetting to include the mass of oxygen

• Forgetting to include the mass of carbon

What should you do if you forget to convert Kb to Ka in a problem?

• Use an estimated value for Ka

• Use the Kb value directly

• Rework the problem with the correct conversion

• Ignore the conversion

What is the sum of pKa and pKb at 25°C?

• 14

• 16

• 12

• 10

How many moles of A- are present in 2 liters of 0.3 M solution?

• 1.2 moles

• 0.3 moles

• 0.6 moles

• 0.9 moles

What is the final calculated mass of the ammonium salt in the parallel problem?

• 130 grams

• 120 grams

• 100 grams

• 110 grams

What was the error identified in the chemical formula during the solution of the parallel problem?

• Incorrect number of nitrogen atoms

• Incorrect number of hydrogen atoms

• Incorrect number of chlorine atoms

• Incorrect number of carbon atoms