Lab Exam 1

What is the predominant form of glycine at a very low pH?

•  

  +NH3-CH2-COO-

•  

  NH2-CH2-COO-

•  

  NH3-CH2-COOH

•  

  +NH3-CH2-COOH

Which groups of free amino acids are weak acid groups that ionize in aqueous solutions?

•  

  COO- and NH3

•  

  COOH- and NH3+

•  

  COO- and NH3+

•  

  COOH and NH3

Tags

NGSS.HS-PS1-2

Looking at the following glycine titration curve: At which point is glycine in its predominately negative form?

•  

  pK1

• PI

• pK2

Tags

NGSS.HS-PS1-2

Looking at the following glycine titration curve: What is the pH at the second dissociation?

• 9.60

• 2.34

• 5.97

Looking at the following glycine titration curve: What point is glycine predominately in its zwitterion ion form?

•  

  pH 9.60

•  

  pH 2.34

•  

  pH 5.97

Your lab requires you to prepare a 100 mL of 0.3M phosphate buffer, with a pH of 7.8.

Below are the different proton dissociation equations for phosphoric acid. Which one would you choose, given the pKa value, to make this buffer solution?

• pKa = 7.21

• pkA = 12.32

• pKa = 2.12

To make this buffer solution, we use certain salts to avoid the common ion effect. Knowing the equation of this reaction, which of the following would represent our weak acid?

•  

  HPO₄

•  

  H₂PO₄

•  

  KH₂PO₄

• Na₂HPO₄

Using the Henderson-Hasselbalch equation, what is the value of [A^-]/[HA]?

• 6

• 4

• 3.21

• 2.06

After substituting the value of [A-] into the original equations of Na₂HPO₄ + KH₂PO₄ = 0.3 M, what is the value of [A-]?

•  

  0.12

• 0.24

• 0.15

• 0.06

How many grams of [HA] would you need to make your buffer solution? Hint: Use M = Moles/Liter to solve for the number of moles. Remember you are making a 100 mL buffer solution. Use the molar mass of [HA] to go from moles to grams.

• 0.98

• 0.82

• 1.63

• 1.70