BCH210H1 Lecture Notes - Lecture 2: Dipeptide, Fluid Compartments, Heterocyclic Compound

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22 May 2012

School

UTSG

Department

Biochemistry

Course

BCH210H1

Professor

Stavroula Andreopoulos

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BCH210H1 Full Course Notes

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Document Summary

Titration curves titration analytical method to determine the amount of acid in solution. Measured volume of acid is titrated by adding solution of a base of known concentration. Ph of the solution is determined plot of ph versus amount of oh- added created a titration curve. Polyprotic acid substance has more than one dissociable proton and equal equivalents of. Oh- to the number of dissociable protons are needed to neutralize it. Buffers solutions that resist changes in ph as acid or base is added. Buffer molarity the sum of the concentrations of the acid and conjugate base forms. Phosphate system buffers intracellular fluid of cells at physiological ph (range between two buffer systems maintain intracellular ph phosphate system and histidine system.

Related Questions

An inflection point in the titration curve:

		occurs during a titration when one equivalent of base is added to a weak acid solution.
		is a point near which more base can be added without changing the pH significantly.
		is reached when the pH equals the pK_a of the acid.
		occurs when the mixture contains an equal concentration of the weak acid and its conjugate base.
		can tell you the pK_a of the weak acid used to make the buffer.

QUESTION 1

Which pair of compounds will form a buffer in aqueous solution?

	a.	HCN and NaCN
	b.	NaCN and NaOH
	c.	HCl and NaOH
	d.	HCl and NaCl
	e.	HCN and HCl
	f.	NaCN and KCN

10 points

QUESTION 2

A buffer solution is titrated with 0.032 M HCl solution. The initial volume of the buffer is 25.00 mL. The equivalence point of the titration is determined to be 4.88 mL. What is the concentration of conjugate base (in M) in the buffer solution? Assume the stoichiometry of acid to base is 1:1.

10 points

QUESTION 3

A buffer solution is titrated with 0.046 M NaOH solution. The initial volume of the buffer is 25.00 mL. The equivalence point of the titration is determined to be 8.77 mL. What is the concentration of acid (in M) in the buffer solution? Assume the stoichiometry of acid to base is 1:1.

10 points

QUESTION 4

The concentrations of acid and conjugate base in a buffer are determined experimentally to be 0.044 M and 0.059 M, respectively. If the total buffer concentration given on the bottle (the true value) is 0.102 M, then what is the percent error of the experimental value?

10 points

QUESTION 5

There are several calculations that need to be done in order to prepare a specific volume of buffer solution at a particular concentration and pH. There is a worked example in your lab manual on p. 119.

First, determine the correct A^-/HA ratio: The pK_a of acetic acid is 4.76, and the buffer solution needs to maintain a pH of 4.25. The concentration of acetate (CH₃CO₂^-) should be X times that of the concentration of acetic acid (CH₃CO₂H). What is X?

10 points

QUESTION 6

Once the correct ratio of A^- to HA is known, determine the actual concentration of A- needed to make a buffer at a particular concentration.

The ratio of acetate to acetic acid in a buffer is 0.176. That is, the concentration of acetate should be 0.176 times that of the concentration of acetic acid. What is the concentration of acetate (in M) needed to prepare a 0.416 M buffer using acetic acid and acetate?

10 points

QUESTION 7

What volume of acetate solution (in mL) is needed to make 250.0 mL of a buffer solution? The concentration of acetate in the buffer must be 0.0594 M, and the concentration of the acetate stock solution is 0.500 M.

BCH210H1 Lecture Notes - Lecture 2: Dipeptide, Fluid Compartments, Heterocyclic Compound

BCH210H1 Full Course Notes

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