U2 S3 L5
Polyprotic and Polybasic Species
Textbook Readings
MHR
•pages 609-611: Neutralization Reactions for Polyprotic and Polybasic Species
•page 612: Titration Curves for Polyprotic and Polybasic Species
Textbook Items
MHR
•page 611: items 21, 22, and 23
•page 616: items 9 and 10
•page 618: item 21
Upon completion of this lesson, you should be able to:
• define polyprotic species and polybasic species
• write single step and overall equations for an acid-base reaction
involving a species that can accept or donate more than one proton
• draw and interpret titration curves for acid-base reactions involving
polyprotic or polybasic species
Monoprotic Acids
• A mono-protic acid is a acid that can donate only one hydrogen.
– Ie: hydrochloric acid, nitric acid.
Polyprotic acids – (diprotic / triprotic)
• Polyprotic Acids - acids that have the ability to donate more than one
proton per molecule are classified as polyprotic species.
– Sulfuric acid is a good example:
Diprotic titration Curve:
Titration of Sulfuric acid with standard NaOH
Poly basic
• Polybasic – the ability to attracted more than one proton.
– Ie: carbonate ion.
Diprotic titration Curve:
Titration of sodium carbonate with standard HCl
1. Write the reaction steps and the net ionic equation for the quantitative reaction
between each pair of substances.
a. phosphoric acid and sodium hydroxide (two quantitative steps)
b. sodium sulfide and hydrochloric acid
c. selenic acid (H2SeO4) and sodium hydroxide
d. citric acid, H3C6H5O7, and sodium hydroxide (two steps)
2. Sketch a titration curve for the titration of a 0.100 M
phthalic acid, H2C8H4O4, with sodium hydroxide
solution. Assume two quantitative steps.
3.
A sodium hydrogen phosphate solution is titrated with
hydrochloric acid. Only one quantitative reaction is observed.
Write the Brønsted-Lowry equation for the reaction and
sketch the pH curve.