Chemguide: Support for CIE A level Chemistry

Learning outcome 7.2(g)

This statement is about how buffer solutions work.

Before you go on, you should find and read the statement in your copy of the syllabus.

Statement 7.2(g)(i)

Read the first half of the Chemguide page about buffer solutions. You can ignore the second half about calculations for the moment. That will be needed for statement 7.2(h).

Statement 7.2(g)(ii)

This is about the uses and importance of buffer solutions, including keeping the blood at a constant pH between 7.35 and 7.45.

There are several things which buffer the pH of the blood, one of which is the following equilibrium involving hydrogencarbonate ions.

The carbon dioxide in the blood comes from, for example, the break-down of carbohydrates in the body.

If the hydrogen ion concentration in the blood increases (if the pH falls), then this equilibrium will move to the left to remove the extra hydrogen ions.

If the hydrogen ion concentration in the blood decreases (if the pH rises), then this equilibrium will move to the right to replace the missing hydrogen ions.

This is just a simple application of Le Chatelier's Principle.

The syllabus talks about "uses" of buffers - which implies more than one use. You need to be able to quote another use just in case you are asked.

The simplest to understand is their use in the lab to check the readings on a pH meter. For accurate work, you would make up a buffer solution with a pH of, say, 4.0, and then adjust your pH meter so that it was reading exactly that value.

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© Jim Clark 2011 (last modified April 2014)