Chapter 9 Acid-Base Volumetric Analysis

Question 1

What is an acid-base titration?

Answer 1

• It involves a reaction between an acid solution and a base solution.
• The purpose of the titration is to find the concentration of the acid or base in the solution of unknown concentration.

Question 2

What is a standard solution ?

Answer 2

It is the solution in an acid-base titration with a known concentration.

-The other solution’s concentration isn’t known.

Question 3

What is the Equivalence Point ?

Answer 3

• It is the theoretical point in the titration.
• In practice the equivalence point of an acid-base titration is not visibly obvious and so requires the use of an acid-base indicator to show that equivalence has occured.

Question 4

What is the End Point of a titration?

Answer 4

It is the point where the indicator changes colour signalling that equivalence has occurred.

-In practice, the end point is typically a close approximation of the equivalence point.

Question 5

What is a primary standard solution?

Answer 5

• It is one of accurately known concentration that can be used in a titration to find the concentration of other reagents.
• It is made by carefully weighing a sample of primary standard, dissolving this in distilled water and then making the solution up to a precise volume in a volumetric flask.

Question 6

Why are common acids like Hydrochloric acid or sulfuric acid and bases like sodium hydroxide or potassium hydroxide not suitable as primary standards?

Answer 6

• This is because these cannot be obtained in a suitable pure form.
• Sodium hydroxide and potassium hydroxide for example are affected by exposure to air as they absorb variable amounts of water vapour while also reacting with atmospheric CO2(g) forming Na2CO3 and K2CO3.

Question 7

Typically a primary standard must:

Answer 7

• be able to be obtained in a very pure form consistent with its chemical formula.
• be sufficiently stable so that on exposure to air it does not readily change its water content or react with other gases (like CO2) in the air
• have a relatively high molar mass

Question 8

What is a Secondary Standard solution?

Answer 8

It is when common acids/bases that cant be prepared as primary standard solutions but still have their concentration found by titration.

Question 9

What is a Secondary Standard solution used for?

Answer 9

A secondary standard solution can then be used as the solution of known concentration in other titrations.

Question 10

Why is the Secondary Standard Solution not preferred to be used?

Answer 10

The technique for finding the concentration of a secondary standard involves extra measurements and procedures, its concentration will be subject to greater uncertainty (error) than the concentration of a primary standard solution.

Question 11

How can the titre be found?

Answer 11

It is found by subtracting the initial burette reading from the final burette reading.