Analysing water for acids and bases

Question 1

What is the equivalence point of an acid-base reaction?

Answer 1

The point at which chemically equivalent amounts of acid and base, according to the equation, are present.

Question 2

What is the end point of an acid-base reaction?

Answer 2

The point at which the indicator changes colour. The indicator should be chosen so that the end point is close to the equivalence point.

Question 3

What is a standard solution?

Answer 3

A solution of accurately known concentration.

Question 4

What is alkalinity?

Answer 4

Measure of the ability of water to withstand sudden pH change caused by acid input.

Question 5

How is water made more acidic?

Answer 5

Water is made acidic when natural acids or acids that are generated by human activity dissolve in it.

Question 6

How is water made more basic?

Answer 6

Water is made basic when natural bases or bases that are generated by human activity dissolve in it.

Question 7

Why does water need to be analysed?

Answer 7

Water needs close to an optimum pH for many of its uses. Knowing how much acid or base there is, is important when its pH needs to be adjusted.

Question 8

How can water be analysed?

Answer 8

Using a volumetric analysis, which involves solutions of accurately known concentration and careful measurement of volumes.
eg. qualitative: which chemicals are present or quantitative: how much chemicals are present.

Question 9

What is a primary standard?

Answer 9

A sample that is so pure, that its concentration can be accurately calculated from its mass. Substance used to create a standard solution.

Question 10

What is a burette?

Answer 10

A calibrated glass tube that delivers variable volumes accurately. Volume dispensed is the titre. Must be rinsed with substance used.

Question 11

What is a pipette?

Answer 11

A calibrated glass tube that delivers a fixed volume accurately. Must be rinsed with substance used. Holds the alloquit.

Question 12

What is a titre?

Answer 12

The volume delivered by a burette.

Question 13

What is a aliquot?

Answer 13

Volume delivered by a pipette.

Question 14

What is an indicator?

Answer 14

A weak acid whose conjugate acid changes colour.

Question 15

How to calculate the concentration of a standard solution?

Answer 15

1. divide its mass by its given molar mass

2. use formula c= n/v by dividing its mass by amount of volume

Question 16

What are the steps for an acid-base titration?

Answer 16

1. write balanced equation between base and acid, taking not of mole ratio
2. determine the average volume of the titre
3. calculate concentration of standard solution if unknown and then calculate amount of mole
4. using mole ratio determine amount of mole of the unknown
5. using c= n/v, calculate concentration of unknown

Question 17

What would happen to results of a titration when the burette is rinsed with water?

Answer 17

The burette solution is diluted with water so more is used.

Question 18

What is a volumetric flask?

Answer 18

Used prepare standard solutions. Needs to be rinsed with distilled water.

Question 19

What is a conical flask?

Answer 19

Sits underneath burette where titration takes place. Must be rinsed with water. Is the container for the alloquit.

Question 20

Which is the correct way to prepare glassware for a titration?

1. pipette, burette and conical flask should only be rinsed with water
2. pipette should be rinsed with water, burette rinsed with water and solution being analysed
3. conical flask should be rinsed with water and then dried to remove all water
4. both pipette and burette should be rinsed with water then the solution being analysed

Answer 20

4. both pipette and burette should be rinsed with water then the solution being analysed.
   This means that they will both contain only the moles of the solution being analysed and there will be not over or underestimation.