Unit 3 - Researching Chemistry

Question 1

What is volumetric analysis?

Answer 1

Involves accurately measured volumes of solutions

Question 2

What is gravimetric analysis?

Answer 2

Involves accurate weighing of materials

Question 3

What is a quantitative reaction?

Answer 3

A reaction that has a measurable change (eg. change in mass/volume)

Question 4

What is a qualitative reaction?

Answer 4

A reaction in which there is a visible change that cannot be measured (eg. colour change)

Question 5

How can the concentration of a solution be obtained volumetrically?

Answer 5

Reacting the solution with a standard solution

Question 6

What 3 conditions must be met in order for the concentration of a solution to be determined volumetrically?

Answer 6

• Reaction goes to 100% completion
• The stoichiometric (balanced) equation for the reaction is known
• A suitable end-point, or a method to detect the end-point, of the reaction is known

Question 7

What is a standard solution?

Answer 7

A solution of accurately known concentration

Question 8

What kind of substance must be used to prepare a standard solution?

Answer 8

Primary standard

Question 9

What 4 conditions must be met by a primary standard?

Answer 9

• High degree of purity (>99.9%)
• Must be stable in air and in solution
• Must be readily soluble (usually in water)
• Must have a reasonably high formula mass

Question 10

What is a hygroscopic material?

Answer 10

A material that attracts moisture from the atmosphere

Question 11

What is a deliquescent material?

Answer 11

A material that attracts so much water that it forms a solution

Question 12

How is a standard solution prepared?

Answer 12

• Dissolve weighed substance in deionised water
• Pour into graduated flask using a filter funnel
• Rinse beaker, stirring rod, filter funnel etc with deionised water
• Fill flask to marked volume (bottom of meniscus)
• Stopper and invert 10 times to mix

Question 13

What are some common primary standards for acid/base reactions?

Answer 13

Oxalic acid and anhydrous sodium carbonate

Question 14

What is a common primary standard for complexometric titrations?

Answer 14

EDTA

Question 15

What are some primary standards for redox reactions?

Answer 15

Oxalic acid and potassium iodate

Question 16

What is the equivalence point of a reaction?

Answer 16

The point at which the reaction is just complete - stoichiometric amounts of titrand (solution in flask) and titrand (solution in burette) are the same

Question 17

What is the end-point of a reaction?

Answer 17

The point at which a change is detected

Question 18

What is an indicator?

Answer 18

A substance which changes colour at the end-point

Question 19

What are the three main types of titrations?

Answer 19

• Acid/base - based on neutralisation reactions
• Redox - based on redox reactions
• Complexometric - based on complex formation reactions

Question 20

What is the general experimental technique for titrations?

Answer 20

• Rinse a pipette with a solution of unknown concentration and pipette a known volume into a clean dry titration flask
• Add a few drops of a suitable indicator
• Rinse a burette with a solution of accurately known concentration (standard solution) and fill this with titrant. Record position of bottom of meniscus
• Carry out a rough titration by running in titrant from burette and continuously swirling until end-point is detected. Reading taken and titre volume calculated
• Repeat the procedure until two concordat results (+/- 0.2cm3) and calculate the average
• Calculate unknown concentration