Planning

Question 1

Uncertainty ie. Error

Definition

= Absolute uncertainty

Answer 1

± 1/2 the smallest division of an instrument

Question 2

Percentage Uncertainty

Formula

Answer 2

Absolute uncertainty/ measured value x 100%

Question 3

Absolute uncertainty

Determining

Answer 3

Addition/ subtraction: ≥ 1 reading using the same apparatus

Multiplication/ division (eg. density from mass & volume)
- Calculate sum of percentage uncertainties of all readings
- Work backwards

Question 4

Volumetric Analysis

Types

Answer 4

• Acid-base
• Redox → Expt. 4-5
• Back → Expt. 3
• Double indicator
• Precipitaton

Question 5

Volumetric Analysis

Acid-base Indicators

Answer 5

• Methyl orange (SA-SB/WB)
  
  • Range: 3.2-4-4
  • Colour change: red → orange → yellow
• Screened methyl orange (SA-SB/WB)
  
  • Range: 3.2-4.4
  • Colour change: violet → grey → green
• Thymol blue (SB-SA/WA)
  
  • Range: 8.0-9.6
  • Colour change: yellow → green → blue
• Thymolphthalein (SB-SA/WA)
  
  • Range: 9.4-10.6
  • Colour change: colourless → colourless/ light blue → blue
• Bromothymol blue
  
  • Range: 6.0-7.6
  • Colour change: yellow → green → blue
• Phenolphthalein
  
  • Range: 8.3-10.0
  • Colour change: colourless → colourless/ light pink → pink

Colour change arranged from acidic to alkaline

Thymolphthalein & phenolphthalein end-point colour is arranged from acidic to alkaline titrant

Question 6

Volumetric Analysis

Redox Indicators

Answer 6

Usually OA colour change is sufficient with exception of iodometric ones → starch
- Colour change: Blue-black → colourless

Question 7

Volumetric Analysis

Procedure → Micro-dilution

Answer 7

1. Using a dropping pipette, add 10 drops of FA2 into a boiling tube
2. Add an indicator/ acid if necessary
3. Wash the dropping pipette with deionised water and FA1
4. Using the same dropping pipette, add FA1 drop by drop into the boiling tube and shake to ensure good mixing
5. Count the number of drops of FA1 needed for colour change to be observed
6. Record the number of drops of FA1 used

Question 8

Volumetric Analysis

Analysis → Micro-dilution

Answer 8

1. Let D_FA1 & D_FA2 be the number of drops of FA1 & FA2 respectively
2. Let V_FA1 & V_FA2 be the volume of FA1 & FA2 respectively
3. Dilution factor = D_FA1/ D_FA2
   4.