experimental techniques ii

Question 1

Measurements - time

Answer 1

Apparatus: digital stopwatch
Accuracy: 士0.01s

Question 2

Measurements - temperature

Answer 2

Apparatus: laboratory thermometer
Smallest division: 1°C
Accuracy: 士 0.5°C

Question 3

Measurements - mass

Answer 3

Apparatus: electronic balance
Accuracy: 士 0.01g

Question 4

Measurements- approximate value of liquid or solution

Answer 4

Apparatus: marked / graduated beaker

Question 5

Measurements - Accurate volume of liquid or solution

Answer 5

Apparatus: measuring cylinder
Smallest division: 1cm3
Accuracy: 士 0.5cm3

Question 6

Measurements - very accurate volume of liquid or solution

Answer 6

Apparatus 1: pipette
Apparatus 2: burette
Smallest division: 0.1cm3
Accuracy: 士0.05cm3
Apparatus 3: volumetric flask

Question 7

Measurements - volume of gas

Answer 7

Apparatus: marked / graduated gas syringe

Question 8

Collection of gases - solubility and relative density of common gases

Answer 8

Gas: solubility in water- relative molecular mass of gas - density compared to air
1. Ammonia: extremely soluble - 17.0 - less dense
2. Carbon dioxide: slightly soluble - 44.0 - denser
3. Chlorine: soluble - 71.0- denser
4. Hydrogen: not soluble - 2.0- less dense
5. Hydrogen chloride: very soluble - 36.5 - denser
6. Oxygen: very slightly soluble - 32.0 - slightly denser
7. Sulfur dioxide: very soluble - 64.0 -denser

Question 9

Relative molecular Mass

Answer 9

• The relative molecular mass (Mr) is the sum of all the relative atomic mass for all the atoms in a given formula

Question 10

Methods to collect gas - displacement of water

Answer 10

• This method is suitable for collecting gases which are insoluble or slightly soluble in water.
• eg. Oxygen, nitrogen, carbon dioxide, hydrogen

Question 11

Methods to collect gas - downward displacement of air

Answer 11

• Suitable for any gas, especially those soluble in water
• aka upward delivery of gas
• connect the delivery tube to an inverted test-tube for the gas to be collected
• this method is used to collect gases that are les dense than air
• eg. Hydrogen, ammonia

Question 12

Methods to collect gas - upward displacement of air

Answer 12

• Suitable for any gas, especially those soluble in water
• aka downward delivery of gas
• connect the delivery tube to a test tube for the gas to be collected
• this method is used to called gases that are denser than air
• eg. Carbon dioxide, chlorine, hydrogen chloride

Question 13

Methods to collect gas - using a graduated gas syringe

Answer 13

• Gases can be collected in a gas syringe attached to a conical flask
• the volume can be measured at rtp

Question 14

Drying of gases

Answer 14

• A gas can be dried by passing it through a drying agent
• the choice of drying agents used will depend on the nature of the gas to be dried

Question 15

Nature of gases

Answer 15

1. Ammonia: alkaline
2. Carbon dioxide: acidic
3. Carbon monoxide: neutral
4. Chlorine: acidic
5. Hydrogen: neutral
6. Hydrogen chloride: acidic
7. Nitrogen: neutral
   8: nitrogen dioxide: acidic
8. Oxygen: neutral
9. Sulfur dioxide: acidic
10. Sulfur trioxide: acidic

Question 16

Drying agents - concentrated sulfuric acid

Answer 16

• for drying acidic and neutral gas
• the tube introducing the gas is immersed in the acid while the exiting tube is not
• an acidic drying agent such as concentrated sulfuric acid cannot be used to dry alkaline gases like ammonia

Question 17

Drying agents - fused calcium chloride

Answer 17

• For drying acidic and neutral gas
• fused calcium chloride refers to calcium chloride that has been heated to remove all traces of water
• calcium chloride will react with ammonia gas and hence cannot be used to dry ammonia

Question 18

Drying agents - calcium oxide (quicklime)

Answer 18

• For drying alkaline gas
• a basic drying agent such as calcium oxide cannot be used to dry acidic gases like chlorine and carbon dioxide