Measurement

Question 1

Measuring Mass

Answer 1

S.I unit: kilogram (kg)
other units: grams(g), tonne (t)=1000kg
Equipment: beam balance, electronic balance (acc:+- 0..01g or 2 dp), used for precise, fast weighting

Question 2

Measuring Time

Answer 2

S.I unit: second(s)
other units: minute (min), hour (h)
Equipment: stopwatch (digital, acc+-0.01s/ analogue, acc +-0.1s)

Question 3

Measuring Temp

Answer 3

S.I unit: kelvin(K)
other units: celsius (°c)
*Temp in K= Temp in °c +273
Equipment: mercury thermometer, alcohol thermometer (acc +-0.5°c), temp sensor connect to data logger–accurate readings than alcohol/mercury thermometer
-Data logger used to record&study changing temp of substance being heated&cooled over period of time, usually outdoors

Question 4

Measuring volume

Answer 4

S.I unit: cubic metre (m3)

other units: cubic centimetre (cm3), cubic decimetre (dm3) 1dm3= 1000cm3, 1m3=1000dm3

Question 5

How do we measure volumes of liquids?

Answer 5

-diff apparatus, diff degrees of accuracy

Apparatus: Measuring cylinder, burette, pipette

Question 6

Measuring cylinder

Answer 6

-measures to nearest 0.5cm3, (e.g. 41.5cm3, 99.0cm3)

Question 7

Burette

Answer 7

• accurately meausres out vol of liquid to nearest 0.05cm3
• scale marked in 0.1cm3 divisions
• used to deliver diff vol of liquids ( 24.00cm3, 38.95cm3)

Question 8

Pipette

Answer 8

-accurately measures fixed vols of liquids (e.g. 20.0cm3, 25.0cm3)

Question 9

How do we read the volume of a liquid?

Answer 9

• when water/solution is placed in a container, forms curved surface called a meniscus
• align ur eyes to the liquid level
• smiley meniscus (read off scale at the bottom of meniscus )
• sad meniscus (read off scale at top of meniscus)

Question 10

How do we measure volume of gases?

Answer 10

• gas syringe used to measure to vol of gases
• measures max vol of 100cm3
  (a) at the start of experiment, plunger pushed in fully to expel any gas in syringe
  (b) as gas from external source (e.g. gas produced from a chemical reaction) enters syringe, it pushes the plunger outwards

Question 11

Methods of Collecting Gases

Answer 11

-depends on physical properties of gases
1. Solubility - how soluble the gas is in water
2. Density - how dense the gas is compared to air
3 methods:
-Displacement of water
- Downward Delivery
- Upward delivery

Question 12

Displacement of water

Answer 12

apparatus: delivery tube, gas jar, container, water
- suitable for collecting gases that are insoluble or slightly soluble in water
- e.g. CO2, O2, H2 can be collected by this method

Question 13

Downward delivery

Answer 13

• used to collect gases soluble in water, denser than air
• e.g. chlorine, hydrogen chloride
• collection of poisonous gas to be carried out in fume cupboard

Question 14

Upward delivery

Answer 14

• used to collect gas soluble in water, less dense that air

- e.g. ammonia

Question 15

Hydrogen (Solubility in water/ Density compared to air/ Method of collection)

Answer 15

not soluble, less dense, displacement of water

Question 16

Oxygen (Solubility in water/ Density compared to air/ Method of collection)

Answer 16

very slightly soluble, slightly denser, displacement of water

Question 17

Carbon dioxide (Solubility in water/ Density compared to air/ Method of collection)

Answer 17

slightly soluble, denser, displacement of water

Question 18

Chlorine (Solubility in water/ Density compared to air/ Method of collection)

Answer 18

soluble, denser, downward delivery

Question 19

Hydrogen chloride (Solubility in water/ Density compared to air/ Method of collection)

Answer 19

very soluble, denser, downward delivery

Question 20

Sulfur dioxide (Solubility in water/ Density compared to air/ Method of collection)

Answer 20

very soluble, denser, downward delivery

Question 21

Ammonia (Solubility in water/ Density compared to air/ Method of collection)

Answer 21

extremely soluble, less dense, upward delivery

Question 22

Drying a gas (3 drying agents)

Answer 22

• concentrated sulfuric acid
• quicklime (calcium oxide)
• fused calcium chloride

Question 23

Concentrated sulfuric acid

Answer 23

Apparatus: Bottle with two holes, once for entrance of moist gas, one for dry gas to exit. Tube at entrance immersed in the acid, exiting tube not immersed

• used to dry most gases e.g. chlorine, hydrogen chloride
• cannot be used to dry ammonia, reacts with ammonia

Question 24

Quicklime

Answer 24

• also known as calcium oxide

- used to dry ammonia

Question 25

Fused calcium chloride

Answer 25

• calcium oxide that has been heated to remove all traces of water
• can be used to dry most gases