Measurements in ChemistryScience in Focus, Chemistry O’Level, 2nd

Edition, Chapter 1

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What are we going to learn this Chapter?

Name appropriate apparatus for the measurement of time, temperature, mass and volume.

State the level of accuracy needed when using common measuring apparatus.

Suggest suitable apparatus for simple experiments

State the purpose of data logging and list examples of its uses.

Apparatus for Measurement

Stopwatch measures timeAccuracy: Nearest second

Electronic balance measures massAccuracy: Up to 0.001 g

Triple beam balance measures massAccuracy: Nearest 0.1g

Apparatus for Measurement

Thermometer measures temperatureAccuracy: Nearest 0.5 oC(either end with .0 or .5 oC)

Gas Syringemeasures volume of gas producedAccuracy: Nearest 1 cm3

Apparatus for Measurement

MeasuringCylinder Holds either 100 or 250 cm3

Accuracy: Nearest 1 cm3

Measuring Volume of Solution

BuretteHolds 50 cm3

Accuracy: Nearest 0.1 cm3

PipetteHolds 10.0, 20.0 or 25.0 cm3

Only measures fixed volumes.

Apparatus for Measurement

1. Is it correct to record a thermometer reading of 24.7 oC?

2. What apparatus can we use to measure 80 cm3 of solution?

3. What apparatus can we use to add 20.0 cm3 of acid solution drop by drop to an alkali solution?

4. What apparatus can we use to measure out 22.4 cm3 of solution?

Apparatus for Experiments

Flammable liquid is heated using a water – bath.

Heating of a Flammable Liquid

It can be used to find the boiling point of the flammable liquid.

If the boiling point of the liquid is higher than water, then we use oil instead of water (oil-bath).

(Learn how to draw)

Apparatus for Experiments

Use a sulfuric acid of known concentration. Pipette a fixed volume of it.

Add alkali solution bit by bit to it and find the volume needed to neutralized the acid completely

Use the alkali volume measured to neutralize the acid and find the concentration of the alkali.

Titration

(Important when you learn acid and base calculations)

Apparatus for ExperimentsChange in Mass during a Reaction

Used when gas is produced during a reaction.

As gas escapes, the mass of the substances in the flask decreases.

By measuring how fast the mass decreases, the speed of the reaction is determined.

Apparatus for ExperimentsVolume of Gas during a Reaction

Used when gas is produced during a reaction.

As gas escapes, it fills the space in the gas syringe.

By measuring how fast the syringe is filled, the speed of the reaction is determined.

Apparatus for Experiments

What are the two changes you would make to this set-up if you want to warm the flammable liquid? Explain.

Heat

Flammable liquid

Stopper

12

Volumetric flaskTo measure fixed volume of large amount of liquid accurately.(accurate to 0.1 ml)e.g. 100.0 ml, 250.0 ml

Apparatus for ExperimentsCollection of Gas

• Gases are collected for industrial and experimental uses after they are prepared.

• Common gases are hydrogen, oxygen, ammonia, chlorine and carbon dioxide.

• The method chosen to collect them depends on their solubility in water and density compared to air.

Apparatus for ExperimentsDisplacement of water

For gases insoluble in water, eg. oxygen, hydrogen, carbon dioxide

(Learn how to draw)

Delivery tubeGas

GasGas jar

Apparatus for Experiments

For gases soluble in water and less dense than air, eg. ammonia

Upward delivery

Special note: hydrogen

(Learn how to draw)

Delivery tubeGas jar

Gas

Gas

Apparatus for ExperimentsDownward delivery

For gases soluble in water and denser than air, eg. chlorine, hydrogen chloride, sulfur dioxide

Special note: carbon dioxide

(Learn how to draw)

Delivery tube

Gas jar

Gas

Gas

Apparatus for ExperimentsDrying of gases (Removing water)

1. Hydrogen, carbon dioxide, ammonia and chlorine are produced from a factory. They are passed through a water tank and then concentrated sulfuric acid and lastly collected by downward delivery.

a. What is the use of the water tank? b. What is the use of concentrated sulfuric acid? c. What gas is collected at the end? Explain.

Apparatus for Experiments

Data logging is used for• Temperature changes• Change in volume of gas produced• Change in mass during reaction • Change in pH as acid reacts with alkali

Apparatus for Experiments