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Measurements in Chemistry

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Presentation on theme: "Measurements in Chemistry"— Presentation transcript:

1 Measurements in Chemistry
Science in Focus, Chemistry O’Level, 2nd Edition, Chapter 1

2 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.

3 Apparatus for Measurement
Stopwatch measures time Accuracy: Nearest second Electronic balance measures mass Accuracy: Up to g Triple beam balance measures mass Accuracy: Nearest 0.1g

4 Apparatus for Measurement
Thermometer measures temperature Accuracy: Nearest 0.5 oC (either end with .0 or .5 oC) Gas Syringe measures volume of gas produced Accuracy: Nearest 1 cm3

5 Apparatus for Measurement
Measuring Volume of Solution Measuring Cylinder Holds either 100 or 250 cm3 Accuracy: Nearest 1 cm3 Burette Holds 50 cm3 Accuracy: Nearest 0.1 cm3 Pipette Holds 10.0, 20.0 or 25.0 cm3 Only measures fixed volumes.

6 Apparatus for Measurement
Is it correct to record a thermometer reading of 24.7 oC? What apparatus can we use to measure 80 cm3 of solution? What apparatus can we use to add 20.0 cm3 of acid solution drop by drop to an alkali solution? What apparatus can we use to measure out 22.4 cm3 of solution? wrong, because the thermometer can only record up to the nearest 0.5 oC Measuring cylinder Burette

7 Apparatus for Experiments
Heating of a Flammable Liquid Flammable liquid is heated using a water – bath. It can be used to find the boiling point of the flammable liquid. (Learn how to draw) If the boiling point of the liquid is higher than water, then we use oil instead of water (oil-bath).

8 Apparatus for Experiments
Titration 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. (Important when you learn acid and base calculations)

9 Apparatus for Experiments
Change 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.

10 Apparatus for Experiments
Volume 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.

11 Apparatus for Experiments
Stopper What are the two changes you would make to this set-up if you want to warm the flammable liquid? Explain. Heat Flammable liquid 1. Remove the stopper. This is to prevent pressure from building up in the tube and bursting the boiling tube. 2. Use a water-bath. This is to prevent the flammable liquid from catching fire as it is heated directly over a flame.

12 Volumetric flask To measure fixed volume of large amount of liquid
accurately. (accurate to 0.1 ml) e.g ml, ml

13 Apparatus for Experiments
Collection 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.

14 Apparatus for Experiments
Displacement of water (Learn how to draw) For gases insoluble in water, eg. oxygen, hydrogen, carbon dioxide

15 Delivery tube Gas Gas jar

16 Apparatus for Experiments
Upward delivery For gases soluble in water and less dense than air, eg. ammonia Special note: hydrogen (Learn how to draw)

17 Delivery tube Gas jar Gas

18 Apparatus for Experiments
Downward delivery For gases soluble in water and denser than air, eg. chlorine, hydrogen chloride, sulfur dioxide Special note: carbon dioxide (Learn how to draw)

19 Delivery tube Gas jar Gas

20 Apparatus for Experiments
Drying of gases (Removing water)

21 Apparatus for Experiments
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. What is the use of the water tank? What is the use of concentrated sulfuric acid? What gas is collected at the end? Explain. 1a. Water tank is to remove the soluble chlorine. b. Concentrated sulfuric acid is to remove water from the remaining gases and dry them. c. Carbon dioxide is collected because it is denser than air. Hydrogen escapes as it is less dense than air.

22 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

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