Presentation on theme: "Measurements in Chemistry"— Presentation transcript:
1Measurements in Chemistry Science in Focus, Chemistry O’Level, 2nd Edition, Chapter 1
2What 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 experimentsState the purpose of data logging and list examples of its uses.
3Apparatus for Measurement Stopwatch measures timeAccuracy: Nearest secondElectronic balance measures massAccuracy: Up to gTriple beam balance measures massAccuracy: Nearest 0.1g
4Apparatus for Measurement Thermometermeasures temperatureAccuracy: Nearest 0.5 oC(either end with .0 or .5 oC)Gas Syringemeasures volume of gas producedAccuracy: Nearest 1 cm3
5Apparatus for Measurement Measuring Volume of SolutionMeasuringCylinderHolds either 100 or 250 cm3Accuracy: Nearest 1 cm3BuretteHolds 50 cm3Accuracy: Nearest 0.1 cm3PipetteHolds 10.0, 20.0 or 25.0 cm3Only measures fixed volumes.
6Apparatus 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 oCMeasuring cylinderBurette
7Apparatus for Experiments Heating of a Flammable LiquidFlammable 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).
8Apparatus for Experiments TitrationUse 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 completelyUse the alkali volume measured to neutralize the acid and find the concentration of the alkali.(Important when you learn acid and base calculations)
9Apparatus for Experiments Change in Mass during a ReactionUsed 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.
10Apparatus for Experiments Volume of Gas during a ReactionUsed 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.
11Apparatus for Experiments StopperWhat are the two changes you would make to this set-up if you want to warm the flammable liquid?Explain.HeatFlammable liquid1. 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.
12Volumetric flask To measure fixed volume of large amount of liquid accurately.(accurate to 0.1 ml)e.g ml, ml
13Apparatus for Experiments Collection of GasGases 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.
14Apparatus for Experiments Displacement of water(Learn how to draw)For gases insoluble in water, eg. oxygen, hydrogen, carbon dioxide
20Apparatus for Experiments Drying of gases (Removing water)
21Apparatus 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.
22Apparatus for Experiments Data logging is used forTemperature changesChange in volume of gas producedChange in mass during reactionChange in pH as acid reacts with alkali