Density and its measurement

Density 1.What is density? 2.How do you measure density? 3.Measuring the densities of objects Why do some things float and some things sink?

Density is a measure of how much stuff (mass) is packed into a certain space. Look at the two metal blocks-they both have the same mass Why does the aluminium block take up more space?

Copper atoms are heavier than aluminium atoms So we need more Aluminium to make 1 kg of material

Which one is MORE dense? If each box has the same volume, and each ball has the same mass, which box would weigh more? Why?

Summary Density tells us how much stuff is packed into a certain space Density changes because either: The materials are different and the atoms have different masses The way the particles are arranged is different (more or less spread out)

The “DMV” Triangle for Volume, Mass, and Density M ÷ ÷ D X V Density = Mass Volume Volume = Mass Density Mass == Density x Volume

Mass is measured in Kilograms (kg) Volume is measured in Metres cubed (m 3) ) Density is measured inKg/m 3

Changing units From grams to kilograms divide by g kg

From cm 3 to m divide by 1,000, cm m 3

Examples: A block of lead has a mass of 44000kg and a volume of 4m 3. What is the density of lead?

An ‘empty’ bedroom measures 5m x 4m x 2.5m. If the density of air is 1.3 kg/m 3 what is the mass of air in the room?

A piece of anthracite has a volume of 15 cm 3 and a mass of 27g. What is its density in kg/m 3 ?

Density of a regular solid Find the mass of the object by putting it on the balance Find the volume by measuring the length of the three sides with a ruler and then calculating the volume (l x w x h) Calculate the density –remember to keep your units correct!

What is the resolution of the rulers in the picture?

What is the smallest change in mass that this balance could measure? If the mass of our object is several grams then this resolution is good enough

10 mL graduated cylinder volume is 6.62 mL 100 mL graduated cylinder volume is 52.7 mL Determination of Certain Digits

Correct: viewing the meniscus at eye level. Incorrect: viewing the meniscus from an angle. Viewing the Meniscus

Viewing the meniscus from an angle can lead to false readings of the volume.

Micrometer screw gauge

 3.24mm ×0.01 Answer=7.78mm =7.79mm

Measuring the density of a liquid zero burette Measuring cylinder A burette can be used to measure the volume of a liquid more accurately

Fill a burette with water and let it run into a beaker to remove the air bubbles Read and record the volume of water in the burette Find the mass of an empty beaker Allow some water from the burette to run into the beaker Record the reading on the burette Reweigh the beaker to find the mass of water Calculate the density of water

To fill a buret, close the stopcock at the bottom & use a funnel. You may need to lift the funnel slightly to allow the solution to flow freely into the buret. Filling A Buret

Check the tip of the buret for an air bubble. To remove an air bubble, tap the side of the buret tip while solution is flowing. Air Bubbles in the Buret Tip

Hold a buret reading card behind the buret. Move the card until you can easily see the meniscus. Read the buret from top to bottom. This buret reads 11.34mL Reading the Buret

Finding the density of an irregular solid-method 2 Find the mass of the solid using the balance Fill the Eureka can with water Lower the solid into the water Measure the displaced water volume in the measuring cylinder Fill a small beaker almost full with water Lower it into a large beaker-carefully top up the water Lower the solid into the water Pour the displaced water into a measuring cylinder and measure the volume or

DENSITY OF AN IRREGULAR SOLID Find the Mass of the solid on a balance. Find the Mass of the solid on a balance. Fill the Measuring Cylinder with Water to a known Volume. Fill the Measuring Cylinder with Water to a known Volume. Add the Object. Add the Object. Work out the Volume of Water that is displaced. Work out the Volume of Water that is displaced. Calculate the Density. Calculate the Density. 50 cm 3 80 cm 3 m = 360 g

Vernier Caliper lock fixed scale vernier scale jaws

Vernier Scale Main Scale

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