Physics. Practical 5: Density. Practical Objective. Content Objective. Apparatus. Your teacher may watch to see if you can:

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1 The density of a substance is the mass of a unit volume of that substance. Almost all substances are most dense when they are solids and least dense when they are gases. The arrangement of particles can explain the differences in density between different states of matter. A solid substance is usually more dense than the same substance as a liquid, because the particles in solids are closer together. The exception to this is water, where the liquid is more dense than the solid (ice). You will complete three experiments on density. You will determine the density of liquids and solid objects with both regular and irregular shapes. Your teacher may watch to see if you can: follow instructions carefully take careful measurements work safely. To identify a substance from its density. Density is mass per unit volume. solid objects/blocks with regular shapes 30 cm ruler Core learning outcomes: I am able to... use appropriate apparatus to make and record accurate measurements of length, area, mass and volume use such measurements to determine the density of solid objects and liquids. Task 1: To determine the density of regular shaped objects 1 Select four different regular shaped objects from the selection provided. If they have labels, write these in the first column of the table on the next page. Otherwise, write a brief description (e.g. black cube). 2 Measure all the dimensions (length, width and height) for each object to one decimal place using a 30 cm ruler. Record your results in centimetres in the table on the next page. 3 Measure the mass of each object in grams using a and record this in the table on the next page. 1

2 1 To calculate volume (column 6), multiply length (column 2) by width (column 3) by height (column 4). Volume = length width height 2 To calculate density (column 7), use the equation: Object Length Width Height Mass in g Volume 3 Density in g/cm 3 Material substance is made from 3 Use the table below to work out what each substance is and complete column 8. Substance Aluminium Brass Copper Iron Lead Wood Zinc Density in g/cm Compare your answers to the correct answers for each material. How well did you do? 2

3 Task 2: To determine the density of irregular shaped objects 1 Choose an object with an irregular shape from the selection provided and measure its mass using the. Write the name of the material and the mass of the object in the table below. Tie some thread or very thin string around the object. 2 Stand a on the bench with its spout over a bowl. Fill the can with water until the water just starts to come out of the spout. 3 When it has stopped dripping, hold a measuring cylinder under the spout and carefully lower the object into the can using the string. 4 Stand the measuring cylinder on the bench and read the volume of water you have collected. This is the same as the volume of your object. Record this volume in the table below. 5 Repeat steps 1 4 with four more objects with irregular shapes. measuring cylinder ml ml The volume of the water displaced by an object is the same as the volume of the object. To find the density of solid objects with irregular shapes. To calculate the density of solid objects with irregular shapes, the volume of the objects can be measured through displacement of a liquid medium. measuring cylinder bowl solid objects with irregular shapes thread or very thin string Safety! Mop up any spills straight away. 1 Complete the table below. Material Mass in g Volume 3 Density in g/cm 3 2 Calculate the density of each object and write it in the table. The equation you need is: 3

4 Task 3: Densities of liquids 1 Zero the. Place an empty measuring cylinder on the and record its mass. 2 Carefully pour 50 cm 3 of a liquid into the measuring cylinder. Write down the name of the liquid and the reading on the. Subtract the mass of the empty measuring cylinder from this reading to calculate the mass of 50 cm 3 of the liquid. 3 Repeat step 2 with four more liquids, washing your measuring cylinder each time before replacing the liquid. 1 Complete the table below. Liquid Mass of 50 cm 3 (g) Density (g/cm 3 ) To find the density of a liquid. Different concentrations of the same solute in solution will have differing densities. measuring cylinder beaker liquids, such as water and sugar or salt solutions of various concentrations Safety! Mop up any spills straight away. 2 Calculate the density of each liquid and write it in the table. The equation you need is: Considering your results/conclusions 3 a What was the range of densities for the solids you measured? b What was the range of densities for the liquids? 4 Compare the densities of the solids and liquids that you tested. 4

5 Exam-style questions 01 A student wants to calculate the density of the two objects shown. cube of metal pound coin 01.1 Describe the measurements that the student should take and how the student would use these measurements to calculate the densities of the two objects. You may wish to draw a small diagram to help your explanation of the pound coin. a Cube of metal [4 marks] b Pound coin [4 marks] 01.2 a Calculate the mass of a cube of length 3 cm if its density is 0.6 g/cm 3. Include an appropriate unit of mass. [3 marks] b Explain whether the cube will float or sink in water. [2 marks] c Calculate the density of the pound coin if its mass is 9.5 g and volume is 1.25 cm 3. Include an appropriate unit of density. [2 marks] 5