Presentation on theme: "Density Is a physical property of matter"— Presentation transcript:
1 Density Is a physical property of matter Every pure substance has its own densityIs important for the identification of a sample of matterIs an intensive property of matter
2 Density Density is defined as mass per unit volume. The relationship can be written mathematically as:ORunits: solids [ g / cm3 ]liquids[ g / mL]gases [ g / L]
3 Comparison of Densities Each cube represents a volume of 1.00 cm3. The mass of each sample increases while the volume remains constant.
4 Example:The sample of matter you have has a mass of 3.51 g and occupies a volume of 1.30 cm3.
5 EXAMPLE:You need to add 45.0 g of alcohol to a sample. It is difficult to weigh an exact mass of a liquid. It is much easier to measure an exact volume. Using the density of the alcohol (0.789 g/cm3), you can determine what volume you would need to add to your sample so that you would be adding only the 45.0 grams.= 57.0 mL in the correct number of sig figs
6 Determining the Volume In order to figure the density we need to determine the volume:For regularly shaped objects we use direct measurement:
7 Measuring Volume by Displacement Used for irregular shaped objectsSelect a graduated cylinder large enough to put the object inAdd water and accurately record the initial volume.
8 SLOWLY add the object to be measured: rubber stopperrockmetal cylinderRead the new level of the waterThe water will rise an amount equal to the volume of the object
11 Do the math 1 . Original reading of volume Final volume of water This will equal the volume of the object22.5 mL mL = 5.1 mL Therefore, the volume of the object by displacement is 5.1 mL
12 EXAMPLE:An irregularly shaped piece of quartz was place in a graduated cylinder containing mL of water. The volume of the ater rose to mL. What is the volume of the water?Final volume24.35 mLInitial volumemL= volume of solid3.90 mL
14 Which block is more dense? Green BlockMass= 25.4 gramsVolume=29.8 cubic cmD = 25.4 g ÷ 29.8 cm3 == .852 g/ cm3Which block is more dense?
15 CylinderRadius = 3.5cmLength = 7.25 cmMass = 32.3 gWhat is the volume?V = π X radius2 X heightπ = 3.14What is the density?
16 SphereDiameter = 7.0cmRadius = 3.5cmMass = 32.3 gWhat is the volume?V = 4/3 π X radius3π = 3.14What is the density?
17 Density Can also be used as a means of separating components of matter Ex: if 2 solids of a different density are mixed together, the solid with the greater density will gravitate to the bottomWhen a solid object is placed in a liquid that has a great density, the solid object will float.We will test this hypothesis in lab.
19 The Concept of Density for Liquids and Solids THE DENSITY CONCEPTThe picture illustrates a density gradient.Each item (solid or liquid) is arranged in the cylinder according to its density.The samples are arranged with the greater densities toward the bottom and the lowest density on the top.The Concept of Density for Liquids and Solids