How close the atoms or molecules are to each other NOT really “heaviness” - density includes how much space an object takes up!! All matter has density including liquids, solids, and gases Again, density is the measure of the “compactness” of a material 1 Sponge and compacted bread in large flask of water or alcohol demo
“Compactness” or how ‘squeezed’ together 2 Low density not compact High density: compact
Density can also just compares the mass of an object to its volume So we can say it represents how compressed or squeezed the matter is together. This is a ratio d = mass = g or g Mass usually expressed in grams OR kg Volume usually expressed in cm 3 or liters, etc. Note: 1 mL = 1 cm 3 and 1L = 1000 cm 3 volume mL cm 3 DENSITY ! 3
Density Density is the ratio of mass to volume If the volume stays the same and the mass increases... 5g/2cm 3 = 10g/2cm 3 = the density will increase since top number is larger If the mass stays the same and the volume increases... 5g/2cm 3 = 5g/5cm 3 = The density will decrease since the bottom number is larger. 2.5 g/cm 3 5 g/cm g/cm 3 1 g/cm 3 4 5g 10 g 5g sity-and-buoyancy/density_en.html sity-and-buoyancy/density_en.html
Here are some simple rules. 1. For any equation/formula both sides of the = sign must stay equal. 2. Whatever you do on one side of the = sign you MUST do on the other. 3. Whatever function x + ÷-is being applied to the variable you must do the opposite to get rid of it. X is the opposite of ÷; + is the opposite of - Lets solve for the 3 variables in density. Algebra!: Chem’s best friend. 5
Lets solve for the 3 variables in density. Algebra!: Chem’s best friend. 6
DETERMINING DENSITY Regular Shapes – mass, then determine the volume by formula EX: cubes, cylinders, spheres, cones, etc. Irregular shapes – get mass, then measure displacement of a liquid (usually water) by that irregularly shaped object 1.Use a graduated cylinder, the smallest that will fit. 2.Add water to a any level & write down 3.Gently slide in the irregular object. 4.Read the new cylinder level, record. 5.Subtract the first water level from the second – this is the volume 6.Use the formula d=m/v 7.Divide your mass g by vol ml (cm 3 ) 7
Balloon and liquid nitrogen astr.gsu.edu/hbase/thermo/balloon.html#c1 astr.gsu.edu/hbase/thermo/balloon.html#c
LIQUIDS The more dissolved solids in a solution, the more dense the solution (such as ocean water) Cold water in lakes tend to sink (this creates a constant mixing of water, nutrients, and other substances) Alcohol/Water Demo less dense layers….. To Denser layers 9
What would happen???? Mercury density = 13600kg/m 3 (13.6g/cm 3 ) Lead density = 11340kg/m 3 (11.3g/cm 3 ) 10
Lead floats on liquid mercury! (so does this pool ball) 11
Archimedes and the Kings Crown s/2007/07/18/archimedes.jpg 12
SOLIDS Ice is less dense than water (which is why lakes and ponds have a thin layer of ice covering in winter, with water underneath) Rocks, woods, metals, everything really MUST have its own specific density This can be used to identify things! Wouldn’t you like to have a bunch of THIS dense material? 13
Solids Ice vs. water….. So ice is… LESS DENSE 14
Factors affecting Density Temperature Pressure 15 Which is high temperature, which is low? Low density High density High Temp Low temp Low pressure High pressure
Factors affecting Density Dissolved solids – in liquids Concentration and substance dissolved Which is more dense salt or fresh water? 16
FACTORS AFFECTING DENSITY ATomS!!!! Metals typically have the highest density. Uranium is denser than lead. Depleted uranium used to be in ‘tank ‘buster’ missiles. 17
How do you predict sinking or floating? (gas demo) SINK or FLOAT In Water Float Sink Float (alcohol) (fuel) 18 If the density is greater than the substance you put it in… It sinks If density is less than the substance… It floats! Density Challenge This trillion ton carrier floats because overall, it is less dense than water. HOW? The steel shell has many air ballasts so a lot of the volume is air which is far less dense than water and steel.