DENSITY D = m/v (g/cm3) Mass usually expressed in grams Volume usually expressed in cm3 or liters, etc.

Density = amount of matter per unit volume Density is the ratio of mass to volume If the volume stays the same and the mass increases . . . the density will increase If the mass stays the same and the volume increases . . . The density will decrease

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

What would take up more space. A kilogram of feathers… What would take up more space??? A kilogram of feathers….. or a kilogram of steel?? ROCKS - pass around OR

Density is the measure of the “compactness” of a material How close the atoms or molecules are to eachother More than “heaviness” - density includes how much space an object takes up!! All substances have density including liquids, solids, and gases Bread slice and compacted bread in large flask of water

“Compactness” Hot air balloon - Describe how a hot air balloon works. Defend your argument.

SCIENTIFIC MEASUREMENT To calculate Density, you have to know how to properly measure!

Buret marked in 0.1 mL: you record volume as 0.67 mL Measurements in the Lab: Example B Example A 1. If the glassware is marked every 10 mLs, the volume you record should be in mLs. (Example A) 2. If the glassware is marked every 1 mL, the volume you record should be in tenths of mLs. 3. If the glassware is marked every 0.1 mL, the volume you record should be in hundredths of mLs. (Example B) 0 mL 30 mL 20 mL 1 mL 10 mL 30-mL beaker: Record volume as 13 mL 2 mL Buret marked in 0.1 mL: you record volume as 0.67 mL

Reporting Measurements Using significant figures Report what is known with certainty Add ONE digit of uncertainty (estimation) By adding additional numbers to a measurement – you do not make it more precise. The instrument determines how precise it can make a measurement. Remember, you can only add ONE digit of uncertainty to a measurement. Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 46

Practice Measuring cm 1 2 3 4 5 4.5 cm cm 1 2 3 4 5 4.54 cm cm 1 2 3 4 1 2 3 4 5 4.5 cm cm 1 2 3 4 5 4.54 cm PRACTICE MEASURING Estimate one digit of uncertainty. a) 4.5 cm b) * 4.55 cm c) 3.0 cm *4.550 cm is INCORRECT while 4.52 cm or 4.58 cm are CORRECT (although the estimate is poor) The better marks the better we can estimate. Scientist always understand that the last number measured is actually an estimate cm 1 2 3 4 5 3.0 cm Timberlake, Chemistry 7th Edition, page 7

Gases How much kinetic energy do the molecules have?? The greater the kinetic energy ……the greater the volume …… and the less dense that gas is!! Therefore, cold air is more dense than warm air

Low pressure weather system means warmer air tends to rise, High pressure systems indicate a colder more dense air mass that will……. SINK!!!

LIQUIDS The more dissolved solids in a solution, the more dense (such as ocean water) Cold water in lakes tend to sink (this creates a constant mixing of water, nutrients, and other substances) Kinetic energy again!! Straw solute Denser layers to less dense layers…..

What would happen???? Mercury density = 13600kg/m3 Lead density = 11340kg/m3 Sinking vial - make it float

Lead floats on liquid mercury!

Solids Ice vs. water…..

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) Various rocks, woods, metals have a characteristic density specific to that substance Beans/ping pong ball; Big jug of water in a pool Wouldn’t you like to have a bunch of THIS dense material?

Archimedes and the Kings Crown http://3quarksdaily.blogs.com/3quarksdaily/images/2007/07/18/archimedes.jpg 250 b.c., the Greek mathematician Archimedes - story

Factors affecting Density Temperature Pressure Add several drops of red food color to each of two 250-mL Erlenmeyer flasks; fill them with warm tap water. (If tap water is not warm, heat some tap water on a hot plate to 40-45 °C.) Add several drops of blue food coloring to each of the other two 250-mL Erlenmeyer flasks; fill them with cool tap water. Predict the outcome when one flask is inverted over the other. Place a paper card on top of the vessel filled with warm water. Invert the flask making sure to hold the card in place. Stack it on top of one of the cool water flasks. Remove the card. Remain prepared to catch the flasks.   ** Visual here. Place a paper card on top of the flask filled with cool water. Invert the flask making sure to hold the card in place. Stack it on top of the other warm water flask. Remove the card. Wide mouth containers may also be used.

Factors affecting Density Dissolved solids – in liquids Concentration and kind of substances

FACTORS AFFECTING DENSITY ATomS!!!! FACTORS AFFECTING DENSITY

Relative Density The density of a material or substance, relative to another substance Expressed in a ratio: water = 1g/cc Water is the substance to which we generally compare other substances ALSO known as SPECIFIC GRAVITY Relative Liquid densities: Oil, colored water, and corn syrup in a graduated cylinder. An H2O ice cube floats in liquid H2O but floats in rubbing alcohol. A can of diet coke floats in water while a can of regular coke sinks (can determine density of sugar versus NutraSweet using balance).

How are Submarines like fish…. The swim bladder in bony fish control their relative density in order to rise or dive in the water….buoyancy When air is added to the swim bladder, by diffusion through the blood vessels in the bladder walls, the fish becomes less dense overall when air is removed fish become more dense By changing the volume of air in the bladder, the fish’s density can be made equal to that of the surrounding water at a given depth. Air bladder when pulled up to quickly

DETERMINING DENSITY Use a graduated cylinder Regular Shapes – mass, then determine the volume by formula EX: cubes, cylinders, spheres, cones, etc. Irregular shapes – mass, then measure displacement of a liquid (usually water) by that irregularly shaped object Use a graduated cylinder Add water to a predetermined level - record. Gently drop in the irregularly shaped object. Read the graduated cylinder – record. Subtract the first water level from the second – this is the volume

Density Table SINK or FLOAT In Water (D = 1.0 g/mL) Float Float Float (alcohol) Float (fuel)