Physical Properties and Density Turk

Physical Properties Viscosity Resistance to flow Decreases when a fluid is heated Conductivity Ability to allow heat to flow Malleability Can be hammered and change shape without shattering Hardness Melting and Boiling points

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

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

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

Lead floats on liquid mercury!

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

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) Example B Example A 0 mL 30 mL 20 mL 1 mL 10 mL 30-mL beaker: the volume you write in your lab report should be 13 mL 2 mL Buret marked in 0.1 mL: you record volume as 0.67 mL

Practice Measuring cm 1 2 3 4 5 4.5 cm cm 1 2 3 4 5 3.0 cm 1 2 3 4 5 4.5 cm cm 1 2 3 4 5 3.0 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 Timberlake, Chemistry 7th Edition, page 7

Using Significant Figures reflects precision by estimating the last digit 52 ml .8 ml What is the certain measurement? What is the estimated measurement?

The instrument determines the amount of precision of the data. 62.4 .00g What is the certain measurement here? What is the estimated measurement here?

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

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).

Absolute DENSITY The density of a material in its closest “packed form” For water: Absolute Density = 1000kg/m3 at 40C and 1 atm(pressure) in other words, the greatest density of water is at 40C

DETERMINING DENSITY 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)