Presentation on theme: "SCIENTIFIC MEASUREMENT"— Presentation transcript:
1SCIENTIFIC MEASUREMENT To calculate Density, you have to know how to measure volume and mass properly and accurately!
2Reporting Measurements Using significant figuresReport what is known with certaintyAdd 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
3The instrument determines the amount of precision of the data. 62.4.00gWhat is the certain measurement here?What is the estimated measurement here?
4Using Significant Figures reflects precision by estimating the last digit 52 ml.8 mlWhat is the certain measurement?What is the estimated measurement?
5Measurements in the Lab: Example BExample A40 mL30 mL20 mL20 mL30 mL10 mLGraduated Cylinder marked in 1.0 mL increments. you record volume as mL1. If the glassware is marked every 10 mLs, as is this beaker, the volume you record should be in whole mLs. (Example A)2. If the glassware is marked every 1 mL, as is this graduated cylinder, the volume you record should be in tenths of mLs. (Example B)3. If the glassware is marked every 0.1 mL, as is this buret, the volume you record should be in hundredths of mLs. (Example C)Beaker marked in 10 mL increments.The volume you write in your lab report should be 13 mL0 mL1 mL2 mLExample CBuret marked in 0.1 mL increments. You record volume as 0.67 mL
6Practice Measuring cm 1 2 3 4 5 4.5 cm cm 1 2 3 4 5 4.54 cm cm 1 2 3 4 123454.5 cmcm123454.54 cmPRACTICE MEASURINGEstimate one digit of uncertainty.a) 4.5 cmb) * 4.55 cmc) 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 estimatecm123453.0 cmTimberlake, Chemistry 7th Edition, page 7
27DENSITYDensity is defined as mass per unit volume. It is a measure of how tightly packed and how heavy the atoms are in an object. Density is the ratio of mass to volumeYou can think of Density as the amount of stuff per unit of spaceDensity is the amount of matter within a certain volume.
28Density is the measure of the “compactness” of a material How close the atoms or molecules are to each other.More than “heaviness” - density includes how much space an object takes up!!All substances have density including liquids, solids, and gases.We need to be able to think about density visually, logically and mathematicallyBread slice and compacted bread in large flask of water
29Visually - Which one is more dense? Demonstration: Atoms in a substanceWhich square is more dense? circle oneMasses are / are not equalVolumes are / are not equal
30Visually - Which one is more dense? Now… which one is more dense?Masses are / are not equalVolumes are / are not equal
31Logically - What would take up more space. A kilogram of feathers… Logically - What would take up more space? A kilogram of feathers….. or a kilogram of steel?ROCKS - pass aroundOR
32DENSITY Mathematically Even though it has a numeric value, Density is a considered a (qualitative) intensive property of matter.does NOT depend on the quantity of matter.this is similar to temperatureContrast with (quantitative) extensive propertydepends on quantity of matter.mass and volume are quantitative.StyrofoamBrick
33Mathematically DETERMINING DENSITY Regular Shapes – mass, then determine the volume by formula/equationEX: cubes, rectangular prisms, cylinders, spheres, cones, etc.Irregular shapes – mass, then measure displacement of a liquid (usually water) by that irregularly shaped objectSince we know that 1 mL has the same volume as 1 cm3, we can make an easy conversion!Density = mass (g) volume (cm3 or mL)
34Equation to Calculate a Substance’s DENSITY For our terms and purposes:Mass is usually expressed in gramsVolume usually expressed in cubic centimeters (cm3) or milliliters (mL)Density may be expressed in other units, but you will learn about them in Physics and Chem….
35DENSITY - an important and useful (qualitative) intensive physical property AluminumPlatinumMercury13.6 g/cm321.5 g/cm32.7 g/cm3
36Density Calculations of: Regularly Shaped Solids:mass = triple beam or electronic balancevolume = measure (l x w x h)2. Irregularly Shaped Solids:volume = water displacement
37Density Calculations of: 3. Liquids: mass = tare graduated cylinder, mass liquid volume = read graduated cylinder We will perform labs on all of these types of density calculations!
38Learning Check – Mathematical Calculations of Density Osmium is a very dense metal. What is its density in g/cm3 if g of the metal occupies a volume of 2.22 cm3? 1) 2.25 g/cm3 2) 22.5 g/cm3 3) 111 g/cm3
39Learning Check – Mathematical Calculations of Density Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass = g = volume 2.22 cm3 = g/cm3 = 22.5 g/cm3
40Learning Check – Mathematical Calculations of Density Which diagram represents the correct order of liquid layers in the cylinder? (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL) 1) 2) 3)WKVVWKWVK
41Learning Check – Mathematical Calculations of Density The density of octane, a component of gasoline, is g/mL. What is the mass, in kg, of 875 mL of octane?1) kg2) 614 kg3) 1.25 kg
42Learning Check – Mathematical Calculations of Density If blood has a density of 1.05 g/mL, how many liters of blood are donated if 575 g of blood are given? 1) L 2) 1.25 L 3) 1.83 L 4) 548 L
43Learning Check – Logical Thinking about Density Fact: Water has a density of 1.0 g/ml and mercury (Hg) has a density of 13.6 g/ml.Which is heavier, a quart of water or a quart of mercury?If we have equal volumes of two different substances, then the one with the greater density will have the greater mass.
44Which is heavier, a ton of feathers or a ton of bricks? NeitherFeathersWhich is larger?If two objects have the same mass, the one with the higher density will be smaller.
45Factors Affecting Density Write the relationship statements. Temperature –What substance is the exception to this rule?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 °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.
46Factors Affecting Density A solid solutes dissolved into liquid solutions – the density change depends on the concentration and kind of substances mixed together.Write the relationship statement:
47Factors Affecting Density Atomic mass – Different atoms have different atomic masses. Write the relationship statement.
48Applying What You’ve Learned – Let’s think about the Density of Water!
49Question #1: At what temperature is water most dense? Find this information on your ESRT’s! Hint: Look for a section about the Properties of Water…Question #2: Use this chart to explain why ice floats on water. Use data from the chart to support your answer!!!!Question #3: Use this chart to explain what happens to average sea level when the ocean’s average temperature increases.
50Density Table SINK or FLOAT In Water? (D = 1.0 g/mL) Float Float Float (alcohol)Float(fuel)
51Specific GravityThe density of a material or substance, relative to another substanceExpressed in a ratio: water = 1.0 g/cm3Water is the substance to which we compare other substancesAlso known as SPECIFIC GRAVITYSince we dived the density of any substance by 1.0 g/cm3, the specific gravity value is equal to the density of the substance.What are the units for specific gravity?Relative Liquid densities: Oil, colored water, and corn syrup in a graduated cylinder.An H2O ice cube floats in liquid H2O but sinks 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).