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SCIENTIFIC MEASUREMENT

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Reporting Measurements Using significant figures Report what is known with certainty Add ONE digit of uncertainty (estimation) Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 46

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

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

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Measurements in the Lab: 20 mL 30 mL 10 mL 0 mL 1 mL 2 mL Example A Example B 40 mL 30 mL 20 mL Example C

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Practice Measuring 4.5 cm 4.54 cm 3.0 cm Timberlake, Chemistry 7 th Edition, page 7 cm

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Finding VOLUME

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What is VOLUME? The amount of space that a 3-dimensional object or substance takes up. Anything that exists is made of matter and therefore has volume…(takes up space)

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The OBJECTS

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Formula/Equation? Length = 6cm Volume = L xW x H

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Finding Volume Length = 6cm Height = 4cm Volume = L x W x H

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Finding Volume Length = 6cm Height = 4cm Width = 2cm Volume = L x W x H

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Finding Volume Volume = L x W x H Length = 6cm Height = 4cm Width = 2cm

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6 cm x 2 cm x 4 cm = 48 cm 3 Volume = L x W x H =

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So, the VOLUME (the amount of space that this 3 dimensional object takes up) is 48 cm 3

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The OBJECTS

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Find the VOLUME

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The METHOD – Finding Volume by Water Displacement -40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL

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1. Note the water level -40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL

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2. Place the object in liquid -40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL

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-40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL 3. Watch the object displace the water it is place into…

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4. Note difference in water level -40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL

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The water level changed 15mL We can say the rock displaced 15mL of water -40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL 35 mL -20 mL 15 mL

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But wait, it gets better! -40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL

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Volume of our rock…

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Density 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 volume You can think of Density as the amount of stuff per unit of space

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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 mathematically Density is the measure of the compactness of a material

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Visually - Which one is more dense? Demonstration: Atoms in a substance Which square is more dense? circle one Masses are / are not equal Volumes are / are not equal

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Visually - Which one is more dense? Now… which one is more dense? Masses are / are not equal Volumes are / are not equal

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

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DENSITY 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 temperature Contrast with (quantitative) extensive property – depends on quantity of matter. – mass and volume are quantitative. StyrofoamBrick

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Mathematically DETERMINING DENSITY Regular Shapes – mass, then determine the volume by formula/equation EX: cubes, rectangular prisms, cylinders, spheres, cones, etc. Irregular shapes – mass, then measure displacement of a liquid (usually water) by that irregularly shaped object Since we know that 1 mL has the same volume as 1 cm 3, we can make an easy conversion! Density = mass (g) volume (cm 3 or mL)

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Equation to Calculate a Substances DENSITY For our terms and purposes: Mass is usually expressed in grams Volume usually expressed in cubic centimeters (cm 3 ) or milliliters (mL) Density may be expressed in other units, but you will learn about them in Physics and Chem….

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DENSITY - an important and useful (qualitative) intensive physical property Mercury 13.6 g/cm g/cm 3 Aluminum 2.7 g/cm 3 Platinum

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Density Calculations of: 1.Regularly Shaped Solids: mass = triple beam or electronic balance volume = measure (l x w x h) 2. Irregularly Shaped Solids: mass = triple beam or electronic balance volume = water displacement

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Density 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!

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Osmium is a very dense metal. What is its density in g/cm 3 if g of the metal occupies a volume of 2.22 cm 3 ? 1) 2.25 g/cm 3 2)22.5 g/cm 3 3)111 g/cm 3 Learning Check – Mathematical Calculations of Density

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Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass = g = volume2.22 cm 3 volume2.22 cm 3 = g/cm 3 = 22.5 g/cm 3 = g/cm 3 = 22.5 g/cm 3 Learning Check – Mathematical Calculations of Density

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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) K K W W W V V K Learning Check – Mathematical Calculations of Density V

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The density of octane, a component of gasoline, is g/mL. What is the mass, in kg, of 875 mL of octane? 1) kg 2) 614 kg 3) 1.25 kg Learning Check – Mathematical Calculations of Density

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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 4) 548 L

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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. Fact: Water has a density of 1.0 g/ml and mercury (Hg) has a density of 13.6 g/ml. Learning Check – Logical Thinking about Density

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Which is heavier, a ton of feathers or a ton of bricks? Which is larger? If two objects have the same mass, the one with the higher density will be smaller. Neither Feathers

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Factors Affecting Density Write the relationship statements. Temperature – What substance is the exception to this rule? Pressure –

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Factors 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:

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Factors Affecting Density Atomic mass – Different atoms have different atomic masses. Write the relationship statement.

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Applying What Youve Learned – Lets think about the Density of Water!

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Question #1: At what temperature is water most dense? Find this information on your ESRTs! 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 oceans average temperature increases.

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

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Specific Gravity The density of a material or substance, relative to another substance Expressed in a ratio: water = 1.0 g/cm 3 Water is the substance to which we compare other substances Also known as SPECIFIC GRAVITY Since we dived the density of any substance by 1.0 g/cm 3, the specific gravity value is equal to the density of the substance. What are the units for specific gravity?

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