SCIENTIFIC MEASUREMENT

1. SCIENTIFIC MEASUREMENT To calculate Density, you have to know how to measure volume and mass properly and accurately!

2. 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

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

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

5. Measurements in the Lab: Example B Example A Graduated Cylinder marked in 1.0 mL increments. you record volume as 35.5 mL 1. 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) 0 mL 40 mL 30 mL Beaker marked in 10 mL increments. The volume you write in your lab report should be 13 mL 20 mL 30 mL 1 mL 10 mL Example C 2 mL 20 mL Buret marked in 0.1 mL increments. You record volume as 0.67 mL

6. 1 2 3 4 5 0 cm 1 2 3 4 5 0 cm 1 2 3 4 5 0 cm Practice Measuring 4.5 cm 4.54 cm 3.0 cm Timberlake, Chemistry 7th Edition, page 7

7. Finding VOLUME

8. Finding VOLUME 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)

9. The OBJECTS

10. The OBJECTS Let's try this one first!

11. Formula/Equation? Volume = L xWx H Length = 6cm

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

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

14. Finding Volume Volume = L x W x H Length = 6cm Width = 2cm Height = 4cm SO MULTIPLY 'EM!

15. Volume = L x W x H = 6cm x 2cm x 4cm = 48cm3

16. So, the VOLUME (the amount of space that this 3 dimensional object takes up) is 48 cm3 Nice work.

17. The OBJECTS Now, let's try this one

18. Find the VOLUME Can't do L x W x H… …it's an irregular shape. things that make you go hmmmm...

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

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

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

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

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

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

25. But wait, it gets better! 3 1mL = 1cm -40mL -35mL -30mL -25mL -20mL -15mL -10mL -5mL so... 3 15mL = 15cm

26. Volume of our rock… 3 = 15cm Great work!

27. DENSITY • 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

28. 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

29. 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

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

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

32. MathematicallyDETERMINING 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 cm3, we can make an easy conversion! Density = mass (g) volume (cm3 or mL)

33. Equation to Calculate a Substance’s DENSITY For our terms and purposes: • Mass is usually expressed in grams • Volume 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….

34. Platinum Mercury Aluminum DENSITY - an important and useful (qualitative) intensive physical property 13.6 g/cm3 21.5 g/cm3 2.7 g/cm3

35. Density Calculations of: • 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

36. 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! 

37. Learning Check – Mathematical Calculations of Density Osmium is a very dense metal. What is its density in g/cm3 if 50.00 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

38. Learning Check – Mathematical Calculations of Density Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass = 50.00 g = volume 2.22 cm3 = 22.522522 g/cm3 = 22.5 g/cm3

39. Learning 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) K W V V K W W V K

40. Learning Check – Mathematical Calculations of Density The density of octane, a component of gasoline, is 0.702 g/mL. What is the mass, in kg, of 875 mL of octane? 1) 0.614 kg 2) 614 kg 3) 1.25 kg

41. Learning 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) 0.548 L 2) 1.25 L 3) 1.83 L 4) 548 L

42. Learning 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.

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

44. Factors Affecting DensityWrite the relationship statements. • Temperature – What substance is the exception to this rule? • Pressure –

45. 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:

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

47. Applying What You’ve Learned – Let’s think about the Density of Water!

48. Question #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.

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

50. Specific Gravity • The density of a material or substance, relative to another substance • Expressed in a ratio: water = 1.0 g/cm3 • 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/cm3, the specific gravity value is equal to the density of the substance. • What are the units for specific gravity?