1. Measurements In Chemistry
Chapter Two
Measurements In Chemistry

2. Measurements in Chemistry
Measurements answer questions such as
How Much?
How Long?
How Many?
Measurements have 2 parts:
___________ ______________

3. Measurements in Chemistry
Importance of Units
Job Offer: Annual Salary = 1,000,000.
Do you Accept or Reject?

4. Measurements in Chemistry
Systems of Measurement
English System
Common measurements
Pints, quarts, gallons, pounds, miles, etc.
Metric System
Units in the metric system consist of a _______ unit plus a _________ (factor of ____).

5. Measurements in Chemistry
Base Units in the Metric System
Length
____________
Volume
Mass
(measure of the total quantity of matter in an object)

6. Measurements in Chemistry cont’d
Fig. 2.2
Comparisons of the base metric system units of length, mass, and volume with common objects.
E.R. Degginger

7. Measurements in Chemistry cont’d
Table 2.1 Prefixes

8. Measurements in Chemistry cont’d
Fig. 2.1
Metric system units are becoming increasingly evident on highway signs.
David Frazier/Photo Researchers

9. Measurements in Chemistry cont’d
Fig. 2.3
A cube 10 cm on a side is equal to 1 L; a cube 1 cm on a side is equal to 1 mL.

10. Measurements in Chemistry cont’d
Fig. 2.4
The use of the concentration unit milligrams per deciliteris common in clinical laboratory reports dealing with the composition of human body fluids.

11. Measurements in Chemistry
CO 2.1
Measurements are made relative to a __________.
Measurements can never be __________; there is always some ______________.
© Richard Hamilton Smith/Corbis Outline

12. Measurements in Chemistry
Exact and Inexact Numbers
Exact numbers
Have no ________________ associated with them
They are known __________ because they are ________
Example: ____ inches = ___ foot
Inexact number
Have some _________________ associated with them
Example: all __________________

13. Measurements in Chemistry
Uncertainty in Measurements depends upon the ___________________ device.
All numbers you “________” (_________) from the marks on the measuring device plus _____ “____________” or “____________________” number (decimal place)

14. Measurements in Chemistry cont’d
Fig 2.5
The scale on a measuring device determines the magnitude of the uncertainty for the recorded measurement.
Ruler A:
3.7 contains _____ significant digits
Ruler B:
3.74 contains _____ significant digits

15. Measurements in Chemistry cont’d
CAG

16. Measurements in Chemistry
Practice: Significant Figures
How many significant figures are in the following numbers?

17. Measurements in Chemistry cont’d
Fig. 2.6
The digital readout on an electronic calculator usually shows more digits than are needed.

18. Measurements in Chemistry
Rounding off Numbers
The number of significant figures in measurements affects any calculations done with these measurements
Your calculated answer can only be as certain as the numbers used in the calculation
Usually the calculator will show more significant digits than are needed
If the first digit to be deleted is _____ or less, simply drop it and all the following digits
If the first digit to be deleted is _____ or greater, that digit and all that follow are dropped and the last retained digit is increased by _____

19. Measurements in Chemistry
Practice: Rounding Off Numbers
Round the following to 3 significant figures
28.394
2568
2562

20. Measurements in Chemistry
Significant Figures and Calculations
Addition/Subtraction
Results are reported to the fewest decimal place
Perform the following calculations to the correct number of significant digits: =
= 6825.
= 6825
– =

21. Measurements in Chemistry
Significant Figures and Calculations
Multiplication/Division
Results are reported to the fewest number of significant figures
Perform the following calculations to the correct number of significant figures:
in x in =
cm2 / cm =
504 m x 230 m =

22. Measurements in Chemistry
Mixed Functions and Significant Figures
What is the result (to the correct number of significant figures) of the following calculations?
(23-21) x ( ) =
( ) x (322) =

23. Measurements in Chemistry
Scientific Notation must be used when magnitude of numbers are very large or very small.
Consider 1 drop of blood: 92% water by mass
There are 1,600,000,000,000,000,000,000 molecules of water each of which has a mass of gram.
1.6 x 1021 molecules of water
3.0 x g
__________ x ______________

24. Measurements in Chemistry
Scientific Notation
Shorthand for very large or very small numbers
In scientific notation you write a number in two parts:
The product of a number between one and ten (the coefficient) & an appropriate power of ten.
2.5 x 105
In scientific notation, the coefficient shows only the significant figures/digits.

25. Measurements in Chemistry
Exponents in Scientific Notation
The value of the exponent tells how many times to multiply or divide by 10
1 x 103 = 1 x 10 x 10 x 10 = 1000
1 x 10-3 = 1  10  10  10 = 0.001
Example: x Positive exponent means multiply by ten (23 times)
Example: 3 x 10-4
Negative exponent means divide by ten (4 times)

26. Measurements in Chemistry
Calculations in Scientific Notation
For Multiplication: ______________ Exponents
For Division: __________________ Exponents
For Addition and Subtraction all numbers must be expressed to the _________ exponential power.

27. Measurements in Chemistry
Calculations in Scientific Notation
The significant figures are those in the ___________
Usually, numbers in scientific notation will be multiplied or divided
Perform the following calculations:
(9.43 x 105) / (6.02 x 1023) =
(2.367 x 10-2) x (4.5 x 105) =
Make a note of how to enter scientific notation on your calculator:

28. Measurements in Chemistry
Additional Practice with Exponents.
(2.0 x 104) x (3.0 x 103) = 6.0 x 10
(8.8 x 107) / (2.0 x 105) = 17.6 x 10
(2.5 x 102) + (3.0 x 104)
(1.0 x 101) – (1.0 x 10-3)

29. Measurements in Chemistry
(2.5 x 102) + (3.0 x 104)

30. Measurements in Chemistry
(1.0 x 101) – (1.0 x 10-3)

31. Measurements in Chemistry
Conversion Factors
A conversion Factor is a ratio that specifies how one unit of measurement relates to another
Creating conversion factors from equalities
12 in.= 1 ft
I L = 1000 mL

32. Measurements in Chemistry cont’d
Fig. 2.7
It is experimentally determined that 1 inch equals 2.54 cm, or 1 cm equals inch

33. Measurements in Chemistry
1.00 cm = in
1.00 in = 2.54 cm

34. Measurements in Chemistry cont’d
Table 2.2

36. Measurements in Chemistry cont’d
CAG 2.1

37. Measurements in Chemistry
Dimensional Analysis
A problem solving method in which the units (associated with numbers) are used as a guide in setting up the calculations.
____________________

38. Measurements in Chemistry
The Steps of Dimensional Analysis
What is the ________? What do you want to ____ up with?
Write an = then write the information and unit you are _____ to start
3. Look for a _________ factor or chain of _______ that contain both the _____ you _______ with and the units you want in the _____
4. Multiply the ______ on the left by the conversion factor with the units you want on the ___ and the units you start with on the _______.
5. Make sure your units ______ out.

39. Measurements in Chemistry
Examples
Convert 180 pounds to kilograms
How many cups of water do you need for a recipe that calls for 3 pints? (1 pint = 2 cups)
Convert km to meters

40. Dimensional Analysis
Convert 180 pounds to kilograms

41. Dimensional Analysis
How many cups of water do you need for a recipe that calls for 3 pints? (1 pint = 2 cups)

42. Dimensional Analysis
Convert km to meters

43. Measurements in Chemistry
Examples
How many meters equal ft?

44. Dimensional Analysis
How many Liters equal 350 cubic inches?

45. A pediatric dosage of a certain antibiotic is 32 mg/kg of body weight per day. How much antibiotic, in milligrams per day, should be administered to a child who weighs 15.9 kg?

46. Measurements in Chemistry cont’d
Fig. 2.8
Both of these items have a mass of 23 grams, but they have very different volumes; therefore, their densities are different as well.

47. Measurements in Chemistry
What is Density?
A ratio of the ____ of an object divided by its ______
Typical units = ______ or ______
We have an unknown metal with a mass of g and a volume of cm3 What is its density?

48. Measurements in Chemistry cont’d
Table 2.3

49. Measurements in Chemistry cont’d
Fig. 2.9
The penny is less dense than the mercury it floats on.

50. Measurements in Chemistry
What does density have to do with what we have been talking about?
It’s a conversion factor!!!!!!
Examples:
What is the mass of 15 mL of Hg (mercury)? (d = g/mL)
You have been given 150 g of ethyl alcohol, which has a density of g/mL. How much volume does it take up? Will it fit into a 150 mL beaker?

51. Density
What is the mass of 15 mL of Hg (mercury)? (d = g/mL)

52. Density
You have been given 150 g of ethyl alcohol, which has a density of g/mL. How much volume does it take up? Will it fit into a 150 mL beaker?

53. Measurements in Chemistry cont’d
CC 2.1
The mass of a person is measured in both air and when submerged in water. These measurements are used to calculate a person’s density and percent body fat.

54. Measurements in Chemistry
Heat v. Temperature
Heat
A form of ____________
Always flows from objects with ______ temperature to objects of _____ temperature
Temperature
An indicator of the tendency of _____ energy to be transferred
A measure of how ____ or _____ an object is

55. Measurements in Chemistry cont’d
Fig 2.10
The relationships among the Celsius, Kelvin, and Fahrenheit temperature scales are determined by the degree sizes and the reference point values.

56. Measurements in Chemistry
Converting Between Temperature Scales
Conversions between Celsius and Kelvin
(temperature in K) = (temperature in oC) + 273
(temperature in oC) = (temperature in K) – 273
Conversions between Celsius and Fahrenheit
oF = 9/5 (oC) + 32
oC = 5/9(oF – 32)

57. Measurements in Chemistry
Heat Energy
Form of energy most often _________ or _________ by chemical reactions and physical changes
The calorie (cal) is a common ____ of energy, and is the amount of heat energy needed to raise the temperature of _______ of water by 1 _______ _________.
1 kilocalorie = _____ calories
The joule (J) is another unit for heat energy (q)
1 calorie = joules

58. Measurements in Chemistry
Specific heat (c):
Quantity of heat energy needed to raise the temperature of _______ of a substance by __________ Celsius
Units: J/goC or cal/goC
The higher the specific heat of a substance, the _____ its temperature will ________ when heat is added to it

59. Measurements in Chemistry cont’d
Table 2.4
Specific Heats of common substances

60. Measurements in Chemistry
The Effect of the High Specific Heat of Water
Moderate Climates – near large bodies of water with ability to absorb large amounts of heat without undergoing drastic temperature changes.

61. A horse trainer exercises a horse twice each day, every day, seven days each week. The horse is run 5 laps each morning and 5 laps each afternoon. The length of the race track is miles. Most horse races are measured in furlongs with exactly 8 furlongs equaling exactly one mile. How many furlongs does the horse run over a period of a fortnight (2 weeks)? Show all of your work for full credit. Hint: ? furlongs = 1 fortnight

62. A dump truck is designed to hold 5. 50 cubic yds (yd3)
A dump truck is designed to hold 5.50 cubic yds (yd3). What is this volume in cubic centimeters (cc or cm3)? Hint: 1 cubic yd measures exactly 3 ft or 36 inches on each side. Express you answer in proper scientific notation. (5 points) Show all of your work for full credit.