1. Scientific Measurement

2. What is Chemistry? Matter - anything that has mass and takes up space.
Chemistry - the study of the composition of matter and the changes that matter undergoes.
Involves all aspects of life b/c all living and nonliving things are made of matter

3. Five Areas of Chemistry
Organic – carbon chemistry
Inorganic – non-carbon chemistry; generally non-living things (ex. Rocks)
Biochemistry – processes in organisms (ex. Muscle contraction and digestion)
Analytical – composition of matter (ex. Measuring amount of Pb (lead) in H2O)
Physical – mechanisms, rate, and E transfer

4. Scientific Notation
Chemistry often deals with very large and very small numbers.
There are approximately 602,200,000,000,000,000,000,000 molecules of water in 18 mL
one electron has a mass of g
We need a shorter way of writing these numbers

5. Scientific Notation Consists of two parts 1. a number between 1 and 10
2. multiplied by 10 raised to a power
602,200,000,000,000,000,000,000 = x 1023
g = x 10-28

6. Putting a number into scientific notation
STEP 1 - Determine how many times you have to move the decimal place to make a number between 1 and 10
= 3.24

7. STEP 2 - Determining the exponent
The number of places you move the decimal becomes the exponent
Starting with a number greater than 1 = a positive exponent
Starting with a number less than 1 = a negative exponent
4.5 x 10-4

8. Going from scientific notation to a “regular” number
Move the decimal place as indicated by the exponent
Negative exponents give you numbers less than one. Positive exponents give you numbers greater than one

9. Examples
3.21 x 104
32100
6.17 x 10 -5

10. USING YOUR CALCULATOR EXP button
Adding, subtracting, multiplying, & dividing – USE PARENTHESES

11. PRACTICE

12. How good are the measurements?
Accuracy- how close the measurement is to the actual value
Precision- how well can the measurement be repeated

13. Differences
Accuracy can be true of an individual measurement or the average of several.
Precision requires several measurements before anything can be said about it.

14. Let’s use a golf anaolgy

15. Accurate? No
Precise?
Yes

16. Accurate?
Yes
Precise?
Yes

17. Precise? No
Accurate?
Maybe?

18. Accurate?
Yes
Precise?
We can't say!

19. In terms of measurement
Three students measure the room to be m, 10.2 m and 10.1 m across. The room is actually 10.5m across.
Were they precise?
Were they accurate?

20. Percent Error __| Experimental – Accepted |__ Accepted
Experimental – what you got
Accepted – what you should have gotten
Based on reliable references
Absolute value!

21. Percent Error Example
I measured a sample of a boiling liquid to be 79.1°C. The text says that water’s boiling point is 85°C. What is the percent error?

22. Significant Figures
In a measurement, all known digits plus one estimated digit are called significant figures or significant digits
AKA “sig figs”
Tells us about the accuracy of a measurement

23. Significant figures (sig figs)
When we measure something, we can (and do) always estimate between the smallest marks. 2 1 3 4 5

24. Significant figures (sig figs)
The better the marks, the better we can estimate.
Scientists always understand that the last number measured is actually an estimate. 1 2 3 4 5

25. Significant figures (sig figs)
The measurements we write down tells us about the instrument we use
The last digit is between the lines
What is the smallest mark on the ruler that measures cm?
141
142

26. Significant figures (sig figs)
What is the smallest mark on the ruler that measures 142 cm?
100
200
150
250 50

27. 140 cm?
100
200
150
250 50
100
200
There’s a problem – which ruler was used to measure 140 cm?

28. 140 cm?
100
200
150
250 50
100
200
Scientists needed a set of rules to help us know which zeroes are measured and which are estimates

29. RULES of SIG FIGS 1. Non zeros are ALWAYS significant.
46.3 = 3 sig figs = 3 sig figs
2. Zeroes between non zeroes ARE significant
40.7 = 3 sig figs = 4 sig figs

30. RULES of SIG FIGS
3. If there’s a decimal, start counting at the first NON-ZERO and count all the way to the end
0.045 = 2 sig figs
= 3 sig figs
1.200 = 4 sig figs
4.00 = 3 sig figs

31. RULES of SIG FIGS
4. If there’s NOT a decimal, ignore any zeroes at the end 270 = 2 sig figs = 2 sig figs = 2 sig figs

32. 140 cm?
100
200
150
250 50
100
200

33. Back to our ruler problem
140 has 2 significant figures
That tells us the measurement was only taken to the hundreds and the tens are estimated

34. 140 cm
100
200

35. Numbers without sig figs
Counted numbers
12 eggs in a dozen
32 students in a class
Definitions
1 m = 100 cm
16 ounces is 1 pound
AKA “Unlimited” significant figures

36. Scientific notation Only use first part!
How many sig figs in 1.20 x 103 m?

37. Sig figs. How many sig figs in the following measurements? 458 g

38. Significant Figures Rules for adding and subtracting
The answer should be rounded to the same number of decimal places as the measurement with the least number of decimal places.

39. For example
27.93
6.4 +
27.93
6.4 +
27.93
6.4
34.33

40. Multiplication and Division
Rules for multiplying and dividing
The answer should be rounded to the same number of sig figs as the measurement with the least number of sig figs.

41. Volume How much space an object occupies Graduated Cylinders
Come in variety of sizes
Measure in milliliters (mL) 50 40 30 20 10

42. How to Measure Volume 50
Meniscus - the curve the water takes in the cylinder 40 30
Measure at the bottom
of the meniscus. 20 10

43. How to Measure Volume
Always be level with the meniscus to avoid parallax errors
Incorrect: viewing the meniscus from an angle
Correct: Viewing the meniscus at eye level

44. How to Measure Volume
Read the volume using all certain digits and one uncertain digit.
Certain digits are determined from the calibration marks on the cylinder.
The uncertain digit (the last digit of the reading) is estimated.

45. How to Measure Volume Use the graduations to find all certain digits
There are two unlabeled graduations below the meniscus, and each graduation represents 1 mL, so the certain digits of the reading are…
52 mL.

46. How to Measure Volume Estimate the uncertain digit and take a reading
The meniscus is about eight tenths of the way to the next graduation, so the final digit in the reading is
0.8 mL
The volume in the graduated cylinder is
52.8 mL.

47. Measuring Temperature
0ºC
Measuring Temperature
Same as volume – read to the calibration marks and then estimate the last digit
Do not allow the thermometer to touch the walls or bottom of the beaker, etc. when measuring temperature

48. Reading the Thermometer
_ _ . _ C 8 7 4
_ _ . _ C 3 5

49. Mass Quantity of matter in an object WEIGHT – depends on gravity
Massing an object often called “weighing” b/c weight is proportional to mass

50. Measuring Mass
Analytical balance 3-beam balance

51. How to measure Mass
100
200
400
300
500 10 20 30 40 50 60 70 80 90 1 2 3 4 5 6 7 8 9 10

52. Measuring Mass
Always check that the balance is level and zeroed before using it.
Never weigh chemicals directly on the balance pan. Always use a weighing boat or a dish.
Do not weigh extremely hot or cold objects.

53. The Metric System

54. Measuring Numbers without units are meaningless. “It is 10 long.”
10 what?

55. The Metric System Easier to use b/c it’s a decimal system.
Every conversion is by some power of 10.
A metric unit has two parts - a prefix and a base unit.
Prefix tells you how many times to divide or multiply by 10.

57. The International System of Units (SI)
Most common base units
meter (m) - length
gram (g) – mass
Liter (L) – volume
Kelvin (K) – temperature
K = °C + 273
second (s) - time
mole (mol) – amount of substance

58. Common Metric Prefixes
Mega (M) = 106
** Kilo (k) = 103
** Deci (d) = 10-1
** Centi (c) = 10-2
** Milli (m) = 10-3
Micro (µ) = 10-6
Nano (n) = 10-9
Pico (p) = 10-12

59. Converting with a ladderk h D d c m
The box is the base unit (meters, Liters, grams, etc.)
Find your starting unit
Count the steps to your end unit.
The direction you move is the direction you move the decimal.

60. Conversions with a ladderk h D d c m
Change 5.6 m to millimeters
Starts at the base unit and moves three to the right.
So…move the decimal point three to the right 5 6

61. Conversions with a ladderk h D d c m
Convert 25 mg to grams
Convert 0.45 km to mm
Convert 35 mL to liters

62. Conversions with a ladder
Only works with same base unit
m to cm
kg to mg
So what do we do if the units are different or don’t use the decimal system?
Feet to inches
Meters to miles

63. Conversion factors A ratio of equivalent measurements. 1 m = 100 cm
Or write it as a ratio 1 m OR cm
100 cm m
Conversion factor is equal to 1

64. Dimensional Analysis
Easy way to convert units – even if it’s NOT a decimal system
Make sure your units cancel out
Calculate like a fraction

65. EXAMPLE 13 inches is how many yards? 36 inches = 1 yard
13 inches 1 yard = 13 = yards
36 inches

66. Dimensional Analysis
Really just multiplying by one, in a creative way.
Choose the conversion factor that gets rid of the unit you don’t want.

67. Dimensional Analysis
A ruler is 12.0 inches long. How long is it in cm? ( 1 inch is 2.54 cm)
in meters?
A race is 10.0 miles long. How far is this in yards?
1 mile = 1760 yards
Pikes Peak is 14,110 ft above sea level. What is this in meters?
1 meter = 3.28 feet

68. Multiple Units 25 kg = _____ mg 25 kg 1000 g 1 kg 1000 mg 1 g
25, 000, 000 mg = 2.5 x 10 7 mg

69. Multiple units The speed limit is 65 mi/hr. What is this in m/s?
1 mile = 1760 yds
1 meter = yds
65 mi hr
1760 yd
1 m
1 hr
1 min
1 mi
1.094 yd
60 min
60 s

70. Density The ratio of mass to volume D = m / V
Density is the same no matter the sample size so it can be used to help identify unknown substances

71. Calculating D = m/V Units will be g/mL or g/cm3 1 mL = 1 cm3
A piece of wood has a mass of 11.2 g and a volume of 23 mL. What is the density?

72. Calculating
A piece of wood has a density of 0.93 g/mL and a mass of 23 g. What is the volume?
Return to Algebra 1
What ever you do to one side, do to the other.
How would you find the density in kg/L?

73. m D V

74. Floating Lower (less) density floats on higher (more) density.
Ice is less dense than water (Atypical)
Most wood is less dense than water.
Helium is less dense than air.
A ship is less dense than water.