1. Welcome to the World of Chemistry

2. Types of Observations and Measurements
We make QUALITATIVE observations of reactions — changes in color and physical state.
We also make QUANTITATIVE MEASUREMENTS, which involve numbers.
Use SI units — based on the metric system

3. Can you hit the bull's-eye?
Three targets with three arrows each to shoot.
How do they compare?
Both accurate and precise
Precise but not accurate
Neither accurate nor precise
Can you define accuracy and precision?

4. How do you convert measurements using dimensional analysis?
Use a fraction as a conversion factor
By using dimensional analysis / factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!

5. How many minutes are in 2.5 hours?
Conversion factor
2.5 hr x min = min
1 hr
cancel
By using dimensional analysis / factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!

6. Steps to Problem Solving
Write down the given amount. Don’t forget the units!
Multiply by a fraction.
Use the fraction as a conversion factor. Determine if the top or the bottom should be the same unit as the given so that it will cancel.
Put a unit on the opposite side that will be the new unit. If you don’t know a conversion between those units directly, use one that you do know that is a step toward the one you want at the end.
Insert the numbers on the conversion so that the top and the bottom amounts are EQUAL, but in different units.
Multiply and divide the units (Cancel).
If the units are not the ones you want for your answer, make more conversions until you reach that point.
Multiply and divide the numbers. Don’t forget “Please Excuse My Dear Aunt Sally”! (order of operations)

7. Sample Problem
You have $7.25 in your pocket in quarters. How many quarters do you have?
7.25 dollars quarters
1 dollar
= 29 quarters X

8. You Try This One!
If Jacob stands on Spencer’s shoulders, they are two and a half yards high. How many feet is that?

9. How many seconds are in 1.4 days? Unit plan: days hr min seconds
Learning Check
How many seconds are in 1.4 days?
Unit plan: days hr min seconds
1.4 days x 24 hr x ??
1 day

10. Wait a minute!
What is wrong with the following setup?
1.4 day x 1 day x min x 60 sec
24 hr hr min

11. What is Scientific Notation?
Scientific notation is a way of expressing really big numbers or really small numbers.
For very large and very small numbers, scientific notation is more concise.

12. Scientific notation consists of two parts:
A number between 1 and 10
A power of 10
N x 10x

13. To change standard form to scientific notation…
Place the decimal point so that there is one non-zero digit to the left of the decimal point.
Count the number of decimal places the decimal point has “moved” from the original number. This will be the exponent on the 10.
If the original number was less than 1, then the exponent is negative. If the original number was greater than 1, then the exponent is positive.

14. Examples Given: 289,800,000 Use: 2.898 (moved 8 places)
Answer: x 108
Given:
Use: 5.67 (moved 4 places)
Answer: 5.67 x 10-4

15. To change scientific notation to standard form…
Simply move the decimal point to the right for positive exponent 10.
Move the decimal point to the left for negative exponent 10.
(Use zeros to fill in places.)

16. Example
Given: x 106
Answer: 5,093,000 (moved 6 places to the right)
Given: x 10-4
Answer: (moved 4 places to the left)

17. Learning Check Express these numbers in Scientific Notation: 405789 2

18. Addition or Subtraction with Scientific Notation
The exponents must be the same
Convert to same exponent then add or subtract number
2.45 x x 106 = ?
.245 x x 106 = x 106

19. Multiplication and Division with Scientific Notation
Multiply or divide the number then add or subtract the exponent
Convert to scientific notation
(5.60 x 1012 ) x (7.102 x 104 ) = ?
5.6×7.102 = 39.8
1012×104 = = (5.60×1012)×(7.102×104) = 39.8×1016
39.8×1016 = 3.98×1017

20. Chemistry In Action
On 9/23/99, $125,000,000 Mars Climate Orbiter entered Mars’ atmosphere 100 km lower than planned and was destroyed by heat.
1 lb = 1 N
1 lb = 4.45 N
“This is going to be the cautionary tale that will be embedded into introduction to the metric system in elementary school, high school, and college science courses till the end of time.”

21. Significant Figures
The numbers reported in a measurement are limited by the measuring tool
Significant figures in a measurement include the known digits plus one estimated digit

22. Counting Significant Figures
RULE 1. All non-zero digits in a measured number are significant. Only a zero could indicate that rounding occurred.
Number of Significant Figures
38.15 cm 4
5.6 ft 2
65.6 lb ___
m ___

23. Leading Zeros
RULE 2. Leading zeros in decimal numbers are NOT significant.
Number of Significant Figures
0.008 mm 1
oz 3
lb ____
mL ____

24. Sandwiched Zeros
RULE 3. Zeros between nonzero numbers are significant. (They can not be rounded unless they are on an end of a number.)
Number of Significant Figures
50.8 mm 3
2001 min 4
0.702 lb ____
m ____

25. Trailing Zeros 25,000 in. 2 200. yr 3 48,600 gal ____
RULE 4. Trailing zeros in numbers without decimals are NOT significant. They are only serving as place holders.
Number of Significant Figures
25,000 in. 2
200. yr 3
48,600 gal ____
25,005,000 g ____

26. Learning Check A. Which answers contain 3 significant figures?
1) ) ) 4760
B. All the zeros are significant in
1) ) ) x 103
C. 534,675 rounded to 3 significant figures is
1) ) 535, ) 5.35 x 105

27. Learning Check
In which set(s) do both numbers contain the same number of significant figures?
1) and 22.00
2) and 40
3) and 150,000

28. Learning Check
State the number of significant figures in each of the following:
A m
B L
C g
D m
E. 2,080,000 bees

29. Significant Numbers in Calculations
A calculated answer cannot be more precise than the measuring tool.
A calculated answer must match the least precise measurement.
Significant figures are needed for final answers from
1) adding or subtracting
2) multiplying or dividing

30. Adding and Subtracting
The answer has the same number of decimal places as the measurement with the fewest decimal places.
one decimal place
two decimal places
26.54
answer one decimal place

31. Learning Check
In each calculation, round the answer to the correct number of significant figures.
A =
1) ) ) 257
B =
1) ) ) 40.7

32. Multiplying and Dividing
Round (or add zeros) to the calculated answer until you have the same number of significant figures as the measurement with the fewest significant figures.

33. Learning Check
A X 4.2 =
1) ) )
B ÷ =
1) ) ) 60
C X =
X 0.060
1) ) )

34. Reading a Meterstick
. l I I I I cm
First digit (known) = ?? cm
Second digit (known) = ? cm
Third digit (estimated) between
Length reported = cm
or cm
or cm

35. Known + Estimated Digits
In 2.76 cm…
Known digits 2 and 7 are 100% certain
The third digit 6 is estimated (uncertain)
In the reported length, all three digits (2.76 cm) are significant including the estimated one

36. Learning Check . l8. . . . I . . . . I9. . . .I . . . . I10. . cm
What is the length of the line?
1) cm
2) cm
3) cm
How does your answer compare with your neighbor’s answer? Why or why not?

37. Zero as a Measured Number
. l I I I I cm
What is the length of the line?
First digit ?? cm
Second digit ? cm
Last (estimated) digit is cm

38. Always estimate ONE place past the smallest mark!

39. DENSITY - an important and useful physical property
Aluminum
Platinum
Mercury
13.6 g/cm3
21.5 g/cm3
2.7 g/cm3

40. Problem A piece of copper has a mass of 57. 54 g. It is 9
Problem A piece of copper has a mass of g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm3).

41. Strategy 1. Get dimensions in common units.
2. Calculate volume in cubic centimeters.
3. Calculate the density.

42. Note only 2 significant figures in the answer!
SOLUTION
1. Get dimensions in common units.
2. Calculate volume in cubic centimeters.
3. Calculate the density.
(9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm3
Note only 2 significant figures in the answer!

43. PROBLEM: Mercury (Hg) has a density of 13. 6 g/cm3
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg in grams? In pounds?

44. 1. Use density to calc. mass (g) from volume.
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg?
First, note that 1 cm3 = 1 mL
Strategy
1. Use density to calc. mass (g) from volume.
2. Convert mass (g) to mass (lb)
Need to know conversion factor
= 454 g / 1 lb

45. 2. Convert mass (g) to mass (lb)
PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg?
1. Convert volume to mass
2. Convert mass (g) to mass (lb)

46. Learning Check Osmium is a very dense metal. What is its
density in g/cm3 if g of the metal occupies
a volume of 2.22cm3?
1) g/cm3
2) 22.5 g/cm3
3) 111 g/cm3

47. Solution
2) Placing the mass and volume of the osmium metal into the density setup, we obtain
D = mass = g =
volume 2.22 cm3
= g/cm3 = g/cm3

48. Volume Displacement 25 mL
A solid displaces a matching volume of water when the solid is placed in water.
33 mL
25 mL

49. Learning Check
What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL?
1) 0.2 g/ cm ) 6 g/m ) g/cm3
33 mL
25 mL

50. Learning Check K V W V K W W V K
Which diagram represents the 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) ) ) K V W K V W W V K

51. Learning Check
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

52. Learning Check
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) L
3) L

53. Learning Check
A group of students collected 125 empty aluminum cans to take to the recycling center. If 21 cans make 1.0 pound of aluminum, how many liters of aluminum (D=2.70 g/cm3) are obtained from the cans?
1) 1.0 L 2) 2.0 L 3) 4.0 L