1. Chapter 2

2. Quantitative measurements
give results in a definite form, usually a number
Example
Thermometer

3. Qualitative measurements
gives results in a descriptive form
non-numeric value
Example
Color of a reaction

4. Accuracy
How close a measurement comes to the true value
Precision
Reproducibility of the measurement

5. Significant Figures
include all digits that can be known accurately plus a last digit that is estimated

6. Rules for Significant Figures
Every nonzero digit in a recorded measurement is significant
Examples
65.2
0.268
126
(All have 3 Sig. Figs.)

7. 2. Zeros between nonzero digits are significant
Example
2004
60.39
8.602
(All have 4 Sig. Figs.)

8. 3. Zeros in front of all nonzero digits are NOT significant
3. Zeros in front of all nonzero digits are NOT significant. They act as place-holders.
Examples
0.0062
0.58
(2 Sig. Figs.)

9. 4. Zeros at the end of a number and to the right of a decimal point are significant
Examples
61.00
1.030
8.000
(4 Sig. Figs.)

10. Zeros at the end of a measurement and to the left of the decimal can be confusing.
If they are place-holders to show the magnitude of a number, they are not significant

11. Examples
ambiguous
If the zeros were measured- significant
700.

12. To avoid confusion use scientific notation
3.00 x 10 2

13. How Many Sig. Figs.?
123  3
98,000  2
40,506  5  4
0.123  3
0.078  2
x 10 4  5

14. Sig. Figs in calculations
If digit following last sig fig is <5, all digits are dropped
If digit following last sig fig is >5, digit in last sig fig place is increased by one

15. Round These…….
4 sig figs
314.7
2 sig figs
0.0018
64.32 x 10 -1
1 sig fig
60 x or 6

16. Addition and Subtraction
The answer cannot contain any more digits to the right of the decimal point than are contained in the measurement with the least number of digits to the right of the decimal point

17. Sample Problem
12.52 +
349.0 +
8.24
369.8 or x 10 2

18. Multiplication and Division
Answer must contain no more sig figs than the measurement with the least number of sig figs.
*Decimal point has nothing to do with determining this!

19. Example Problems
755 x .034 = 26
3 sig. figs.
2 sig. figs
2 sig. figs
 8.4 =
0.29

20. Metric System
SI system (International System of Units)- Developed in 1790 in France

21. Quantity SI Unit Non-SI Length m Volume m3 Liters Mass kg grams
Density g/cm³, g/ml
Temperature K oC
Time s
Pressure pa (pascal) atmospheres, mm Hg
Energy J (joules) calories

22. Units of Measurement – Meter (m)
Prefix Symbol Magnitude
kilo K x
hecto h 100x
deca da 10x
unit m, L, g x
deci d .1x
centi c .01x
milli m x
micro u 1 x x
nano n 1 x x
pico p 1 x x

23. Units of Volume – Liter (L)
Volume of a cube-10 cm x 10 cm x 10 cm= 1000 cm 3
1 L = 1 dm 3 = 1000 cm 3
1 cm 3 = 1 mL

24. Units of Mass – (g) Mass- quantity of matter Weight- a force
Unit of mass – gram (g) =
mass of 1 cm 3 of H2O at 4 ºC

25. Density- ratio of mass of an object to volume
D= M = g/mL or g/cm 3 V

26. Specific Gravity
Specific Gravity- comparison of the density of a substance to the density of a reference substance

27. Specific Gravity Cont’d
Sp. Gravity = density of substance g/cm 3
density of H2O g/cm 3
Sp. Gravity of a liquid is measured with a hydrometer

28. Temperature- Degree of hotness or coldness of an object
Determined direction of heat transfer
Heat transfer- occurs when two objects at different temperatures contact each other
Heat goes from high temperature to low temp

29. Temperature Scales 32ºF - FP of H2O 212ºF - BP of H2O
Fahrenheit
32ºF - FP of H2O
212ºF - BP of H2O
Celsius (centigrade)
0ºC - FP of H2O
100ºC - BP of H2O
Kelvin
273 K - FP of H2O K = oC + 273
373 K - BP of H2O

30. Heat Heat- measured in joule (J) or calories (cal)
One calorie is the quantity of heat that raises the temperature of 1 g of H2O 1ºC
1 cal = 4.18 J
Calorie in nutritional terms means kilocalorie

31. Heat Cont’d
Heat Capacity- quantity of heat required to change an objects temperature by exactly 1ºC
Depends on mass and type of substance

32. Specific Heat
The quantity of heat required to raise 1g of a substance 1ºC
Sp. Heat = heat = q
mass x T (m) (T)
Units of Specific Heat:
J/g°C or cal/g°C

33. Problem Solving in Chemistry
Chapter 2B
Problem Solving in Chemistry

34. Three easy steps to problem solving. . .

35. Step 1 : Analyze Identify a known
Determine where you are starting from.
What information do you already have to work with?

36. Step 1 cont’d… Identify an unknown Where are you going?
What are you looking for?
Plan a solution
How are you going to get there?

37. Step 2: Calculate
May involve substituting known quantities and doing the arithmetic needed to solve for unknown.
You may also need to convert.

38. Step 3: Evaluate Go over your answers Check your work
Does the answer make sense?
Did you use correct units?
Check your work
Make sure you copied down the given information correctly.

39. Sample Problem
What is the mass, in grams, of a piece of lead that has a volume of cm³?

40. Step 1 : Analyze List Knowns and Unknowns Knowns :
Volume of lead: cm³
Density of lead = 11.4 g/cm³ (according to table 3.7)
Density = mass
volume
Unknowns: mass = ?g

41. Step 2: Calculate Density = mass -or- Mass = volume x density volume
Mass = cm ³ x 11.4 g/cm ³
= g
Mass = 226 g

42. Step 3: Evaluate Has the unknown been found?
Yes, problem asks for mass
Do you have the correct units?
Yes, units canceled correctly to yield grams (g)
Is the number of sig figs correct?
Yes, answer has 3 sig figs
Mass = 226 g

43. What is the volume, in cubic centimeters of a sample of cough syrup that has a mass of 50.0g? The density of cough syrup is 0.950g/cm³.

44. density Volume = 50.0g = 52.6316 cm³ 0.950g/cm³ Volume = 52.6 cm³
Volume = mass
density
Volume = 50.0g = cm³
0.950g/cm³
Volume = 52.6 cm³

45. Your school club has sold 600 tickets to a chili-supper fundraising event, and you have volunteered to make chili. You have a chili recipe that serves 10. The recipe calls for two teaspoons of chili powder. How much chili powder do you need for 600 servings?

46. 600 servings x 2 tsp chili powder = 10 servings
Servings Needed = 600
10 servings = 2 tsp chili powder
Amount of chili powder = ? tsp
600 servings x tsp chili powder =
10 servings
1200 tsp chili powder = 120 tsp chili powder 10

47. How many cups are in 120 teaspoons of chili powder?

48. 120 tsp x 1 tbs x 1 cup =
3 tsp tbs
120 cups = cups 48

49. Express 750 dg in grams

50. Mass = 750 dg
1 g = 10 dg
Mass = ?g
750 dg x 1g = 75 g
10 dg

51. What is km in cm?

52. 0.073 km x m x 100 cm =
1 km m
7300 cm = cm 1

53. How many seconds are in one day?

54. 1 day x h x min x 60 s =
1 day h min
86400 s = x 104 s 1