1. CH. 2 - MEASUREMENT

2. Qualitative (descriptive) Quantitative (numerical)
Observing and Collecting Data
Data may be
Qualitative (descriptive)
Flower is red
Quantitative (numerical)
100 flowers

3. Qualitative and Quantitative Data
Click below to watch the Visual Concept.
Visual Concept

4. Units of Measurement - Measurements represent quantities.
- A quantity is something that has magnitude, size, or amount.
- Measurement  quantity
the teaspoon is a unit of measurement
volume is a quantity
The choice of unit depends on the quantity being measured.

5. Quantity = number + unit
Number vs. Quantity
Quantity = number + unit
UNITS MATTER!!

6. SI Measurement Agreed upon single measurement system
Standard of measurement, constant value, easy to preserve, reproduce, and practical in size
Prefixes added to base units to represent quantities that are larger or smaller than the base

7. SI Base Units

8. SI Prefix Conversions Prefix Symbol Factor mega- M 106 kilo- k 103
BASE UNIT
---
100
deci- d
10-1
move left
move right
centi- c
10-2
milli- m
10-3
micro- 
10-6
nano- n
10-9
pico- p
10-12

9. M K H D B d c m u n p 0.2 32 45,000 0.0805 SI Prefix Conversions
1) 20 cm = ______________ m 2) L = ______________ mL 3) 45 m = ______________ nm 4) 805 dm = ______________ km
0.2 32
45,000
0.0805
M K H D B d c m u n p

10. M V D = 1 cm3 = 1 mL 1 m3 = 1 L Derived Units Density (kg/m3 or g/cm3)
Combination of units.
Volume amount of space occupied by an object
length  length  length
(m3 or cm3)
1 cm3 = 1 mL
1 m3 = 1 L
Density (kg/m3 or g/cm3)
mass per volume
D = M V

11. Derived SI Units

12. V = 825 cm3 M = DV D = 13.6 g/cm3 M = (13.6 g/cm3)(825cm3) M = ?
Density
An object has a volume of 825 cm3 and a density of 13.6 g/cm3. Find its mass.
GIVEN:
V = 825 cm3
D = 13.6 g/cm3
M = ?
WORK:
M = DV
M = (13.6 g/cm3)(825cm3)
M = 11,200 g
C. Johannesson

13. D = 0.87 g/mL V = M V = ? M = 25 g V = 25 g 0.87 g/mL V = 29 mL
Density
A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid?
GIVEN:
D = 0.87 g/mL
V = ?
M = 25 g
WORK:
V = M D
V = g
0.87 g/mL
C. Johannesson
V = 29 mL

15. The unit m3 is used to express ________
CH. 2 - MEASUREMENT
Review ??????
The unit m3 is used to express ________
One cubic centimeter is equivalent to ___
The relationship between the mass m of a material and its its volume V is __________

16. ACCURATE = CORRECT PRECISE = CONSISTENT
Accuracy & Precision
Accuracy - how close a measurement is to the accepted value
Precision - how close a series of measurements are to each other
ACCURATE = CORRECT
PRECISE = CONSISTENT

17. Accuracy and Precision
Click below to watch the Visual Concept.
Visual Concept

18. Indicate precision of a measurement.
Significant Figures
Indicate precision of a measurement.
Consists of all the digits known with certainty plus one final digit, which is somewhat uncertain or estimated
2.35 cm

19. Significant Figures Rules
Counting Sig Figs Count all numbers EXCEPT:
Leading zeros
Trailing zeros without a decimal point -- 2,500

20. Counting Sig Fig Examples
4 sig figs
3 sig figs
3. 5,280
3. 5,280
3 sig figs
2 sig figs

21. Calculating with Significant Figures
Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer.
(13.91g/cm3)(23.3cm3) = g
4 SF
3 SF
3 SF
324 g

22. Calculating with Significant Figures
Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer.
3.75 mL mL
7.85 mL
3.75 mL mL
7.85 mL
224 g
+ 130 g
354 g
224 g
+ 130 g
354 g
 7.9 mL
 350 g

23. Calculating with Significant Figures
Exact Numbers do not limit the # of sig figs in the answer.
Counting numbers: 12 students
Exact conversions: 1 m = 100 cm
“1” in any conversion: 1 in = 2.54 cm

24. Practice Problems (15.30 g) ÷ (6.4 mL) = 2.390625 g/mL  2.4 g/mL
4 SF
2 SF
= g/mL
 2.4 g/mL
2 SF
18.9 g g
 18.1 g
18.06 g

25. Scientific Notation WHY????
Don’t copy
WHY????
Chemistry often deals with very large and very small numbers.
There are 602,000,000,000,000,000,000,000 molecules of water in 18 mL
one electron has a mass of g
We need a shorter way of writing these numbers

26. 65,000 kg  6.5 × 104 kg Scientific Notation
Move decimal until there’s 1 digit to its left. Places moved = exponent.
Large # (>1)  positive exponent Small # (<1)  negative exponent
Only include sig figs.

27. Scientific Notation Practice Problems
7. 2,400,000 g kg 9. 7  10-5 km  104 mm
2.4  106 g
2.56  10-3 kg km
62,000 mm

28. Scientific Notation Calculations
(5.44 × 107 g) ÷ (8.1 × 104 mol) =
Type on your calculator:
EXP EE
EXP EE
ENTER
EXE
5.44 7
8.1 ÷ 4 =
= 670 g/mol
= 6.7 × 102 g/mol

29. Review ??????
Day 3
A chemical reaction was carried out three times. The mass of the product was 8.93 g for the first trial, 8.94 g for the second trial, and 8.92 g for the third trial. Under the conditions of the experiment, the reaction is known to yield 8.60 g of product. The three mass values measured are?

30. Conversion Factors
A conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other.
example: How quarters and dollars are related

31. Conversion Factors, continued
Dimensional analysis is a mathematical technique that allows you to use units to solve problems involving measurements.
quantity sought = quantity given × conversion factor
example: the number of quarters in 12 dollars
number of quarters = 12 dollars × conversion factor

32. Click below to watch the Visual Concept.

33. Using Scientific Measurements
Direct Proportions
Two quantities are directly proportional to each other if dividing one by the other gives a constant value.
variables do the same thing

34. Using Scientific Measurements
Inverse Proportions
Two quantities are inversely proportional to each other if their product is constant.
variables do the opposite

35. Percent Error your value accepted value
Indicates accuracy of a measurement
your value
accepted value

36. % error = 2.9 % Percent Error
A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.
% error = 2.9 %