Homework

Read Pgs. 11-13Chapter 1 Problems 20, 24, 26,30Worksheet Scientific Measurement (2A

Extra Practice Problems)

Significant figures

Addition and SubtractionThe answer must have the

same number of decimal places as the factor with the least number of decimal places.

Significant Figures

Example of Addition:

1250

+ 23.98

1273.98 (this is what a calculator will show)

1274 (this is the answer corrected for significant figures, rounded to the 1’s place)

Significant figures

Multiplication and divisionThe answer must have the

same number of significant figures as the factor with the least number of significant figures.

Significant figures

Example of Division:

15.375 / 5.0 = 3.075(this is what a calculator will show)

Since the denominator only has 2 significant figures the answer is rounded to 3.1

Significant Figures

8.654 m x 0.34 m =2.10 cm x 0.50 cm =

10.4815 ml ÷ 8.4 ml = 0.365 m ÷ 0.050 m =

textbook HW20a. 3 26a. 132.5 g

b. 4 b. 298.69 cm

c. 4 c. 13 lb

d. 1 d. 350 oz

e. 5 30. only c is exact

24a. 0.5

b. 401.4

c. 0.2684

d. 7.8

Scientific Measurement1 a. 3 2 a. 133 g e. 50.8 dm

b. 4 b. 109 mL f. 2.86x103 cal

c. 7 c. 13 cm

d. 2 d. 14 g/mL

e. 3 f. 63 a. 1.0 e. 740. 4a. 145g e.

1.30x102dm

b. 40.1 f. 80 b. 64mL f. 16 cm

c. 6.2x10-5 c. 91.7 cm2 g. 6000cal

d. 1.5 d. 4.3g/cm3

Unit 1

Read pages 8-9Unit 1 Sci. Notation and % ErrorChapter 1 Problems 20, 24, 26,30Quiz: Oct 18/19 (Thursday / Friday)

Numbers and Measurement

Chemistry requires us to make accurate measurements that are often very small or very large.

To more easily handle these very large and small numbers, we use scientific notation.

Scientific Notation

Measurements are written as the product of two numbersA coefficient – number between 1 and 1010 raised to a power – the exponent

indicates the number of times the coefficient must be multiplied or divided by 10.

Scientific Notation

Write the following in scientific notation:6,954,000175.983

Write the following in standard numerical form:6.75 x 10-3

1.865 x 102

Calculations in Scientific Notation

MultiplicationMultiply coefficientsAdd exponents

Perform the following calculations:7.2 x 102 · 5.02 x 10-3

1.0 x 102 · 2.6 x 108

Calculations in Scientific Notation

DivisionDivide coefficientsSubtract the exponent of the denominator

from the exponent of the numerator.Perform the following calculations:

8.4 x 103 / 2.1 x 10-2

7.25 x 104 / 5.0 x 102

Calculations in Scientific Notation

Addition and subtractionMake the exponent of both numbers the

sameAlign decimal points, and add coefficientsThe exponent of the result will be the same

as for the measurements

Calculations in Scientific Notation

Perform the following calculations:1. 6.3 x 104 + 2.1 x 10-3

2. 7.563 x 102 - 1.77789 x 10-3

Calculations in Scientific Notation

1. 1.5 x 106 + 2.7 x 103

2. 6.38 x 10-3 – 3.8 x 10-4

International System of Units

Units of Measurement

Quantity SI base unit or derived unit Symbol

Length meter m

Volume cubic meter m3

Mass kilogram kg

Density grams per cubic centimeter g/cm3

Temperature Kelvin K

Time second s

Pressure Pascal Pa

Energy joule J

Amount of Substance mole mol

Luminous Intensity candela cd

Electric Current ampere a

SI Units

103 for kilo- k 106 for mega- M 109 for giga- G 10-1 for deci- d 10-2 for centi- c 10-3 for milli- m 10-6 for micro- μ 10-9 for nano- n 10-12 for pico- p

Accuracy: Evaluations of Measurements

Accepted value: True or correct value based on reliable source

Experimental value: measured by you during the experiment

Error

Difference between the accepted value and the experimental value

Take the absolute value

% Error

% Error = Error / accepted value * 100

% Error = Actual – Experimental x 100

Actual

What is the % error?

A student measures a volume as 25.0mL, whereas the correct volume is 23.2mL.

Density

Which is heavier – a pound of popcorn or a pound of cheese?

They would have the same mass!!

However, if you had equal VOLUMES of popcorn and cheese, the cheese would have more mass.

Density

A cube of gold-colored metal with a volume of 64 cm3 has a mass of 980. grams. The density of pure gold is 19.3 g/cm3. Is the metal pure gold?

Unit 1

HW: Read pages 9-10Unit 1: Density and TemperatureMore Conversion Problems

Temperature

The temperature of an object determines the flow of heat transfer.

Celsius scale uses the freezing point of water as 0 and the boiling point of water as 100.

Kelvin scale uses 273 for the freezing point of water, and 373 as the boiling point.

(Gabriel) Fahrenheit Scale

German physicistDeveloped scale in 1714Hg was used in thermometerFreeze pt. water = 32˚FBoiling pt. water = 212˚F0˚F = freeze pt. of water, salt and

dry ice (CO2)

Why use Hg in a thermometer?

For every degree the mercury’s temp. increases, the difference in which the Hg expands is NOTICABLE and CONSTANT.

Alcohol thermometer used in Alaska because Hg will freeze!

(Anders) Celsius Scale

Developed in 1742Swedish AstronomerFreezing pt. of water = 0˚CBoiling pt. of water = 100˚CUses Hg in thermometer

325

9 CF

(Lord William) Kelvin ScaleDeveloped in 1848Based on absolute zero = zero heat energy

= all motion stops0 Kelvin = -273.15˚CNo degree on scale (Kelvin units)Kelvin is a theoretical scale because it does

not compare the temp. to FP or BP of water.Based on lowest temperature possible – No

negative numbers on scale

Compare the 3 temperature scales