Chemistry and chemicals

In every measurement, a number must be followed by a unit to have any meaning... The Metric System SIThe metric system and SI international system are  related decimal systems based on

Chemistry in Our Lives

Chemistry and Chemicals

Chemistry is the study of substances in terms of

Composition What a material it made of

Structure How the elementary particles are put together

Properties The characteristics of the material

Reactions How it behave with other substances

What is chemistry?

Chemical reactions happen when

• a car is started

• tarnish is removed from silver

• fertilizer is added to help plants

grow

• food is digested

• electricity is produced from

burning natural gas

Everything in our lives from materials

to life involve chemistry

• glass (SiO2)n

• metal alloys

• chemically treated water

• plastics and polymers

• baking soda, NaHCO3

• foods

• fertilizers and pesticides

• living beings

Chemicals in Toothpaste

The Scientific Method

The scientific method is the

process used to explain

Everyday Scientific Thinking

• Observation: The sound from a CD in a CD

player skips

• Hypothesis 1: The CD or player is faulty

• Experiment 1: When the CD is replaced with another

one, the sound from the second CD is OK

• Hypothesis 2: The original CD has a defect

• Experiment 2: When the original CD is played in another

player, the sound still skips

• Theory: The experimental results suggest that

Units of Measurement

In chemistry:

quantities are measured

experiments are performed

results are calculated

use numbers to report measurements, results are compared to standards.

In a measurement of the thickness

of the skin fold at the waist,

calipers are used.

A measuring tool is used to

compare some dimension

of an object to a standard.

In every measurement, a number must be followed by a unit

to have any meaning.

Observe the following examples of measurements:

Number and Unit

35 m (meter) 0.25 L (liter)

225 lb (pound) 3.4 h (hour)

The Metric System (SI)

The metric system and SI (international

system) are

 related decimal systems based on 10

 used in most of the world

 used everywhere by scientists

Length

 is measured using a meter stick

 uses the unit meter

(m) in both the metric and SI systems

The unit of an inch

Volume

 is the space occupied

 by a substance

 the unit of volume is the

system

1 L = 1.06 qt

The mass of an object

 is a measure of the quantity of material it contains

 the unit gram (g) or kilogram (1000 g) is used

What is the difference between mass and weight?

Weight is the result of the action of gravity on mass Your weight

on the moon would be a lot less even though your mass would

remain the same

Despite this important difference, we will use these two terms interchangeably

The temperature

 indicates how hot or cold a

substance is

 the Celsius (°C) scale is used

in the metric system

 the Kelvin (K) scale is also

Time measurement

 the unit second (s) is

used in the metric

system.

 Time is based on an

atomic clock that uses a frequency emitted by cesium atoms

Scientific notation

 is used to write very large or very small numbers

 the width of a human hair (0.000 008 m) is written

8 x 10-6 m

 a large number such as 4 500 000 s is written

4.5 x 106 s

10 -3 /10 5 = 10 -8

What is the length of this piece of wood?

What is the first digit? Any uncertainty in the digit? 4

What is the second digit? Any uncertainty in this digit? 4.5

What is the third digit? Any uncertainty in this digit? 4.56

Definition of a significant figure:

Significant digits include all digits with no uncertainty plus one estimation

4 2 5 2 2

A Exact numbers are obtained by

3 definition

B Measured numbers are obtained by

1 using some measuring tool

Classify each of the following as exact (E) or

measured (M) numbers Explain your answer

A Gold melts at 1064 °C

B 1 yard = 3 feet

C The diameter of a red blood cell is 6 x 10-4 cm

D There are 6 hats on the shelf

Significant Figures

In calculations:

 Answers must have the same

number of significant figures

as the measured numbers

 Calculator answers must often

be rounded off.

 Rounding rules are used to

obtain the correct number of

significant figures

Rounding Off

 When the first digit dropped is 4 or less, the retained

numbers remain the same

To round 45.832 to 3 significant figures

drop the digits 32 = 45.8

 When the first digit dropped is 5 or greater,

the last retained digit is increased by 1

To round 2.4884 to 2 significant figures

Multiplication and Division

When multiplying or dividing use

 the same number of significant figures (SF) as the

measurement with the fewest significant figures

Example:

110.5 x 0.048 = 5.304 = 5.3

4SFs 2SFs calculator 2SFs

Addition and Subtraction

When adding or subtracting, use

 the same number of decimal places as the

measurement with the fewest decimal places

25.2 one decimal place

+ 1.34 two decimal places

26.54 calculated answer

For each calculation, round the answer to give the correct number of decimal places.

A 235.05 + 19.6 + 2 =

1) 257 2) 256.7 3) 256.65

B 58.925 – 18.2 =

1) 40.725 2) 40.73 3) 40.7

1m/100cm = 1; 1m/1000mm = 1

An equality

 states the same measurement in two different units

 can be written using the relationships between two

metric units

Example: 1 meter is the same as 100 cm and 1000 mm.

1 m = 1000 mm

volume has the dimensions of length cubed

 Several equalities can be

written for mass

1 kg = 1000 g

1 g = 1000 mg

1 mg = 0.001 g

Some Common Equalities

• An injured person loses 0.30 pints of blood How many milliliters of blood would that be?0.30pt*1qt/2pt = 0.15qt; 0.15qt*946mL/qt = 141.9 mL; 140 mL

• If a person weighs 200 pounds, how many kiograms does the person weight?

• 200 lb*1 kg/2.2 lb = 90.9 kg

• 200 lb*2.2 lb/1 kg = 440 lb2/kg

If the thickness of the skin fold at the

waist indicates an 11% body fat, how

much fat is in a person with a mass

Density

compares the mass of an object to its volume

is the mass of a substance divided by its volume

Density expression:

D = mass = g or g = g/cm3

volume mL cm3

Osmium is a very dense metal What is its density in g/cm 3 if 50.0 g of osmium has a volume of 2.22 cm 3 ?

1) 2.25 g/cm 3

2) 22.5 g/cm 3

3) 111 g/cm 3

• The density of the zinc object

can be calculated from its

mass and volume

d = 68.6g/(45.0-35.5)mL; 68.6g/9.5 mL

d = 7.2 g/mL