General Chemistry Fall ‘09. People often confuse Controls & Variables in experiments A...

General Chemistry

Fall ‘09

People often confuse Controls & Variables in experiments

A control is… A trial that duplicates all conditions except the

variable being investigated A variable is…

Either dependent (responding)- this is observed during the experiment

Or independent (manipulated)- what you (I) change during an experiment

People often confuse Observations &

Hypotheses An observation…

Is information collected with the senses

A hypothesis… A proposed explanation

for an observation.

Ivan Pavlov observed dogs salivating and

hypothesized that a sound would cause

dogs to salivate.

Identify the following as an observation or a hypothesis 1. Wearing tennis shoes will make one run faster.

2. The tennis shoes are black and red.

3. The Bunsen Burner flame is 1400°C and is blue.

4. People who take good notes will do better on tests.

Hypothesis

Observation

Observation

Hypothesis

Scientists make observations all the time. There’s two types:

Qualitative Quantitative

To remember the difference, look at their root

Qualities of the reaction, object, etc. Examples

The copper (II) sulfate is blue The nail is rusty Gas was given off

http://upload.wikimedia.org/wikipedia/commons/d/d8/Copper_sulfate.jpg

http://www.learner.org/channel/courses/essential/physicalsci/images/s4.rusty_nail.jpg

Quantity= numbers Mass, a number of paper clips, volume

measurements, molar measurements. Math is usually involved

Theory A well-tested explanation for a broad set of

observations Can help predict the behavior of matter and form

mental images Can be modified if new observations are made

Scientific Law A concise statement that summarizes the results of

many observations and experiments. Do not describe relationships, that requires a theory Ex) Charles’ Law

Scientific notation A number is written as the product of two numbers

A coefficient 10 raised to a power

Example: 602,000,000,000,000,000,000,000 Written as 6.02x1023

Coefficient is equal to or greater than 1 and smaller than 10

Try these:

1. 200,000,000,000 = ___________________

2. 0.00073 = ____________________

3. 1430 = __________________

If exponent is negative, which way does decimal go? If exponent is positive, which way does decimal go?

“Correctness” and “reproducibility” Accuracy

A measure of how close a measurement comes to the actual or true value of whatever is measured

Precision A measure of how close a series of measurements

are to one another

Measurements may be accurate or inaccurate Accepted value- correct value, based on

reliable resources Experimental value- value measured in the lab The difference between the two is called error

The absolute value of the error divided by the accepted value, multiplied by 100%

Example: boiling point was measured to be 99.1oC, but we know it’s 100oC

%error = 99.1oC – 100oC x100% 100oC

%error = 0.9%

Metric system is much easier than the English system…the conversion is always a factor of 10.

SI Base Units

Quantity SI Base Unit Symbol

Length meter m

Mass kilogram kg

Temperature kelvin K

Time second s

Amount mole mol

Length is a 1-dimensional measure of distance. Metric system base unit is the meter,

abbreviated m

Commonly Used Metric Prefixes

Prefix Meaning Factor

Mega (M) 1 million x larger 106

Kilo (k) 1000x larger 103

Deci (d) 10x smaller 10-1

Centi (c) 100x smaller 10-2

Milli (m) 1000x smaller 10-3

Micro 1 million x smaller 10-6

Nano (n) 1000 x smaller 10-9

Pico (p) 1 trillion x smaller 10-12

Volume is a measure of the amount of space a substance takes up. Metric system base unit is the liter,

abbreviated L.

Mass is a measure of the amount of matter in a substance. Metric system base unit is the

kilogram, abbreviated kg

• Response of mass to the pull of gravity

• Weight changes when on different planets

• NOT THE SAME AS MASS!

A measure of how hot or cold an object is.

Heat moves from hot to cold Celsius scale

Freezing point = Boiling point =

Kelvin scale Freezing point = 273 kelvins (K) Boiling point = 373 K Absolute zero = 0K (zero kinetic

energy)

Kilo hecto deka (m, g, L) deci centi milli k h dk or D d c m

How do you remember the order of the prefixes?

kilo

1000 hecto

100 deka

10 Base

Unit deci

1/10 centi

1/100 milli

1/1000

To convert to a larger unit, move the decimal point to the left or divide:

To convert to a smaller unit, move the decimal point to the right or multiply:

kilo

1000 hecto

100 deka

10 Base

Unit deci

1/10 centi

1/100 milli

1/1000

Convert 6 cm = _____ mm

We are converting to:

a) larger unit

b) smaller unit

Convert 6 cm = 60 mm

kilo

1000 hecto

100 deka

10 Base

Unit deci

1/10 centi

1/100 milli

1/1000

Convert 40 mm = _____ cm

We are converting to:

a) larger unit

b) smaller unit

Convert 40 mm = 4 cm

kilo

1000 hecto

100 deka

10 Base

Unit deci

1/10 centi

1/100 milli

1/1000

Convert 90 cm = _____ m

We are converting to:

a) larger unit

b) smaller unit

Convert 90 cm = 0.9 m

kilo

1000 hecto

100 deka

10 Base

Unit deci

1/10 centi

1/100 milli

1/1000

Convert 200 mm = _____ m

We are converting to:

a) larger unit

b) smaller unit

Convert 200 mm = 0.2 m

Make the following metric conversions 1. 875 cm = _________ m

2. 1.24 km = _________ m

3. 90,344 m = _________ km

4. 0.95 km = _________cm

8.75

1,240

875 / 100

1.24 x 1000

There is always an error in a measurement

The human eye can read one decimal place beyond the accuracy of the instrument

The measurement should be read

as 8.0 +/-0.1cm.

65

60

55

10

9

8

150

100

50

Container #1 Container #2 Container #39.02 mL 82 mL 62.0 mL

Read the volumes of the liquids below