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Unit 1: Scientific Processes and Measurement

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Unit 1: Scientific Processes and Measurement

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Unit 1: Scientific Processes and Measurement

Science: man made pursuit to understand natural phenomena

Chemistry: study of matter

Hazard Symbols

blue – healthred – flammability

yellow – reactivitywhite – special codes

Scale: 0 to 4

0 = no danger

4 = extreme danger!

- gives important information about chemicals
first aid, fire-fighting, properties, disposal, handling/storage, chemical formula…

- General set of guidelines used in an experiment

- Testable statement based on observations; can be disproven, but not proven

- A)Bacterial growth increases exponentially as temperature increases.
- B) A fish’s ability to taste food is affected by the clarity of aquarium water.
- C) Tadpoles’ fear of carnivorous insect larvae increases as the tadpoles age.
- D) The number of times a dog wags its tail indicates how content the dog is.

- States phenomena but does not address “why?”
- Examples: Newton’s Laws of Motion, Law of Conservation of Mass

- Broad generalization that explains a body of facts
- Summarizes hypotheses that have been supported through repeated testing

Non-numerical descriptions in an experiment

Example: Color is blue…

- Observations that are numerical
- Example: the mass is 9.0 grams

Independent Variable: variable that is being changed or manipulated by YOU

Dependent Variable: variable that responds to your change ---- what you see

Controlled Variables: variables that you keep the same

Control or Control Set-up: used for comparison; allows you to measure effects of manipulated variable

Directly proportional: when one variable goes up, the other also goes up

Indirectly proportional: when one variable goes up, the other goes down

The diagram shows different setups of an experiment to determine how sharks find their prey. Which experimental setup is the control?

A) Q

B) R

C) S

D) T

- “DRY MIX” - way to remember definitions and graphing
- DRY – dependent, responding, y-axis
- MIX – manipulated, independent, x-axis

Measurement - quantitative observation

consisting of 2 parts

Part 1 - number

Part 2 - scale (unit)

Examples:

- 20grams
- 6.63 x 10-34Joule seconds

- Volume
- Temperature
- Mass

Always read volume from the bottom of the meniscus. The meniscus is the curved surface of a liquid in a narrow cylindrical container.

Parallaxerrors arise when a meniscus or needle is viewed from an angle rather than from straight-on at eye level.

Correct: Viewing the meniscusat eye level

Incorrect: viewing the meniscusfrom an angle

The glass cylinder has etched marks to indicate volumes, a pouring lip, and quite often, a plastic bumper to prevent breakage.

- Determine the volume contained in a graduated cylinder by reading the bottom of the meniscus at eye level.
- Read the volume using all certain digits and one uncertaindigit.

- Certain digits are determined from the calibration marks on the cylinder.

- The uncertain digit (the last digit of the reading) is estimated.

There are two unlabeled graduations below the meniscus, and each graduation represents 1 mL, so the certain digits of the reading are…

52 mL.

The meniscus is about eight tenths of the way to the next graduation, so the final digit in the reading is .

0.8 mL

The volume in the graduated cylinder is

52.8 mL.

What is the volume of liquid in the graduate?

6

6

_ . _ _ mL

2

What is the volume of liquid in the graduate?

5

2

7

_ _ . _ mL

Examine the meniscus below and determine the volume of liquid contained in the graduated cylinder.

The cylinder contains:

7

6

0

_ _ . _ mL

- Determine the temperature by reading the scale on the thermometer at eye level.
- Read the temperature by using all certain digits and one uncertain digit.

- Certain digits are determined from the calibration marks on the thermometer.
- The uncertain digit (the last digit of the reading) is estimated.
- On most thermometers encountered in a general chemistry lab, the tenths place is the uncertain digit.

If the thermometer bulb touches the flask, the temperature of the glass will be measured instead of the temperature of the solution. Readings may be incorrect, particularly if the flask is on a hotplate or in an ice bath.

Determine the readings as shown below on Celsius thermometers:

8

7

4

3

5

0

_ _ . _ C

_ _ . _ C

Our balances have 4 beams – the uncertain digit is the thousandths place ( _ _ _ . _ _ X)

In order to protect the balances and ensure accurate results, a number of rules should be followed:

- Always check that the balance is level and zeroed before using it.
- Never weigh directly on the balance pan. Always use a piece of weighing paper to protect it.
- Do not weigh hot or cold objects.
- Clean up any spills around the balance immediately.

- Determine the mass by reading the riders on the beams at eye level.
- Read the mass by using all certain digits and one uncertain digit.

- The uncertain digit (the last digit of the reading) is estimated.
- On our balances, the hundredths place is uncertain.

1. Place object on pan

2. Move riders along beam, starting with the largest, until the pointer is at the zero mark

1

1

4

? ? ?

_ _ _ . _ _ _

1

1

4

4

9

7

_ _ _ . _ _ _

- A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.

- Measurements are performed with instruments
- No instrument can read to an infinite number of decimal places

Which of these balances has the greatest uncertainty in measurement?

Accuracy refers to the agreement of a particular value with the truevalue.

Precisionrefers to the degree of agreement among several measurements made in the same manner.

Precise but not accurate

Precise AND accurate

Neither accurate nor precise

- Nonzero integersalways count as significant figures.
- 3456has
- 4sig figs.

- Zeros
- Leading zeros do not count as
significant figures.

- 0.0486 has
- 3 sig figs.

- Zeros
Captive zerosalways count as

significant figures.

- 16.07has
- 4 sig figs.

- Zeros
- Trailing zerosare significant only if the number contains a decimal point.
- 9.300 has
- 4 sig figs.

- Exact numbershave an infinite number of significant figures.
- 1 inch = 2.54cm, exactly

How many significant figures in each of the following?

1.0070 m

5 sig figs

17.10 kg

4 sig figs

100,890 L

5 sig figs

3.29 x 103 s

3 sig figs

0.0054 cm

2 sig figs

3,200,000

2 sig figs

- Multiplication and Division:# sig figs in the result equals the number in the least precise measurement used in the calculation.
- 6.38 x 2.0 =
- 12.76 13 (2 sig figs)

Calculation

Calculator says:

Answer

22.68 m2

3.24 m x 7.0 m

23 m2

100.0 g ÷ 23.7 cm3

4.22 g/cm3

4.219409283 g/cm3

0.02 cm x 2.371 cm

0.05cm2

0.04742 cm2

710 m ÷ 3.0 s

236.6666667 m/s

240 m/s

5870 lb·ft

1818.2 lb x 3.23 ft

5872.786 lb·ft

2.9561 g/mL

2.96 g/mL

1.030 g ÷ 2.87 mL

- Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement.
- 6.8 + 11.934 =
- 18.734 18.7 (3 sig figs)

Calculation

Calculator says:

Answer

10.24 m

3.24 m + 7.0 m

10.2 m

100.0 g - 23.73 g

76.3 g

76.27 g

0.02 cm + 2.371 cm

2.39 cm

2.391 cm

713.1 L - 3.872 L

709.228 L

709.2 L

1821.6 lb

1818.2 lb + 3.37 lb

1821.57 lb

0.160 mL

0.16 mL

2.030 mL - 1.870 mL

Scientific Notation

In science, we deal with some very LARGE numbers:

1 mole = 602000000000000000000000

In science, we deal with some very SMALL numbers:

Mass of an electron =

0.000000000000000000000000000000091 kg

Imagine the difficulty of calculating the mass of 1 mole of electrons!

0.000000000000000000000000000000091 kg

x 602000000000000000000000

???????????????????????????????????

Scientific Notation:

A method of representing very large or very small numbers in the form:

M x 10n

- M is a number between 1 and 10
- n is an integer

.

2 500 000 000

9

7

6

5

4

3

2

1

8

Step #1: Insert an understood decimal point

Step #2: Decide where the decimal must end

up so that one number is to its left

Step #3: Count how many places you bounce

the decimal point

Step #4: Re-write in the form M x 10n

2.5 x 109

The exponent is the number of places we moved the decimal.

0.0000579

1

2

3

4

5

Step #2: Decide where the decimal must end

up so that one number is to its left

Step #3: Count how many places you bounce

the decimal point

Step #4: Re-write in the form M x 10n

5.79 x 10-5

The exponent is negative because the number we started with was less than 1.

Review:

Scientific notation expresses a number in the form:

M x 10n

n is an integer

1 M 10

2 x 106 is entered as 2 2nd EE 6

EE means x 10

If you see E on your calculator screen, it also means x 10

2 x 1014 / 3 x 10-3 = ?

2 x 10-34 x 3 x 1023

4.5 x 1023 / 5.26 x 10-14

Kilo1031000KING

Hecta 102100HENRY

Deca10110DIED

Unit 1001UNEXPECTEDLY

Deci10-10.1DRINKING

Centi10-20.01CHOCOLATE

Milli10-30.001MILK

1 L = 1000 mL1 Hm = ______ m

1 m = ____ cm1 Dm = _____ m

1 kg = 1000 g___ dm = 1 m

Tera10121,000,000,000,000THE

Giga1091,000,000,000GREAT

Mega1061,000,000MIGHTY

Kilo1031000KING

Hecta 102100HENRY

Deca10110DIED

Unit 1001UNEXPECTEDLY

Deci10-10.1DRINKING

Centi10-20.01CHOCOLATE

Milli10-30.001MILK

Micro10-60.000001MAYBE

Nano10-90.000000001NOT

Pico10-120.000000000001PASTUERIZED?

1 L = 1000 mL1 m = ______ nm

1 m = ____ cm1 Dm = _____ m

1 kg = 1000 g___ dm = 1 m

1 Mm = _____ m1 Gb = _____ byte