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2.1 Importance of Measurement

2.2 Accuracy and Precision

2.3 Scientific Notation

2.4 Significant Figures in Measurement

2.5 Sig. Figs. In Calculations

2.6 S.I., International System

2.7-2.9 Length, volume, and Mass2.10-2.12 Density, specific gravity and Temperature

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The Importance of Measurement

Qualitative Measurement

 ±  Give results in descriptive

nonnumeric form.

Examples:

 ±  Observing a color change

 ±  Production of bubbles

 ±  texture

Quantitative Measurement

 ±  Give results in a definite

form, usually as numbers.

Examples:

 ±  Mass increased by .098 g

 ±  The volume doubled

You must be able to make measurements in order to perform

Experiments and learn concepts in chemistry.

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Accuracy vs. Precision:

What is the difference?

Precision is reproducibility of measurement.

Accuracy is how close the measurement is to the

accepted value.

When I placed the same object on a balance 5 times, the results were as

Follows: 3.45 g, 3.44 g, 3.46 g, 3.44 g, 3.45 g

What do all the measurements have in common?

How do they differ?

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When I placed the same object on a balance 5 times, the results were as

Follows: 3.44 g, 3.45 g, 3.46 g, 3.44 g, 3.45 g

Is this balance accurate if the accepted value is 4.45?

Can a balance be precise but not accurate?

Explain.

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When using very large or very small numbers it s not

Convenient to write them out.

Ex. The mass of a proton is:

0.000 000 000 000 000 000 000 001 67 g

In order to shorten this up we are going to get rid of the place

Holders.

We will multiply a coefficient and a power of 10.

The coefficient must be 1<C<10

1.67 X 10-24g

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 All digits know for certain Plus one estimate are

significant digits

What is the volume?

Volume in ml

What is known for certain?

What is the estimate?

Rule#1:

All nonzero digits are

Significant.

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R ule#2: Zeros to the right of a nonzero digit are not

significant!

What is the volume?

Has there been a

measurement made in the

ones place?

It is just a place holder 

If a zero helps to show the

magnitude of a

measurement it is notsignificant.

To avoid confusion, use

scientific notation to get rid

of placeholders.

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R ule3: Z eros in between non zero digits are

significant .

What is the volume

What units places have

 been measured. How many sig. Figs?

If a units place has

 been measured and

there is less than one

in that place, it is

significant.

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R ule # 4 Z eros to the right of the decimal point and to

the right of non zero digits are significant .

What is the volume?

Is the meniscus right

on the line?

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R ule#5: Z eros to the right of the decimal point and to the left of 

non zero digits are not significant .

Has a measurement been made

in the tenths place?

How about the hundredth¶s

 place? The balance does not start

working until the thousandths

 place.

The 3 zeros to the left of the

non zero digits are helping us tounderstand the magnitude of the

measurement.

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There are no significant figures if the value is

counted or is defined.

Examples: There are 100 cm in one meter.

This is a definition.

He scored 5 goals.

Exact value

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Addition and Subtraction:

R ound answer to have the same

number of sig. figs. As the

measurement with the leastnumber of decimal places.

Example: 23.456 g + 12.78 g

Line up the decimal point.

Perform the calculation.

R ound to the hundredths place.

Multiplication and Division

R ound answer to the number of 

sig. figs. in the least precise

term in the calculation. 3.24 cm X 12.34 cm=

The answer has 3 sig. figs.

5.44 g ¹ 2.2 ml=

The answer has 2 sig. figs.

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Mathematical operations of Sig. Figs

Addition andSubtraction

Make sure units match

Align decimal point

Perform operation

R ound to units place

farthest to the rightthat is in common to both measurements

Multiplication and

division

Answer has the samenumber of sig.figs. As

the measurement with

the least.