U00 L02PS - Significant Figures v06.ppt

7/27/2019 U00 L02PS - Significant Figures v06.ppt

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Mr. Shields Regents Chemistry U00 L02


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Significant Figures

In all numbers there are digits that are Significant

& others are not Significant.

Why should we be concerned which

numbers are significant?

1) Measurements are never exact.

2) Scientist want to record their data (nos.) with the

LEAST AMOUNT OF UNCERTAINTY.


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Significant Figures

Scientists created rules so numbers could be writtenwith the least amount of uncertainty. These are therules governing what are called Significant figures.

By using these rules scientist can be confident that the

numbers people report dont exaggerate their accuracy!

The greater the number of significant figures the more

PRECISE the number

For example 3.41 is less precise than 3.413341

There are more sig figs in the 2ndnumber


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Significant Figures

To determine the number of significant figures in a number

Lets take a look a technique that will help us figure it out

Its called the ATLANTIC - PACIFIC RULE


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Atlantic Pacific Rule

1. Draw a map of the United States and labelthe 2 oceans which are???

PACIFIC ATLANTIC


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Atlantic Pacific Rule1. If a decimal point is Present in the number

start counting from the Pacific side

2. If a decimal point is Absent in the numbercount from the Atlantic side

3. Begin counting all numbers from the first

NON-ZERO digit

- That number and all digits after it

(including zeros) are SIGNIFICANT


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0.06901

100,100,300

Try the rule with these two numbers. How many

Sig figs are there?


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Significant Figures

Lastly, all COUNTING and DEFINED NUMBERS are

treated as if they have an INFINITE no. of Sig Figs

Ex: 2 pairs of gloves Counting (infinite sig fig)

7 Keys Counting

2.54 cm = 1 inch Definition


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Lets try some examples. How many significant

Figures are in the following numbers?

3456 4 sig figs

0.040860 5 sig figs

3.50001 6 sig figs

20000 1 sig fig

7 oranges Infinite sig figs


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Lets try some more examples. How many sig figs

Are there in the following pairs of numbers?

750 vs. 750. 2 vs 3 sig figs

1001 vs. 1000 4 vs. 1 sig figs

2.07 vs. 2.070 3 vs. 4 sig figs

0.00572 vs 572 3 vs. 3 sig figs

1001. vs. 1000. 4 vs 4 sig figs


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Working with Significant Figures

Its important we know how to manipulate Significant

figures. Well need to know the same manipulations

we needed to know for Scientific Notation, namely:

1. Addition +

3. Multiplication x

4. Division /

2. Subtraction -


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Lets look at the rules that govern these mathematical

operations.

1 & 2. Addition & Subtractionhave the same rule

The number of decimal places in the Ans. EQUALS the

Smallest Number of DECIMAL places in any of the nos.

Being added or subtracted.

Ex: 6.8 + 11.934 = 18.734

= 18.7

2.01 + 0.003 + 1 = 3.013= 3


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3 & 4. Multiplication & Divisionhave the same rule

The number of sig figs in the ans. Equals the number of

Sig Figs in the least precise number

Ex: 6.8 x 11.934 = 81.1512

= 81.

2.014 / 0.70 = 2.877143

= 2.9

Documents

U00 L02PS - Significant Figures v06.ppt