Guided notes on Accuracy, Precision, and significant ...



Guided Notes: Accuracy, Precision, and significant figures (aka “sig figs”)

Who cares? Sig Figs measure the degree of _________ of a

measurement.

But first: What’s the difference between accuracy and precision?

Do they mean the same thing?

Two students measured the mass of a small pebble, which had an actual mass of 2.35 grams.

Sally’s measurements were 2.78 grams, 2.82 grams, and 2.81 grams.

Madison’s measurements were 2.30 grams,

2.34 grams, and 2.41 grams.

Which student was more accurate?

Which student was more precise?

A correctly precise measurement includes all digits

that are known for ______, plus a digit that is _____________.

For example, what is the length of the above object in inches? ________in.

What is the volume of the liquid in the above 3 graduated cylinders in mL?

From L ( R, 1st cylinder = ____; 2nd cylinder = ____; 3rd cylinder = ______

There are ONLY two rules to remember when counting

the # of Sig Figs.

Rule #1: Don’t start counting ______ you get to a number that isn’t a _______.

Rule #2: Once you ________ counting, don’t stop till you’ve counted ____ the ______, including ______.

Next, you need to know some geography. On what side of the U.S. is the Pacific Ocean, left or right? ______On what side of the U.S. is the Atlantic Ocean, L or R? _________

How many sig figs are in this number: 273.5200?

Ask yourself:

Is the decimal point present or absent? Answer: Present

Count from first non-zero number starting at the P________ side. _____ sig figs

Examples: 2.55 = _____ sig figs; 0.2500 = ______ sig figs; 100.25 = ______ sig figs

More examples: 12.50 = _____ sig figs; 0.0050 = ____ sig figs; 0.0003 = ____ sig figs

The first step is always to ask yourself:

Is the decimal point present or absent?

18,000,000

Answer: Absent; Count from first non-zero number moving from the A_______ side.

= _____ sig figs

Examples: 135 = _____ sig figs; 100 = _____ sig figs; 10,500 = ____ sig figs

More examples: 350 = ___ sig figs; 17,500 = ____ sig figs; 135.0 = ___ sig figs

0.0020 = ___ sig figs; 27.02 = ____ sig figs; 2060 = ____ sig figs

For multiplication and division: you answer can not be more precise than the least precise measurement. Think “ _________ ____”. You and your lab partner, Sloppy Joe, have been assigned to find the area of your lab table. You carefully measure the length, and find it to be 233.65 cm. Sloppy Joe casually slides the meter stick along the width, suggests that it measures about 200 cm.

233.65 x 200 = 46730

(5 s.f.) (1 s.f.)

Answer must be recorded as 50,000 cm2

It can have only one sig fig. Your answer MUST have the same number

of sig figs as the factor with the _________ number of sig figs.

610 x 6.20 = 3782

(__ s.f.) x (___ s.f.)

What is the correct answer? _______

**The rule for addition and subtraction is different; you won’t have to memorize that one.

However you will need to know the rules on scientific notation and sig figs. The number of sig figs comes from the number written ________ the times sign.

3.50 x 1023 = ___ sig figs; 5.0 x 10 -4 = ___ sig figs; 3 x 10-4 = ____ sig figs

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