Do Now

• Take out homework packet, do #1 on page 19

Measurement Quiz

Tonight's Homework

• Read page 9-10 for the next topic• Homework Packet p 19+20• Watch Rosengartens video (1.03 rounding)

and take a look at the homework (3). • Write down at least 2 questions to ask for the

next class. There will be questions on the daily quiz from the reading

(15 minutes)

Todays Goal

• Be able to determine a numbers precision and the number of significant figures

• Take out your note packets and turn to page 7

What the heck are significant figures?

• Good question……• Significant = important• Figures = numbers• Aren’t all numbers important?– Not always

Significant vs. Insignificant

• Numbers we know for sure from measurement are significant– Numbers that we don’t know are not

• Example: • 13.5 ml– Precision was to the tenths, so we know all of those

numbers for sure• 210 g– Our precision stopped at the 1 in the tens place– We don’t know what the zero is so it is not significant

Significant vs. Insignificant

• 00031 g– Do the zeros to the left count for anything?• No, they are insignificant

• Zeros to the LEFT of the first integer are insignificant

• .00073 l– The 7 and 3 are significant.

Determining the number of Sig figs

• 1) Look at the number• 2) Determine what the precision is• 3) Count from the left to the right, starting

with the first non-zero and ending at the precision

• 132.1 g

NumberDoes it have a decimal?

Yes No

Precision is farthest # on right

Precision is right most non-zero or a zero w/a line over it

Count from the left most non-zero

to the precision

What is precision?

• Being exact and accurate

2) Rosengartens rules for determining precision

• How numbers are written will tell you the precision of the number

• 1) If the measurement has a decimal point in it, the precision is the place furthest to the right in the measurement

• Ex: 23.004 cm– Precision is to the thousandths

More examples

• 0.3320 g– Ten thousandths

• 330. mL– Ones

If the measurement does not have a decimal point in it…

• The precision is the place where either the rightmost integer is, or where a zero with a line over it is (p8)

• 2300 km– Hundreds

More Examples

• 1700 g• 1,000,000 joules• 17 ml• 10 ml

Rosengarten’s Rule for Sig Fig’s• The number of significant figures in a

measurement equals the total number of digits from and including the first (leftmost) integer in the measurement all the way to the limit of precision of that measurement.

• Ex; 23.285 cm– Precision is to the…….. – Thousandths….so how many sig figs?– 5!

To the tune of “To the left”

• To the left, to the left, start counting at the first non-zero to the left

• Count To the right till you reach the precision

3100 m

• So how many sig figs?• 3100 m precision ends at the #1• Count from the first non-zero on the left, to

the precision….• 2 sig figs

What about 3100. m?

• Oooo, a decimal point! What does that mean for the precision?

• 3100. Precise to the 0 in the ones place• Count from the first non-zero on the left to the

precision….• 4 sig figs!

What if it was a small number?

• Lets say; 0.09053 kJ• Precision is to the…..hundred thousandths• .09053 kJ• Count from the first non-zero number on the

left (9) to the precision. How many sig figs?• 4 sig figs!

Wait, why ignore the 0 in the tenths?

• Its kind of like all the 0’s that are to the left of any number.

• 3200 m could be written 000003200 m• The zeros to the left of the first number are

insignificant

Ex: 0.050600 mol

• Precision?– Millionths place; 0.050600

• First non-zero number; 0.050600• Total number of sig figs?• 5

Practice: How many sig figs

• 2310. g• .09 km• 2300.100 J• 3.14 mg• 56.364327 L

Cool

• Take this time to do your homework (#2, p 19-20) and have me check it

• YOUR HOMEWORK FOR TONIGHT• Read page 9-10 for the next topic, watch

Rosengartens video (1.03 rounding) and take a look at the homework (3). Write down at least 2 questions to ask for the next class. There will be questions on the daily quiz from the reading

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