Significant Figures Who cares Sig Figs measure the
- Slides: 35
Significant Figures
Who cares? Sig Figs measure the degree of precision of a measurement.
But first: What’s the difference between accuracy and precision? Do they mean the same thing?
Important definitions: • accuracy: a measure of how closely a measurement agrees with the correct or true value • precision: a measure of how closely individual measurements agree with one another
Example question: 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 sure, plus a digit that is estimated.
For example:
Another example:
Rules for counting sig figs: There are ONLY two rules to remember when counting the # of Sig Figs.
Rule #1: Don’t start counting till you get to a number that isn’t a zero. Rule #2: Once you start counting, don’t stop till you’ve counted all the digits, including zeroes.
And you need to remember a little geography: Where is the Atlantic Ocean, and where is the Pacific Ocean?
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 Pacific side. 273. 5200 Once you start counting, you don’t stop!
Examples 2. 55 0. 2500 100. 25 3 S. F. 4 S. F. 5 S. F.
Examples 12. 50 0. 0003
The first step is always to ask yourself: Is the decimal point present or absent? 18, 000
Answer: Absent Count from first non-zero number moving from the Atlantic side. 18, 000
Examples 135 100 10500 3 S. F. 1 S. F. 3 S. F.
Examples 350 17, 500 135. 0 0. 0020 27. 02 2060
Using sig figs in calculations
For multiplication and division:
Your answer can not be more precise than the least precise measurement.
Think of Sloppy Joe
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. 4 S. F. ? Answer must be recorded as 2 50, 000 cm It can have only one sig fig.
Your answer MUST have the same number of sig figs as the factor with the least number of sig figs.
610 x 6. 20 = 3782 2 S. F. 3 S. F. What is the correct answer? 3800
Example: You calculate the density of an object with mass of 24. 300 grams, and volume of 62. 5 ml. How many sig figs in your answer? D=M/V 24. 300/62. 5 = 0. 3888 Correct Sig. Figs. = 0. 389
For addition and subtraction
Your answer can not contain more decimal places than the least precise measurement.
Line up the decimal points in the numbers. 2. 515 + 1. 3 +12. 00 =? ?
2. 515 1. 3 + 12. 00 15. 815 Answer stops here
Scientific notation
The number of sig figs comes from the number written before the times sign.
Examples 23 10 3. 50 x -4 5. 0 x 10 -4 3 x 10 3 S. F. 2 S. F. 1 S. F.
- When to use sig figs in chemistry
- Significant figures in multiplication
- Significant figures rules
- 87 pg in scientific notation
- When is 0 a significant figure
- Standard deviation precision
- Basic anions
- Stoichiometry sig figs
- How many sig figs are in 5000
- How many significant figures are in the number 176 cm?
- 956 significant figures
- Buret sig figs
- Sig figs addition
- How many sig figs for percent error
- How many sig figs are in .000077?
- What is a significant figure in chemistry
- What are sig
- Sig figs pacific atlantic rule
- Where do sig figs come from
- How many sig figs in 3400
- 3 significant figures
- Caressig
- What is significant figures
- How to get rid of an x exponent
- What are significant figures
- Addition rule of significant figures
- Sig digs rules
- Sig figs
- Operations and scientific notation lesson 5
- Half reduction reaction
- Logarithm significant figures
- How many sig figs are in 7080
- Sig figs rules
- Are all non zero digits significant
- 820 m significant figures
- 654 to 1 significant figure