Rules for Significant Figures

Transcription

1 Name AP Chemistry Sig Fig Packet Rules for Significant Figures The following applies for numbers that are measured: 1) All non-zero digits in a number are significant. a. A non-zero digit is any digit not zero: 1,2,3,4,5,6,7,8, and 9. 2) All leading zeros are not significant. a. Leading zeros are the zeros in front of a number (on the left side). For example, the number has 3 leading zeros in front of 236. These zeros are not significant. 3) Trailing zeros are significant only if a decimal point is present somewhere in the number. a. Trailing zeros are the zeros at the end of a number (on the right side). For example, the number 2000 has 3 trailing zeros. b. For example, the zeros in 25.0 and are significant because a decimal point is present in both cases. c. The zeros in 350 and 1000 are not significant because a decimal point is not present in both cases. d. The trailing zeros in and 800. are significant because a decimal point is present in both cases. 4) Any zero between two other significant digits is always significant. a. For example, all of the zeros in 801 and are significant. 5) A line over a zero indicates that it is significant. _ a. For example, there are 3 sig figs in The last zero (in the ones place) is not significant. 1

2 6) When multiplying or dividing, the answer will have the same amount of sig figs as the value with the least number of sig figs. If the answer has too many decimal places, round to the number of sig figs it should have. a. For example, 12 / 3.00 = i. 12 has two significant figures and 3.00 has three, so the answer should only have two. b. For example, 3.20 x 5.04 = i. The starting values only have three significant figures each, so round the answer to three significant figures, ) When adding and subtracting values, find the smallest decimal place that all values have in common and are significant and that is the last significant decimal place in your answer. Add the values like normal and round to the significant decimal place. c. For example, 5.23 (significant to hundredths place) (significant to thousandths place) i. The answer is limited to the hundredths place because 5.23, so the answer is rounded to 8.72 (hundredths place). d. For example, 1050 (significant to tens place) -326 (significant to ones place) i. The answer is limited to the tens place because of 1050, so the answer is rounded to 720 (tens place). 8) When performing a calculation that involves only multiplication or division, do the whole calculation and round at the end. Do not do any intermediate rounding. 9) When performing a calculation that involves only addition or subtraction, do the whole calculation and round at the end. Do not do any intermediate rounding. 10) When performing a calculation that involves both multiplication or division and addition or subtraction, you must round in between steps. That is, you must round between moving from a multiplication or division step to an addition or subtraction step. 2

3 Practice: Determine the number of significant figures in the following measurements. 1) m 2) 900 ml 3) 1.00 ms 4) 3.50 g 5) 5009 mm 6) 40.0 L 7) 300. mg 8) cm 9) km 10) 0.3 s 11) ml 12) g 13) m 14) 173 ms 15) kg 16) s 17) 1000 m 18) m 19) 1000 m 20) g 21) ms 22) 34,500 mg 23) cm 24) mm 25) 20,005 kg 26) 680 g 27) s Rules for rounding When making calculations with measured values, the answer will need to be rounded to the correct number of significant figures according to the following rules. 1) Round down whenever the digit following the last significant figure is a 0,1,2,3, or 4. a. For example, becomes ) Round up whenever the digit following the last significant figure is a 6,7,8,9 or a 5 with any nonzero digit at any place after it. a. For example, becomes b. For example, round to the tenths place becomes ) If the digit following the last significant figure is a 5 with either zeros or nothing after it, round to the even number. a. For example, rounded to the tenths place becomes The value is rounded up to the even number. b. For example, becomes The value is rounded down to the even number 6 instead of up to 7. 3

4 Practice: Round the value to the given number of significant figures (SF) ; 2 SF ; 2 SF ; 2 SF ; 3 SF ; 3 SF ; 2 SF ; 2 SF ; 3 SF ; 4 SF ; 2 SF ; 2 SF ; 1 SF ; 4 SF ; 2 SF ; 3 SF ; 3 SF ; 3 SF ; 3 SF ; 1 SF ; 4 SF ; 1 SF ; 3 SF ; 2 SF ; 4 SF ; 3 SF ; 1 SF ; 2 SF ; 4 SF 4

5 Sig Fig Practice Measure the following lines with a ruler, record the length in cm, and determine the number of sig figs. 1. Length: 2. Length: 3. Length: Determine the number of sig figs in the following numbers ,542, x x First, write down how many significant figures are in each number. Next, perform the calculation, writing down the unrounded answer. Then, write the answer rounded to the correct number of significant figures: 5

6 x / / x x x x / x / x x x (5.20 x 0.67) / Measure the following rectangle with a ruler, record the length and width in cm, and determine the number of sig figs. Then, calculate the area rounding the answer to the correct number of sig figs. 6

7 Length: Width: Area: Scientific Notation Practice Write the following numbers in scientific notation. (NO SIG FIGS HERE) 1) 61,050 2) ) 90,100,000 4) 300,000 5) ) ) 340,000,000 8) 670 9) ) Write the following numbers in long form. (NO SIG FIGS HERE) 11) x ) x ) 6 x ) x ) 4.42 x

8 16) 1.09 x ) 3.5 x ) 7.6 x ) x ) 9.2 x 10-1 Perform the following calculations using your calculator. Write the answer in proper scientific notation. (USE SIG FIGS HERE) 21) (3 x 10 6 )(2 x 10-6 ) 22) (4 x 10-2 )(1.5 x 10 9 ) 23) (8.0 x 10 3 ) / (4.0 x 10-7 ) 24) (3.0 x 10 4 ) / (2.00 x 10 5 ) 25) (6.0 x 10 5 )(2.0 x 10 3 ) 8