Rules for Using Significant Figures in Mathematical Operations



Name ___________________________________ Chemistry

Mr. Harper

Sig Fig Packet

Measurement Unit Study Guide

1. Significant figures and measurements

a. What is the difference between accuracy and precision? Why are both important in science?

b. What is a significant figure, and what are they used for?

c. How do you determine the number of sig figs in a number or measurement?

d. How do you round to the correct number of sig figs when multiplying, dividing, adding, or subtracting?

e. How do you precisely read a triple beam balance, ruler, graduated cylinder, etc.?

2. Scientific notation

a. How do you convert a number into scientific notation and vice versa?

b. How do you multiply and divide numbers in scientific notation?

3. Conversion factors

a. How do you convert from one unit to another?

4. The mole

a. What is the mole, and how do chemists use it?

b. What is Avogadro’s number?

c. What is the molar mass of an element?

d. How do you convert among atoms, moles, and grams of an element?

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 0.00236 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 1.300 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 0.00420 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 10.05 are significant.

5) A line over a zero indicates that it is significant.

_

a. For example, there are 3 sig figs in 3500. The last zero (in the ones place) is not significant.

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 = 4 ( 4.0

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 = 16.128 ( 16.1

i. The starting values only have three significant figures each, so round the answer to three significant figures, 16.1.

7) 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)

+ 3.484 (significant to thousandths place)

8.714 ( 8.71

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)

724 ( 720

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.

Practice: Determine the number of significant figures in the following measurements.

1) 0.0042 m _____

2) 900 mL _____

3) 1.00 ms _____

4) 3.50 g _____

5) 5009 mm _____

6) 40.0 L _____

7) 300. mg _____

8) 20900 cm _____

9) 102.0 km _____

10) 0.3 s _____

11) 0.056 mL _____

12) 800.01 g _____

13) 0.0840 m _____

14) 173 ms _____

15) 1.5000 kg _____

16) 6.70001 s _____

17) 1000 m _____

18) 1000. m _____

19) 1000 m _____

20) 0.00007 g _____

21) 1000.00 ms _____

22) 34,500 mg _____

23) 0.00302 cm _____

24) 0.02070 mm _____

25) 20,005 kg _____

26) 680 g _____

27) 540.0 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, 30.24 becomes 30.2.

2) 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, 22.49 becomes 22.5.

b. For example, 54.7511 round to the tenths place becomes 54.8.

3) 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, 79.3500 rounded to the tenths place becomes 79.4. The value is rounded up to the even number.

b. For example, 32.65 becomes 32.6. The value is rounded down to the even number 6 instead of up to 7.

Practice: Round the value to the given number of significant figures (SF).

1. 8.37; 2 SF

2. 14.8; 2 SF

3. 1.4751; 3 SF

4. 0.0765; 2 SF

5. 285.35; 4 SF

6. 10.1; 2 SF

7. 0.82396; 4 SF

8. 120.4; 3 SF

9. 51382.4; 3 SF

10. 4.500; 1 SF

11. 1980; 1 SF

12. 173; 2 SF

13. 17.4297; 3 SF

14. 23187; 2 SF

15. 0.427; 2 SF

16. 1.7990; 3 SF

17. 13.5; 2 SF

18. 128.5; 3 SF

19. 3.45; 2 SF

20. 3.50001; 1 SF

21. 1850; 2 SF

22. 21.58; 3 SF

23. 3.7148; 3 SF

24. 116.0503; 4 SF

25. 2554.6; 3 SF

26. 12.425; 4 SF

27. 0.025801; 1 SF

28. 14.69501; 4 SF

Name _________________________ Chemistry

Pd _____ Mr. Harper

Sig Fig Practice

Measure the following lines with a ruler, record the length in cm, and determine the number of sig figs.

1.

Length: _________________ # of sig figs: ______________

2.

Length: _________________ # of sig figs: ______________

3.

Length: _________________ # of sig figs: ______________

Determine the number of sig figs in the following numbers.

4. _____1.37

5. _____378.42

6. _____6.022

7. _____8.470932

8. _____270.

9. _____6,542,000

10. _____100.

11. _____100

12. _____37.0

13. _____37

14. _____142.00

15. _____0.0021

16. _____0.03987

17. _____0.000670

18. _____0.030900

19. _____5.00

20. _____8 x 10-6

21. _____3.50 x 105

22. _____8200

23. _____8200

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:

1. 4.5 x 6.75

2. 3.0 / 2.3

3. 99.00 / 33

4. 70 x 3

5. 8.4 x 310

6. 0.43 x 1.69

7. 200 x 1.47

8. 3.940 / 3.70

9. 3.78 x 6.8

10. 8.51 / 30.10

11. 0.4080 x 1690

12. 200. x 0.071

13. 1000 x 3.000

14. (5.20 x 0.67) / 4.100

15. 110 + 63

16. 92 + 75

17. 1.45 – 0.566

18. 3000 – 800

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.

Length: _________________ # of sig figs: ______________

Width: _________________ # of sig figs: ______________

Area: __________________

Name _________________________ Chemistry

Pd _____ Mr. Harper

Measurement Practice

Wooden Block

1. Measure the length, width, height of the wooden block to the smallest division of the ruler.

a. Length = ___________ cm # of sig figs: __________

b. Width = ____________ cm # of sig figs: __________

c. Height = ____________ cm # of sig figs: __________

2. Calculate the volume in cubic centimeters and round to the correct number of sig figs.

a. Volume = length x width x height = ________________cm3

3. Measure the mass on the triple beam balance to the smallest division.

a. Mass = ______________ g # of sig figs: ___________

4. Calculate the density in g/cm3 and round to the correct number of sig figs.

a. Density = mass / volume = __________________ g/cm3

Cylinder

5. Measure the diameter and height of the cylinder to the smallest division and calculate the radius.

a. Diameter = __________ cm # of sig figs: ___________

b. Height = ____________ cm # of sig figs: ___________

c. Radius = ____________ cm # of sig figs: ___________

6. Calculate the volume in cm3 and round to the correct number of sig figs.

a. Volume = 3.14 x (radius)2 x height = ________________ cm3

7. Verify the volume measurement using the graduated cylinder. Volume = ______________ mL

8. Measure the mass in grams to the smallest division.

a. Mass = ______________ g # of sig figs: ___________

9. Calculate the density in grams / cubic centimeter and round to the correct number of sig figs.

a. Density = mass / volume = ____________________ g/cm3

Name ________________________ Chemistry

Mr. Harper

Scientific Notation Practice

Write the following numbers in scientific notation.

1) 61,050 _________________________

2) 0.0000809 _________________________

3) 90,100,000 _________________________

4) 300,000 _________________________

5) 0.075 _________________________

6) 0.000365 _________________________

7) 340,000,000 _________________________

8) 670 _________________________

9) 0.251 _________________________

10) 0.000000047 _________________________

Write the following numbers in long form.

11) 2.089 x 10-4 _________________________

12) 3.301 x 105 _________________________

13) 6 x 102 _________________________

14) 5.990 x 10-3 _________________________

15) 4.42 x 107 _________________________

16) 1.09 x 104 _________________________

17) 3.5 x 10-5 _________________________

18) 7.6 x 10-2 _________________________

19) 5.990 x 106 _________________________

20) 9.2 x 10-1 _________________________

Perform the following calculations using your calculator. Write the answer in proper scientific notation.

21) (3 x 10 –6)(2 x 10-6)

22) (4 x 10-2)(1.5 x 109)

23) (8.0 x 103) / (4.0 x 10-7)

24) (3.0 x 104) / (2.00 x 105)

25) (6.0 x 105)(2.0 x 103)

26) (2.0 x 104)(4.00 x 10-8)

27) (5.0 x 103) / (8.0 x 106)

28) (2.00 x 10-4)2

29) (7.5 x 10-3)(2 x 106) / (3.0 x 10-4)

30) (5.00 x 10-3)3

31) (4.83 x 10-5) / (9.2 x 10-7)

32) (8.89 x 106)(4 x 10-3)

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download