cheat sheet for chemistry, Cheat Sheet of Chemistry

Download cheat sheet for chemistry and more Cheat Sheet Chemistry in PDF only on Docsity! Chemistry: Significant Digits Name__________________________ Hr____ Date __________ In an attempt to get away from the mathematical burden of uncertainties, scientists have gone to the use of established rules for significant digits that have greatly simplified calculations. These rules are: 1. Significant numbers are always measurements and thus should always be accompanied by the measurement's unit. For simplicity, units are not included in the following examples. 2. Any numbers (that are measurements) other than zero are significant. (Many times the zeros are also significant as you will see below.) Thus 123.45 contains five significant digits. 3. Any zeros between numbers are significant, thus 1002.05 contains six significant digits. 4. Unless told differently, all zeros to the left of an understood decimal point (a decimal that is not printed) but to the right of the last number are not significant. The number 921000 contains three significant digits. 5. Any zeros to the left of a number but to the right of a decimal point are not significant. 921000. has six significant digits. 6. These zeros are present merely to indicate the presence of a decimal point (they are used as place holders), (these zeros are not part of the measurement). The number 0.00123 has three significant digits. The reason that these zeros are not significant is that the measurement 0.00123 grams is equal in magnitude to the measurement 1.23 milligrams. 1.23 has three significant digits, thus 0.0123 must also have three significant digits. 7. Any zeros to the right of a number and the right of a decimal point are significant. The value 0.012300 and 25.000 both contain five significant digits. The reason for this is that significant figures indicate to what place a measurement is made. Thus the measurement 25.0 grams tells us that the measurement was made to the tenths place. (The accuracy of the scale is to the tenths place.) Give the number of significant digits in each of the following measurements: 1. 1278.50 __________ 7. 8.002 __________ 13. 43.050 __________ 2. 120000 __________ 8. 823.012 __________ 14. 0.147 __________ 3. 90027.00 __________ 9. 0.005789 __________ 15. 6271.91 __________ 4. 0.0053567 __________ 10. 2.60 __________ 16. 6 __________ 5. 670 __________ 11. 542000. __________ 17. 3.47 __________ 6. 0.00730 __________ 12. 2653008.0 __________ 18. 387465 __________ Round off the following numbers to three significant digits: 19. 120000 _______________ 22. 4.53619 _______________ 20. 5.457 _______________ 23. 43.659 _______________ 21. 0.0008769 _______________ 24. 876493 _______________ How many significant figures are in each of the following numbers? 1) 5.40 ____ 6) 1.2 x 103 ____ 2) 210 ____ 7) 0.00120 ____ 3) 801.5 ____ 8) 0.0102 ____ 4) 1,000 ____ 9) 9.010 x 10-6 ____ 5) 101.0100 ____ 10) 2,370.0 ____ 11) Why are significant figures important when taking data in the laboratory? 12) Why are significant figures NOT important when solving problems in your math class? 13) Using two different instruments, I measured the length of my foot to be 27 centimeters and 27.00 centimeters. Explain the difference between these two measurements. 14) I can lift a 20 kilogram weight over my head ten times before I get tired. Write this measurement to the correct number of significant figures.