Download Significant Figits Practice: Rules and Examples and more Slides Chemistry in PDF only on Docsity! CHM 130 Sig Fig Practice Problems Significant digits or figures are not something we make up to terrorize you all semester long. They represent the accuracy of a measurement. For example, a cheap bathroom scale bought at the dollar store reads your weight as 152 pounds, not 152.45809 pounds. It is not that accurate. Significant digits are very important in all measurements. Now remember that conversion factors such as (1 L / 1000 mL) or (1 foot = 12 inches) DO NOT affect the significant digits because they are exact numbers or definitions. A. Rules - note that # means a non-zero digit (123456789) 1. Digits 1 to 9 always count 2. Zeros in front never count 3. Zeros after a # do not count unless they are also after a decimal place 4. Zeros in between any digits that count, count also B. Examples 1. 2040 - 3 sig fig 2. 2040.0 - 5 sig fig 3. 00204.0 - 4 sig fig 4. 0.00204 - 3 sig fig 5. 0.020400 - 5 sig fig 6. 2.0400 - 5 sig fig 7. 100,000 - 1 sig fig 8. 100,000.0 -7 sig fig 9. 0.0001 - 1 sig fig 10. 0.000100 - 3 sig fig C. When multiplying or dividing, the answer must have the same number of sig fig as the least sig fig in the problem. Your answer can not be more accurate than any measurement in the problem. It is kinda like the weakest link in the problem dictates how accurate the answer can be. D. When adding or subtracting the answer must have the same number of decimal places as the least number of decimal places in the problem. Your answer can not be more accurate than any measurement in the problem. E. Example: Pretend we weigh something on a cheap scale, and it is 3.5 grams. Then we weigh something else on a scientific scale and it is 4.2448 grams. If we add them together the answer is 7.7 grams because we can only have one decimal place. F. Now pretend we multiply 2.569 inches by 1.7 inches. Answer is 4.4 in2 because the least amount of sig fig was 2 sig fig so the answer can only have 2 sig fis. Also, inch x inch = inch squared! G. Now remember that conversion factors such as (1 L / 1000 mL) DO NOT affect the significant digits because they are exact numbers. Any such equality will not dictate the sig figs in your final answer. H. More examples: 1. 3340 ft x 1.2 ft = 4.0 x 103 ft2 The answer must have 2 sig dig cause of the 1.2 thus 4000 is incorrect because it only has 1 sig dig. 2. 88359 m2 / 3 m = 30,000 m The answer can only have 1 sig dig cause of the 3. 3. 8.888 m x 3.29853 m = 29.32 m2 The answer must have 4 sig dig like 8.888. 4. 1.25 mm + 3.2 mm = 4.5 mm The answer can only have one decimal place like the 3.2. 5. 145 L - 0.222 L = 145 L The answer cannot have any decimal places cause 145 has none. 6. 145 g - 0.99 g = 144 g The answer cannot have any decimal places. 7. 0.042 m + 1.33 m = 1.37 m The answer can have only 2 decimal places like 1.33.
