Significant Digits Name __________________ Damon Patterson 4 Period ______ Chem Worksheet 1-6 A measuring device is only able to give a limited amount of information about the object being measured. For example, a balance may only tell the mass of an object to the nearest 0.1 g. Limitations in a measurement are reflected by the number of digits present in the measurement. These digits are known as significant digits. In the example above, an objects mass may be measured as 125.2 g. The measurement has 4 significant digits. It can be difficult to determine the number of significant digits in a measurement when there are zeros, so we will employ a method for ATLANTIC – PACIFIC RULE counting significant 1. Start on correct side – Atlantic (decimal Absent) or Pacific (decimal Present) digits known as the 2. Count digits starting with the first non-zero Atlantic-Pacific rule. 3. Count all digits to the end These rules are outlined in the box to the right. Example How many significant digits are in the numbers 54,000 and 0.000420? 54,000 54,000 has 2 significant digits. We start counting on the Atlantic side (the decimal is absent). We start counting at the first non-zero digit (the four) and count all digits until the end (the five). 0.000720 has 3 significant digits We start counting from the Pacific side (the decimal is present). We start counting at the first non-zero digit (the seven) and count all digits until the end (the last zero). 0.000720 Present Absent Write the number of significant digits present in each of the following measurements. 1. 240 s(2 significant digits) 5. 8520. Pa(4 significant digits) 9. 2.0 g(2 significant digits) 2. 0.003 m(1 significant digits) 6. 8520 Pa(3 significant digits) 10. 75.60 L(4 significant digits) 3. 65.00 mL(4 significant digits) 7. 70 100 kg(3 significant digits) 4. 0.0480(3 significant digits) 8. 0.3006 mol(4 significant digits) 11. 0.000 002 0 km(2 significant digits) 12. 4.20 × 108 mg(3 significant digits) Do the following calculations and round the answer to the correct number of significant digits. 13. 2.15 × (3 significant digits) 14. 0.51 ÷ 0.20(3 significant digits) 15. 15 640 × 3.40(5 significant digits) 16. 0.02 ÷ 0.01568(3 significant digits) 19. 0.0071 + 0.015 + 1.24(4 significant digits) 17. 6520 × 3.45 × 8.1(6 significant 20. 641.1 + 129.34 + 18.154(3 significant digits) digits) 18. 52.18 + 1.7252( 4 significant digits) 21. 5.15 × 103 – 1.2 × 103 (3 significant digits.)