Measurement Day 1 – Sig Figs
Significant Figures (SIG FIGS) 7.0 does not equal 7.00 in chemistry class If your lab partner has 5.50 cm as an answer and you have 5.5 cm, one of you will not earn credit!! In Science 5.50 cm does not equal 5.5 cm
Significant Figures (SIG FIGS) 1. Rule All non-zero digits are significant 143 has 3 significant digits 1,276 has four significant digits
Significant Figures (SIG FIGS) 2. Rule Leading Zeros – NEVER significant 0.000067 Middle Zeros – ALWAYS significant 101 Trailing Zeros – SOMETIMES significant Depends on a decimal point If decimal is present then they ARE significant If decimal is not present then they ARE NOT significant
Practice 23.50 402 5280 0.080
A Memory Trick – The USA Pacific Atlantic Start at the left and stop at the first non-zero. 0.03560 That # and everything after it is significant!! ____ sig figs Atlantic Start on the right and stop at the first non-zero. 3500 That # and everything after is are significant! ____ sig figs
Significant Digits (13.91)(23.3) = 324.103 324 Calculating with Significant Digits Multiply/Divide – Your answer should be equal to the number of significant digits in the least accurate factor. This is the one with the fewest sig figs (13.91)(23.3) = 324.103 4 SF 3 SF 3 SF 324
Significant Digits 224 g + 130 g 354 g 224 g + 130 g 354 g 3.75 mL Calculating with Significant Digits Addition and Subtraction – Your answer should be simplified according to the number with the fewest decimal places 224 g + 130 g 354 g 224 g + 130 g 354 g 3.75 mL + 4.1 mL 7.85 mL 3.75 mL + 4.1 mL 7.85 mL 350 g 7.9 mL
When performing calculations, you should do the calculation using all the digits allowed by the calculator and round off only at the END of the problem!!
Significant Digits 2. 18.9 g - 0.84 g 18.06 g Practice Problems 1. (15.30 g) ÷ (6.4 mL) = 4 SF 2 SF = 2.390625 g/mL 2.4 g/mL 2 SF 2. 18.9 g - 0.84 g 18.1 g 18.06 g
Significant Digits 4. 1.942 + 26.93 28.872 Practice Problems 3. (12000) x (1.53) 2 SF 3 SF = 18360 18000 4. 1.942 + 26.93 28.87 28.872