Chapter 1 Understanding the Math in Chemistry

I.What are significant figures/digits? A.Significant figures (digits) are a combination of certain as well as uncertain numbers. B.Example: 48.3 Certain value Estimated (rounded up) (rounded down) This number could have been the result of rounding

1. Any digit that is not zero is significant significant figures significant figures 2. Zeros between non-zero digits are significant significant figures 3. Zeros to the left of the first non-zero digit are not significant significant figures significant figures 4. If the number is greater than one (1), then all zeros to the right of the decimal point are significant significant figures significant figures 5. If the number is less than one, then only zeros that are at the end of the number and between non-zero digits are significant significant figures 6. For numbers that do not contain decimal points, the trailing zeros may or may not be significant. In this course assume the digits are significant unless told otherwise , 2, 3, or 4 significant figures. UNCLEAR assume 4 in calculation significant figures significant figures 7. Assume defined and counted quantities have an unlimited number of significant figures. This is the way I learned the sig. fig. rules

This will not be the way I teach it to you!! Here are two simple rules!! Know them! Rule #1: If a decimal point is present count from Left to Right (L  R) Rule #2: If a decimal point is absent count from Right to Left (L  R) DO NOT START WITH 0 C.Significant Figures RULES

D.Predict the amount of sig. figs in the following: sig. figs sig. fig sig. figs sig. figs sig. figs sig. figs sig. figs sig. fig sig. figs sig. figs.

II.Scientific Notation A.General Equation: M X 10 n 1≤ M <10 n= the number of decimal places moved to get to an acceptable M value +n= greater than 1 -n = less than 1 Examples: Is this an acceptable M? How many places do you have to move the decimal to get to an acceptable M?. Answer:1.387 X Answer:1 X 10 2 # of sig. figs in value must match the # of sig figs in scientific notaion Answer:3.20 X 10 -4

On your own: Answer:5.0 X Answer:8.90 X 10 1 Answer:8.9 X 10 2 Answer:3. 0 X Answer:1 X 10 3 Answer:1.000 X 10 3 Answer:1.05 X 10 4

Going backwards 1.50 X 10 2 Move decimal point to make it larger than X Move decimal point to make it smaller than

Rounding Rules

A.Adding and Subtracting Rounding Rules The answer must contain as many decimal places as the least accurate value (the one with the least # of decimal places) _____ L.a _5.00____

Why do you always round up?? If you stand on the scale and it says: 122.5lbs? Would it be fair to say 123??? I don’t think so!!

B.ODD/EVEN Rule is used when only a 5 is next to the digit you are interested in rounding…… ODD Digit  Round up Even Digit  Leave it alone (EVEN…LEAVIN!!)

Let’s practice rounding to 3 sigs figs = = = = = *round to 1 sig fig

C.Multiplication and Division Rules significant figures The answer must contain as many significant figures as the value with the least number of significant figures

Examples: ( )= /2.4 = / 5.00= (45.2)= How many sig figs?

So what’s the difference between accuracy and precision? Precision refers to how closely individual measurements agree with each other. The repeatability of the results. Accuracy refers to how closely a measured value agrees with the correct value. accurate (the average is accurate) not precise precise not accurate accurate and precise

DENSITY may affect your DESTINY!

Is it a compliment if someone says……You’re DENSE!

According to your understanding…. What’s more dense? A Rock or A Sponge CasanovaKimBaActiveEnglish

Ice Cubes or Liquid Water Ice (H 2 O (s) ) Liquid water (H 2 O (l) ) Water expands 11% when it freezes

Oil   Water Adding water based food coloring

Sumu Wrestler WWE Wrestler Which one is more dense??

Coke v. Diet Coke

Equation for Density The amount of matter in a certain amount of space (volume) Definition for Density D=Mass (g) Volume (ml) or (cm 3 )

Let’s practice some calculations! YEAH