Welcome to Chemistry! Sept 11, 2015 Friday

Transcription

1 Welcome to Chemistry! Sept 11, 2015 Friday DO NOW: How many sig figs in this number? Round this number to 3 sig figs Objectives: 1. Quantitative Tools for Chemistry: complete calculations using factor analysis, S.I. Units, Scientific Notation and demonstrate use of Significant Figure Rules. Agenda: Syllabus Topic of the day Go through IMPORTANT RULES HANDOUT: scientific notation, math operations with sig figs. Rally coach assignment Homework Scientific Calculator due as an assignment today Friday September 5th Things Due Monday: September 14 th Dedicated Spiral Notebook for this class Quiz on Sig Fig and rounding HW1 Due Tuesday Sept 15 th

2 Syllabus Topic of the day...

3 Procedure of the day Classroom discussion Don t put down others keep it professional like a job Raise your hand to get called on. Ask questions if you don t understand!!! Very important!!! YOU WILL have questions!

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5 Add this to your IMPORTANT RULES HANDOUT General RULES FOR ROUNDING: 1. If it is less than 5, drop it and all the figures to the right of it. 2. If it is 5 or more then, round the preceding figure up.

6 Example #1 Suppose you wish to round to four significant figures. Look at the fifth figure. It is a 4, a number less than 5. Therefore, you will simply drop every figure after the fourth, and the original number rounds off to

7 Example #2 Round to three significant figures. Look at the fourth figure. It is 7, a number greater than 5, so you round the original number up to 3.79.

8 Example #4 Round to three significant figures. Look at the fourth figure. It is a 5 with other digits following.so since the value is greater than 5, round the preceding figure up and drop the rounded digits. The number becomes 24.9

9 Example 5: Here are some more examples of the "five rule." Round off at the underlined number

10 Example 5: Here are some more examples of the "five rule." Round off at the five (3.08) 3.85 (3.9) (22.74) (0.0057) (2.050)

11 Scientific notation and using Sig Fig in calculations On your paper discuss and write down actual numbers estimates for your answer: How many cells are there in the human body? How big is a virus in meters? 50,000,000,000, trillion (smaller person) to 75,000,000,000, trillion(bigger person) cells meters How many cells are in 3 people (one bigger and 2 smaller)? How long would a parade of 4 viruses be?

12 Using numbers in science In on paper How many cells are there in the human body? (smaller person) to 75,000,000,000(bigger person) cells How big is a virus in meters? meters How many cells are in 3 people (one bigger and 2 smaller)? 50,000,000, ,000,000,000+75,000,000,000 = 175,000,000,000 How long would a parade of 4 viruses be? m m m = m

13 Scientific Notation Do you know this number, 300,000,000 m/sec.? It's the Speed of Light! Do you recognize this number, kg.? This is the mass of a dust particle! Scientists have developed a shorter method to express very large and small numbers. This method is called scientific notation. Scientific Notation is based on powers of the base number 10. The number 123,000,000,000 in scientific notation is written as : 1.23 x The first number 1.23 is called the coefficient. It must be greater than or equal to 1 and less than 10. The second number is called the base. It must always be 10 in scientific notation. The base number 10 is always written in exponent form. In the number 1.23 x the number 11 is referred to as the exponent or power of ten.

14 Scientific Notation Scientific Notation only represents the significant figures, so before you convert you must determine which values are significant or where to round your answer. To determine the exponent power of ten, count the number of decimal places from the original number to the scientific notation form If the number is greater than 10 it will have a positive exponent (big numbers are positive exponents) If the number is smaller that 1 it will have a negative exponent (little numbers are negative exponents) Example: 25,120, x x 10-3

15 Practice 602,000,000,000,000,000,000, ,000

16 Practice 602,000,000,000,000,000,000, x x x x , x 10 5

17 More Practice , ,

18 More Practice x , x x , x x 10-6

19 Addition Subtraction Rules for Sig. Figs. Adding and Subtracting: Add or Subtract using your calculator, and round the answer to the least accurate decimal place = => 17.9 the tenths place in 0.1 is the least accurate decimal place. Think about adding several objects together that were weighed with different devices. It is not fair or accurate to report the total weight of all the objects with any more accuracy then the scale that reports the least number of decimal places

20 RallyCoach Partners take turns, one solving a problem while the other coaches. Partner A solves the first problem Partner B watches and listens, checks, coaches if necessary, and praises. Partner B solves the next problem Partner A watches and listens, checks, coaches if necessary, and praises. Partners repeat taking turns solving successive problems.

21 +/- with Sig Figs 1a = b = a = b , = a =

22 +/- with Sig Figs 1a = b = a = b , = a =

23 More +/- with sig figs = = = = =

24 More +/- with sig figs 3b = a = b = a = b =

25 More +/- with sig figs 3b = a = b = a = b =