CHAPTER 3 SCIENTIFIC MEASUREMENT 3 1 OBJECTIVES Convert

CHAPTER 3 SCIENTIFIC MEASUREMENT

3. 1 OBJECTIVES Convert measurements to scientific notation. Distinguish among accuracy, precision, and error of a measurement. Determine the number of significant figures in a measurement and in a calculated answer. 3. 1 - Measurements and Their Uncertainty

Using and Expressing Measurements are fundamental to the experimental sciences. For that reason, it is important to be able to make measurements and to decide whether a measurement is correct. MEASUREMENT is a quantity that has both a number and a unit. KEYWORD- Measurement

The most important thing to remember is……. Chemists are lazy. …. like really lazy I’m not kidding, we are super lazy.

This is why we have Scientific Notation allows a given number to be written as the product of two numbers. For example: 5, 674, 000, 000 would be written as 5. 674 x 1021 KEYWORD- Scientific Notation

Practice Problems CONVERT THE FOLLOWING INTO SCIENTIFIC NOTATION 1 - 3, 400 2 - 0. 000023 3 - 101, 000 4 - 0. 010 5 - 45. 01 6 - 1, 000 7 - 0. 00671 8 - 4. 50

Practice Problems #2 CONVERT THE FOLLOWING NUMBERS INTO STANDARD NOTATION 1 - 2. 3 x 104 2 - 1. 76 x 10 -3 3 - 1. 901 x 10 -7 4 - 8. 65 x 10 -1 5 - 9. 11 x 103 6 - 5. 40 x 101 7 - 1. 76 x 100 8 - 7. 4 x 10 -5

Accuracy, Precision, and Error

Putting it into exact terms… Accuracy is a measure of how close a measurement comes to the actual or true value of whatever is measured. Precision is a measure of how close a series of measurements are to one another. KEYWORDS- Accuracy and Precision

How do we use these two measurements? To evaluate the accuracy of a measurement, the measured value must be compared to the correct value. To evaluate precision of a measurement, you must compare the values of two or more repeated measurements.

Determining Error Lets face it, making exact measurements in lab is difficult. And since nobody is perfect, except Mr. P, you’re going to make mistakes. The important thing is making sure you calculate how much you messed up.

How to calculate error… Accepted value, which is the correct value based on reliable references. Experimental value is the value measured in the lab. The difference between the accepted and experimental values is called error. KEYWORDS- Accepted Value, Experimental Value, Error

And now for the best part!!!! MATH!!!! ………………. . yayyy…

Calculating Error and Percent Error

Significant Figures in Measurements must always be reported to the correct number of significant figures because calculated answers often depend on the number of significant figures in the values used in the calculation. Significant Figures are measurements which include all of the digits that are known, plus a last digit that is estimated. KEYWORDS- Significant Figures

Rules for Sig Figs These rules will be used for the remainder of the course. You should make a copy and keep them on hand whenever math problems are being solved. The only time you can not use them to help you is on a test/quiz.

Rule 1 Every nonzero digit in a reported measurement is assumed to be significant. Ex: 24. 7 meters, 0. 743 meters, 714 meters All of these examples have three sig figs.

Rule 2 Zeros appearing between nonzero digits are significant. Ex: 7003 meters, 40. 79 meters, 1. 503 meters All of these measurements have 4 sig figs

Rule 3 Leftmost zeros appearing in front of nonzero digits are not significant. They act as placeholders. Ex: 0. 0071 meters, 0. 42 meters, 0. 000099 meters All of these examples have 2 sig figs To help determine sig fig amounts try writing the numbers in scientific notation.

Rule 4 Zeros at the end of a number and to the right of a decimal point are always significant. Ex: 43. 00 meters, 1. 010 meters, and 9. 000 meters All of these measurements have 4 sig figs

Rule 5 Zeros at the rightmost end of a measurement that lie to the left of an understood decimal point are not significant if they serve as placeholders to show the magnitude of the number. Ex: 300 meters, 7000 meters, 27, 210 meters The zeros in these numbers are not significant

Rule 6 Two situations involve an unlimited number of sig figs. The first is anytime something is counted, as in counting the number of people in a classroom. The second is for exactly defined quantities, such as those found within a system of measurement.

Significant Figures in Calculations In general, an answer can only be as accurate, as the least accurate measurement. This is reduced into three general areas, Sig figs in rounding, addition and subtraction, and multiplication and division.

Sig Figs in Rounding When rounding, first determine the correct number of significant figures. Then, counting from the left find the last significant figure. Next go ONE more digit to the right, if it is greater than or equal to 5, round up, if it is less than 5, drop it.

Rounding Example 4, 378. 93 What is our answer if we only need 5 sig figs? 386. 58 What is our answer if we only need 4 sig figs?

Sig Figs in Addition & Subtraction The answer to an add/sub problem should be rounded to the same number of DECIMAL places as the measurement with the least number of decimal places.

Sig Figs in Multiplication & Division In Mult/Div problems you need to round the answer to the same number of significant figures as the measurement with the least number of sig figs.

3. 2 OBJECTIVES List SI units of measurements and common SI prefixes Distinguish between the mass and weight of an object Convert between Celsius and Kelvin temperature scales. 3. 2 The International System of Units

Measuring With SI Units For this class, as well as all science classes, we use a system of measurements called the International System of Units The International System of Units (SI) is a revised version of the metric system KEYWORDS- The International System of Units

The Basic Units…

Commonly Used Metric Prefixes

Units And Quantities Length is measured in a unit known as the meter A meter is the basic SI unit of length KEYWORD-Meter

Units And Quantities A liter is used when we are discussing volume. A liter is the unit for volume used SI KEYWORD-Liter

Units And Quantities The mass of an object is measured in comparison to a standard mass of 1 kilogram (kg). A Kilogram is the basic SI unit of mass. KEYWORD- Kilogram

Mass vs Weight Mass is the amount of matter an object contains. Weight is a force that measures the pull on a given mass by gravity. KEYWORD-Weight

Units And Quantities Temperature is a measure of how hot or cold an object is and the direction of heat transfer.

The Specifics of Temperature When it comes to temperature the SI measurements vary between Celsius and Kelvin The Celsius Scale sets the freezing point of water at 0 OC and the boiling point at 100 OC KEYWORD- The Celsius Scale

The Specifics of Temperature The Kelvin Scale sets its freezing point of water at 273. 15 K, and the boiling at 373. 15 K. 0 K on the Kelvin scale is referred to as Absolute Zero KEYWORDS- The Kelvin Scale, & Absolute Zero

Units of Energy is the capacity to do work or to produce heat. The units for energy are the joule (j) and the calorie (cal). KEYWORD- Energy

3. 4 Objectives Calculate the density of a material from experimental data. Describe how density varies with temperature.

Determining Density

Density and Temperature The density of a substance generally DECREASES as its temperature INCREASES. They are inversely related.