Chapter 2 Analyzing Data CHEMISTRY Chapter 2 Analyzing Data

Section 2.1 Units and Measurements In Chemistry, we use the SI for our measurements and calculations. There are 7 Base Units in the SI. A base unit is a defined unit in a system of measurement that is based on an object or event in the physical world, and is independent of other units.

SI Base Units

Kangaroos Have Died Drinking Chocolate Milk!!!!!!!!!!!!!!!!!! Kilo Hecto Deka 1 Deci Centi Milli 103 102 101 10-1 10-2 10-3 Mega 106 Micro 10-6

The SI base unit of time is the second (s), based on the frequency of radiation given off by a cesium-133 atom. The SI base unit for length is the meter (m), the distance light travels in a vacuum in 1/299,792,458th of a second. The SI base unit of mass is the kilogram (kg), about 2.2 pounds.

The SI base unit of temperature is the kelvin (K). Zero kelvin is the point where there is virtually no particle motion or kinetic energy, also known as absolute zero. Two other temperature scales are Celsius and Fahrenheit. K = 0C + 273

Not all quantities can be measured with SI base units!!! A unit that is defined by a combination of base units is called a derived unit. Can you think of any examples?????

Volume is measured in cubic meters (m3), but this is very large Volume is measured in cubic meters (m3), but this is very large. A more convenient measure is the liter, or one cubic decimeter (dm3).

Density is a derived unit, g/cm3, the amount of mass per unit volume. The density equation is density = mass/volume D = M / V

Section 2.2 Scientific Notation and Dimensional Analysis Scientific notation can be used to express any number as a number between 1 and 10 (the coefficient) multiplied by 10 raised to a power (the exponent). To write a number in scientific notation, count the number of places the decimal point must be moved to give a coefficient between 1 and 10. The number of places moved equals the value of the exponent. If the original number is >1, it will have a positive exponent or it will have a negative exponent if the original number was <1.

Time to practice… Proton Mass: 0.000000000000000000000000001673 kg Sun Temperature: 15 000 000 K HIV Length: 0.00000011 m Mass of Moon: 73 490 000 000 000 000 000 000 kg

Dimensional analysis is a systematic approach to problem solving that uses conversion factors to move, or convert, from one unit to another. A conversion factor is a ratio of equivalent values having different units. Given unit   desired unit desired unit given unit Conversion factor

Section 2.3 Uncertainty in Data Accuracy refers to how close a measured value is to an accepted value. Precision refers to how close a series of measurements are to one another.

What would we always like for our % Error to equal??? Percent error expresses error as a percentage of the accepted value. % Error = │exp – acc │ (100) acc What would we always like for our % Error to equal???

Different measuring devices have different uses and different degrees of accuracy.

Significant figures include all known digits plus one estimated digit.

Pacific - Atlantic Rule for Significant Digits If the decimal is present, start on the Pacific side (left) at the first nonzero digit and count it and all the digits to the right of it. 2.If the decimal is absent, start on the Atlantic side (right) at the first nonzero digit and count it and all the digits to the left of it.

Addition and subtraction - Round numbers so the final answer has the same number of decimal places as the measurement with the least number of decimal places. Multiplication and Division - Round the final answer so that it has as many significant figures as the least number of significant figures.