Lecture 3 Units and Measurements August 20, 2010 Ozgur Unal NIS – CHEMISTRY Lecture 3 Units and Measurements August 20, 2010 Ozgur Unal

Units and Measurements The measurement of any quantity is made relative to a particular standard or unit. For centuries units of measurement were not exact. International System of Units (SI) system of units accepted in 1960. SI, is based on multiples of ten.

Base Units A base unit must be defined in terms of a standard. SI has 7 base units. All other units are derived from base units. For example: density (kg/m3), unit of speed (m/s), unit of energy (Joule)

SI BASE UNITS Measuring time: It is sometimes necessary to measure the amount of time between events (just like you did yesterday with hard and soft water samples). SI unit of time is second (s). Measuring length: Length is the distance between two points. In SI, we use meter (m) to measure distances. Measure the length of your pencil using your rulers

SI BASE UNITS Measuring matter: Mass is a measurement of the quantity of matter in an object. Unit of mass in SI is kilograms (kg) Measuring temperature: Temperature tells you how hot or cold an object is. Different units for temperature (Celsius, Kelvin, Fahrenheit). SI unit of temperature is Kelvin (K). In K scale, water freezes at 273 K and boils at 373 K. You can convert between units doing some calculations.

Derived Units Measuring volume: Volume is the amount of space occupied by an object. For objects with regular sizes (such as a brick), you can calculate the volume. Volume of a liquid is expressed in liters. 1 L = 1 dm3 Density Density is the mass per unit volume of a material. density = mass / volume Perform Minilab on page 39

NIS – CHEMISTRY Lecture 4 Scientific Notation and Unit Conversion August 23, 2010 Ozgur Unal

How old do you think the objects in the pictures are? SCIENTIFIC NOTATION How old do you think the objects in the pictures are? In science, scientific notation is used to write the numbers that are: Too big, such are the age of the universe.. Too small, such as the size of an atom

SCIENTIFIC NOTATION Scientific notation expresses any number as a number between 1 and 10 (coefficient) multiplied by 10 raised to a power (exponent) Example: Carbon atoms in the hope diamond, 4.6 x 10^23 Mass of one carbon atom, 2 x 10^-23 More examples: 700 0.0054 4,500,000 0.00000008

Operations with Scientific Notation Addition and Subtraction: In order to add or subtract numbers written in scientific notation, the exponents must be the same. (7.35x10^2 m) + (2.43x10^2 m) = 9.78x10^2 More examples in the textbook! Multiplication and Division: Two step process. 1- Multiply (divide) the coefficients for multiplication (division) 2- Add (subtract) the exponents for multiplication (division)

Operations with Scientific Notation Multiply 4.6 x 10^23 and 2 x 10^-23 1- Multiply the coefficients 4.6*2 = 9.2 2-Add the exponents 23+ (-23) = 0 The answer is 9.2 x 10^0 = 9.2 Divide 9 X 10^8 by 3 X 10^5… 1- Divide the coefficients: 9 / 3 = 3 2- Subtract the exponent in the divisor from the exponent in the dividend: 8 – 5 = 3 The answer is 3 x 10^3

Unit Conversion How do we convert 60 miles/hr to m/s? When converting one unit to another, we use conversion factors. Example: Convert 5 m to cm. Use the conversion factor 1 m = 100 cm 5m = 5 * 1 m = 5 * 100 cm = 500 cm Convert 15 miles to km: Conversion factor: 1 mile = 1.609 km 15 miles = 15 * 1 mile = 15 * 1.609 km = 24.135 km