Section 2.2 – Units of Measurement Honors Chemistry Section 2.2 – Units of Measurement

Objectives Students will be able to: Use the SI system of measurement Identify and use the prefixes Identify and use the base units Determine and use derived units Use mass and volume to calculate density Solve problems using dimensional analysis Solve dimensional analysis problems with square and cubic units.

SI Measurement Scientists all over the world have agreed on a single measurement system called Le Système International d’Unités, abbreviated SI. SI has seven base units All other units are derived from the seven base units

The unit is the standard being used to determine the measurement SI Base Units Note – the quantity is the parameter being measured.

SI Measurement

Note this uses the Base Units – we will more commonly use g/cm3 Derived SI Units The beauty of this system is all other units are “derived” by combining the seven SI Base Units in different ways. This simplifies the SI System tremendously compared to the British System Note this uses the Base Units – we will more commonly use g/cm3

Volume Volume is the amount of space occupied by an object. This is an example of a quantity. The derived SI unit is cubic meters, m3 The cubic centimeter, cm3, is more commonly used The liter, L, is a non-SI unit 1 L = 1000 cm3 1 mL = 1 cm3

Volume Video

Measuring Liquid Volume Video

Density Density is the ratio of mass to volume, or mass divided by volume. Density is a character The derived SI unit is kilograms per cubic meter, kg/m3 g/cm3 or g/mL are also used Density is a characteristic physical property (intrinsic property) of a substance.

Density Triangle Mass Density Volume

Density Density can be used as one property to help identify a substance

Conversion Factors A Conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other. example: How quarters and dollars are related

Conversion Factors Video

Conversion Factors Dimensional analysis is a mathematical technique that allows you to use units to solve problems involving measurements. example: the number of quarters in 12 dollars

Conversion Factors

Deriving Conversion Factors You can derive conversion factors if you know the relationship between the unit you have and the unit you want. example: conversion factors for meters and decimeters

Example Conversion (numbers) Example Conversion (powers of 10) Si Conversions Prefix Symbol Example Conversion (numbers) Example Conversion (powers of 10) tera T 1,000,000,000,000 m = 1 Tm 1 x 1012 m = 1 Tm giga G 1,000,000,000 m = 1 Gm 1 x 109 m = 1 Gm mega M 1,000,000 m = 1 Mm 1 x 106 m = 1 Mm kilo k 1,000 m = 1 km 1 x 103 m = 1 km hecto h 100 m = 1 hm 1 x 102 m = 1 hm deka da 10 m = 1 dam 1 x 101 m = 1 dam deci d 1 m = 10 dm 1 x 10-1 m = 1 dm centi c 1 m = 100 cm 1 x 10-2 m = 1 cm milli m 1 m = 1000 mm 1 x 10-3 m = 1 mm micro µ 1 m = 1,000,000 µm 1 x 10-6 m = 1 µm nano n 1 m = 1,000,000,000 nm 1 x 10-9 m = 1 nm pico p 1 m = 1,000,000,000,000 pm 1 x 10-12 m = 1 pm femto f 1 m = 1,000,000,000,000,000 fm 1 x 10-15 m = 1 fm atto a 1 m = 1,000,000,000,000,000,000 am 1 x 10-18 m = 1 am

Move Decimal to the Right Move Decimal to the Left Prefix Tera   Giga Mega Kilo Hecto Deka Standard Deci Centi Milli Micro Nano Pico Places 3 1 Move Decimal to the Right Move Decimal to the Left

Practice Using conversion factors, express a mass of 5.712 grams in milligrams and in kilograms.

Converting from large to small or vice versa When you are doing a complex conversion, it is always better to do it in steps that you know. If you are changing 5.86 Gm to mm, use the following logic: Gm m (the base unit) mm

Practice How many km are there in 7.88 Tm?

Conversions with Squares and Cubes Use the cube

Conversions with Squares and Cubes Use the same conversion factor. Square of cube the conversion factor as appropriate.

Practice If you have a plot of land that is 57,000 m2, how many km2 does it cover?

Practice (cont.) If you decided to use this plot of land to give each of your friends a 10 dm2 area to garden. How many friends could you invite?