UNIT II.1 Unit Conversions

II.1 UNIT CONVERSIONS In chemistry, we will be converting from one unit to the other all the time… You MUST learn and use the unit conversion method (not your own method) it will make your life easy! A CONVERSION FACTOR: is a fractional expression relating or connecting two different units.

II.1 UNIT CONVERSIONS Example 1: There are 60 seconds in 1 minute. This is a statement form. We can also write it as: The conversion factor relates 2 units (ex; minutes to seconds).

II.1 UNIT CONVERSIONS Example 2: $1.44 per dozen eggs. Conversion Factors: Conversion factors do not change the VALUE of something, ever…. We simply use them to change from one unit to another!

II. 1 UNIT CONVERSIONS THE UNIT CONVERSION METHOD We need 3 important pieces of information: Desired amount and units ( what we want ) Initial amount and units ( what we know/already have ) Conversion factor (relating the initial units to units of unknown)

II. 1 UNIT CONVERSIONS Example 3: How many seconds are in 20 minutes?

II.1 UNIT CONVERSIONS Example 4: If a car can go 90km in 1 h, how far can the car go in 6.5 h?

II.1 UNIT CONVERSIONS Example 5: If the price of gas is $1.10 per liter (l), how much will it cost to fill a 40 liter tank?

II.1 UNIT CONVERSIONS HOW TO PUT EVERYTHING TOGETHER The general form of a unit conversion calculation is: (wanted amount) = ( Initial amount) x (Conversion factor)

II.1 UNIT CONVERSIONS Example 6 a. If mL of gold has a mass of 3.86 g, what is the mass of 5.00 mL of gold?

II.1 UNIT CONVERSIONS *Important: Always ask yourself “which way do I have to write the conversion factor so that my units cancel properly?” b. If mL of gold has a mass of 3.86 g, what is the volume occupied by g of gold?

II.1 UNIT CONVERSIONS SUMMARY Identify wanted/desired amount and its units (put on left side of = sign). Identify the initial amount and its units (put on right side of = sign). 3. Identify conversion factor. (Multiply initial amount by conversion factor in such a way that one of the units cancels. You want to be left with units of wanted amount!) 4. Complete the problem by multiplying and/or dividing

p 14. Exercise 2 d) How many seconds must an electrical current of 35 coulombs/s flow in order to deliver 200 coulombs?

Practice Questions: Hebden, p 11 Exercise 1. a, c, e, g, i p 14. Exercise 2. b, f, h, j

Multiple CONVERSIONS The automobile gas tank of a Canadian tourist holds 39.5 l of gas. If 1 L of gas is equal to gal in the USA (“gal” is the symbol for “gallon”, a measure of volume used in the US), and gas is $1.26/gal in Dallas, Texas, how much will it cost the tourist to fill his gas tank in Dallas?

Exercise 4, page 15

Practice time Hebden, p 15 Exercises 3 – 10 except 4