Chemistry Section 2 1 Multiple Conversions Multiple Unit

Chemistry Section 2. 1 Multiple Conversions

Multiple Unit conversions • Set up conversion factors so the units cross out. The only difference now is that you will have more than one conversion factor. Unknown Amount Initial Amount Conversion FACTORS

• • • Steps: Units you are converting to. Initial unit. Figure out the conversion factors. Do the math

Example • To melt 1 kg of ice, 334 k. J of heat is required. The largest known iceberg had a volume of about 3. 1 x 1013 m 3. How much heat was required to melt the iceberg if 1 m 3 of ice has a mass of 917 kg?

• • Looking for Number of k. J Initial: 3. 1 x 1013 m 3 Conversion: 1 m 3 = 917 kg, 334 k. J/1 kg Amount of heat = 3. 1 x 1013 m 3 X 917 kg/ 1 m 3 X 334 k. J/1 kg = 9. 5 X 1018 k

• • • How many grams are there in 5 kilograms. 1) Unknown: g 2) Initial: 5 kg. 3) Conversion Factor: 1 kg = 1000 g 4) # g = (5 kg) *(1000 g/1 kg) = 5 X 103 g

• Multiple conversion example • You always want to go from initial unit to base unit (g, m, L, mol and so on) before unknown unit. • You will have two conversion statements. One to convert to the base unit and another to convert to the new unit.

Express 6 m. L in k. L. 1) k. L 2) 6 m. L 3) 1 m. L = 10 -6 L and 1 k. L = 103 L 5) unknown # k. L = (6 m. L) * (10 -6 L/ 1 m. L) * (1 k. L/ 103 L)=6 X 10 -9 k. L - Remember, you are playing with units. Learn how to cross out units and you have it made. • -

Unit conversions containing two units, ie. g/m. L (Density). • • • Express 6 g/L into kg/m. L 1) kg/m. L 2) 6 g/L 3) 1 kg = 1000 g, 1 m. L = 10 -3 L You want to convert the top from g to kg and bottom form m. L to L. • Convert the top and then the bottom, applying the conversion factors one after each other. • # kg/m. L = 6 g/L * 1 kg/1000 g * 10 -3 L/1 m. L = 6 x 10^-6 kg/m. L • Notice how the units cross out and you are left out with the unknown units.

• • Questions 3, 5, 7, 9. (Page 15 – 16) 17 a – j. (Page 21) 24, 25, 28. (Page 22) Quiz on unit conversions next day.