1. Making Measurements in Chemistry

2. International System of Units A system of units based on standard units is used by scientists. The standard system used by scientists is called Le Systéme International d’Unités, abbreviated SI. In English it is called the International System of Units.

3. So that everyone in the world would have the same understanding of the units in science. What is the purpose of the International System of Units (SI Units)?

4. The SI system has seven base units that are based on an object or event in the physical world. For this test, you are responsible for knowing SI units for Time, Length, Mass and Temperature. SI Base Units QuantitySI Base Unit Symbol Time Length Mass Temperature Amount of substance Electric Current Luminous Intensity Second s Meter m kilogram kg Kelvin K Mole mol ampere A candelacd

5. This system is based on powers of ten. The prefixes we will commonly use in this system are as follows: a.kilo (k) = 1,000(1 thousand times the base unit) b.deca (da) = 10(10 times the base unit) c.deci (d) = 0.1(1/10 the base unit) d.centi (c) = 0.01(1/100 the base unit) e.milli (m)= 0.001(1/1000 the base unit) Metric prefixes to know: In addition, you should also know that: 1 cm 3 = 1 mL K = 273 + o C

6. Introduction to Dimensional Analysis In chemistry most data is in the form of a measurement. A measurement contains two parts – the number and the unit. What is the purpose of dimensional analysis? A way to analyze and solve problems using the units, or dimensions, of the measurements.

7. A "conversion factor" is a relationship between different units of measure. For example: 1 foot = 12 inches. This relationship may be written as two conversion factors: Which is used to convert inches to feet or which is used to convert feet to inches.

8. Dimensional Analysis Steps: Example 1: 57.98 mL = ___________ L ? 57.98 mL mL L 1 L = 1000 mL Is there a relationship between L and mL? 1 1000 0.05798 L

9. Example 2: 4.50 feet = _________inches ? 4.50 feet inches feet Is there a relationship between feet and inches? 12 inches = 1 foot 1 12 54.0 inches 3 sig figs

10. Example 3: 140 dimes = ___________dollars 140 dimes dimes Is there a direct relationship between dimes and dollars? 10 dimes = 1 dollar 10 dollar1 14 dollars

11. Example 4: 55 miles/ hour = ____________ km/min This problem now has units on top and bottom, so let’s take it one step at a time. 55 miles hour miles Is there a relationship between miles and kilometers? 1 km = 0.621 miles 0.621 1 km Have we arrived at the units the answer requires? NO! hour minutes Is there a relationship between hour and minutes? 1 hour = 60 minutes 1 60 1.5 km/min

12. Example 5: Pistachio nuts cost $6.00 per pound. How many pounds of nuts can be bought for $20.00? Identify the given. Identify the wanted. Is there a conversion factor given? Given wanted Conversion Factor!!! 20.00 dollar dollar pound Is there a relationship between pound and dollar? 6.00 dollar = 1 pound 6.00 1 3.333 pound

13. Example 6: How much does 4.15 lb of pistachio nuts cost? (Use given data in example 5). Identify the given. Identify the wanted. Is there a conversion factor given? Given wanted 4.15 pounds pounds dollars Is there a relationship between pound and dollar? 6.00 dollar = 1 pound 6.00 1 24.9 dollars