1. Chemical Quantities The Mole

2. In this unit… You will learn how chemists count atoms by organizing large numbers of them into convenient, measurable groups. You will learn how these groups relate to the number of atoms in a substance to its mass. Using a periodic table and your calculator, you will learn how to convert between mass of a substance and the number of atoms it contains.

3. In the lab, and in the real world, it is important to be able to measure amounts accurately and conveniently. Can you imagine buying copper wire by the atom? Or paying a water bill by the molecule of water? That would be ridiculously inconvenient. On its own, the mass of a chemical is not very useful. The chemical reactions that take place depend on the number of atoms present, not the masses, but since atoms are too small and numerous to count, you need to relate the numbers to masses that can be measured.

4. Suppose you want to carry out a reaction that requires combining one atom of iron and one atom of sulfur. How much iron and sulfur would you use? There is no device that can count atoms. The smallest speck of iron contains over 4 million atoms. The same is true for sulfur? What are you going to do? Fortunately, you do have a way to relate mass to the number of atoms. It involves using relative masses from the periodic table.

5. The Mathematics of Chemistry

6. Units of Measurement Measurements represent quantities. A quantity is something that has magnitude, size, or amount. A quantity is not the same as an amount. Many centuries ago, people marked off distances in the number of foot lengths it took to cover the distance. The system was not satisfactory though, because the number of foot lengths used to express a distance varied with the size of the measurer ’ s foot. An agreed upon standard ended the confusion.

7. Le Système International d ’ Unités (SI) Scientists around the world have agreed upon a single measurement system called Le Système International d ’ Unités (SI). SI has seven base units, as well as a variety of derived units. Some non-SI units are still commonly used, such as the mile, the gallon, and the pound)

8. SI units are defined in terms of standards of measurement. The standard objects are of constant value, easy to preserve and reproduce, and are practical in size. Every measurement includes a numeral (number) and a unit. The unit has two parts: – The base unit tells you what is being measured. For example length is measured in meters. – The prefix tells you the size of the unit. For example, the prefix kilo as in kilogram, means the base unit gram is 1000 times larger.

9. The Seven Base Units

10. The Prefixes Prefixes are added to the base unit to represent quantities that are larger or smaller than the base unit.

11. The Metric System The metric system is a standard way of communicating information. It is a convention. Because it is a convention, it is important that the symbols for the units and prefixes be written as presented in the tables. A liter is L not l. The letter m by itself means meter. When written as a prefix, it means milli. Any presentation other that those given in the tables will be marked incorrect.

12. Derived Units Many units are combinations of the quantities shown in the SI Unit Table. Combinations of units are called derived units. Derived units are produced by multiplying or diving standard units.

14. Factor Label A quantity is described by a number and a unit. 125 is a number Kg is a unit 125 kg is a quantity In science we solve a lot of math by watching the units of quantities.

15. Two Main Rules in Factor Label Method 1.Always carry along the units with any measurement used. 2.Form appropriate labeled ratios (equalities)

16. Example How many centimeters in 2.35 m? Knowing that 100 cm in 1 m, set up the ratio 100 cmor1m 1m100 cm Know set up the equation 2.35 m x 100 cm = 235 cmThe conversion ratio 1mdoes not affect your sig figs

17. Rule of Thumb Starting unit = Desired Unit = Desired Unit Starting Unit

18. Practice How many wheels on 350 Ford Pickups (use the ratio of 1 pickup to 4 wheels) How many inches in 1 meter (use the ratios of 1 inch to 2.54 cm and 100 cm to 1 m) How many mm in 34 hectometers (use the ratios of 1hm to 100 m and 1m to 1000 mm)

19. If a warehouse holds 3000 boxes and a truck holds 235 boxes. How many truck loads will it take to fill up a warehouse? How many grams in 150 pounds given the ratio of 1 pound to 0.454 kg and 1 kg to 1000 g? How many weeks in 1 million seconds?