Ch. 6 Chemical Quantities

1. Ch. 6 � Chemical Quantities The Mole What is a mole? It is a unit for _________in chemistry. It is similar to a dozen, except instead of 12 things, it�s 602 billion trillion things� (602,000,000,000,000,000,000,000) ___________ (in scientific notation) This number is named in honor of Amedeo _________ (1776 � 1856), who studied quantities of gases and discovered that equal volumes of gases under the same conditions of temperature and pressure contained the same number of particles.

3. Just How Big is a Mole? It�s enough soft drink cans to cover the surface of the earth to a depth of over 200 miles. If you had Avogadro's number of un-popped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles. If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

4. 1 dozen cookies = ___ cookies 1 mole of cookies = ___________ cookies 1 dozen cars = ___ cars 1 mole of cars = __________ cars 1 dozen Al atoms = ___ Al atoms 1 mole of Al atoms = __________ atoms Mole is abbreviated ______ . The Mole

6. 3) Convert 835 grams of SO3 to moles. 4) How many molecules of CH4 are there in 18 moles? 5) How many grams of helium are there in 5.6 x 1023 atoms of helium? 6) How many molecules are there in 3.7 grams of H2O?

7. Calculating Percent Composition by Mass Step 1: Find the molar mass of the compound by adding the individual masses of the elements together. Step 2: Divide each of the individual masses of the elements by the molar mass of the compound. Step 3: Convert the decimal to a % by multiplying by 100. Practice Problems: (1) Find the % composition of the elements in each compound. a) Na3PO4 b) SnCl4

8. Elements in the Universe: % Composition by Mass

9. Earth�s Crust: % Composition by Mass

10. Entire Earth (Including Atmosphere):  % Composition by Mass

11. Human Body: % Composition by Mass

12. Determining the Empirical Formula for a Compound The empirical formula for a compound is the simplest __________ number __________ of the atoms in the compound. Examples: H2O is the empirical formula for water. _______ is the empirical formula for glucose, C6H12O6. Step 1: Divide the % composition data by the atomic mass of the element. This will give you a ratio of the # of atoms in the formula. Step 2: Divide each of these answers by the smallest ratio. Step 3: If there is still a decimal, multiply each answer by the denominator of the �freak�, (i.e. -- multiply all the ratios by the denominator of the ratio that is still a decimal.) [1/2= 0.5 1/3� 0.33 2/3� 0.67 3/4= 0.75]

15. Determining the Molecular Formula for a Compound The molecular formula for a compound is either the same as the empirical formula ratio or it is a �_________ _________ of this ratio. It represents the true # of atoms in the molecule. Examples: 1) H2O is the empirical & molecular formula for water. 2) CH2O is the empirical formula for sugar, ethanoic acid, and methanol. The molecular formula for glucose is C6H12O6, (___times the empirical ratio!) Step 1: Determine the empirical formula for the compound. (See the previous steps in the notes.) Step 2: Calculate the empirical formula mass of the compound. Step 3: Determine the �whole # multiple� by dividing the molecular formula mass (given in the problem) by the empirical formula mass. Multiply each of the empirical ratios by this whole number.