Mole Calculations Converting number of particles to moles Converting moles to number of particles The mole – mass relationship The mole-volume relationship

Converting Number of Particles to Moles

Converting moles to number of particles

How many atoms of sodium are in 2. 0 moles How many atoms of sodium are in 2.0 moles? Na = RP Note: Adjust answer for 1.) Scientific Notation 2.) Significant Figures

How many carbon atoms are in 3. 0 moles of C2S How many carbon atoms are in 3.0 moles of C2S? 1 molecule C2S = 1 RP 1 RP has 2 C atoms 3 mol of C2S x 2 C atoms = 6 mol C = 6 mol C x 6.0 x 1023 atoms/mol = 36 x 1023 atoms = 3.6 x 1024 atoms

Converting mole to mass Mass (grams) = number of moles x

How many grams of carbon are in 3. 0 moles of C2S. 3. 0 mol C2S = 6 How many grams of carbon are in 3.0 moles of C2S? 3.0 mol C2S = 6.0 mol C = 6.0 mol C x 12 g/mol C = 72g C

How many grams of hydrogen are in 1.5 moles of water? 1 molecule H2O = 1 RP 1 RP has 2 H atoms 1.5 mol of H2O x 2 H atom / mol = 3.0 mol H Mass = moles x atomic mass 3.0 mol H x 1.0 g/mol = 3.0 g H

What is the molar mass of 1 mol of calcium? 1 mole of any element is that compounds atomic mass expressed in grams

What is the molar mass of 1 mol of calcium? 1 mole of any element is that compounds atomic mass expressed in grams 1 mole Ca = 40.8 g / mol Because atomic mass is 40.8 amu

What is the molar mass of calcium hydroxide What is the molar mass of calcium hydroxide? Ca(OH)2 List each atom and it’s quantity. Multiply by it’s atomic mass add. Ca x 1 O x 2 H x 2 40 x 1 16 x 2 1 x 2 40 x 1 + 16 x 2 + 1 x 2 = = 74g

Converting grams to moles Grams = mass (grams) x

Calculating volume at STP Volume of gas = moles of gas x

Calculating molar mass from density Grams/mole – grams/L x 22.4 L /1 mole The density of a gaseous compound containing carbon and oxygen is found to be 1.964 g/L at STP. What is the molar mass of the compound? Molar mass = 1.964 g/L x 22.4 L/ 1 mol = 44 g/mole

Practice 1. What is the mass of 5.7 L of NH3 gas?

2. How many molecules are in 75 g of diphosphorous?

3. What is the mass of 2.5 moles of Cl2?

4. What is the volume occupied by methane, CH4 at STP?

5. How many atoms of neon gas would a container with a volume of 67 5. How many atoms of neon gas would a container with a volume of 67.2 L hold at STP?

6. Change 5.20 moles of C3H6O2 to grams.

7. Change 13.2 g of Fe(NO3)3 to moles.

8. Change 13.2 g of Sn(CO3)2 to moles.

9. How many molecules of ammonium chloride are in 54.5 g of ammonium?

10. One drop of water weighs 0. 040 g 10. One drop of water weighs 0.040 g. How many molecules are there in one drop, taking the gram formula mass (molar mass) of water to be 18 g/mol?

11. How many moles are there in 303 g of potassium nitrate 11. How many moles are there in 303 g of potassium nitrate? How many molecules are there?

12. Propane is a gas used for cooking and heating 12. Propane is a gas used for cooking and heating. How many atoms are in 2.12 mol of propane (C3H8)?

Today’s Topic Empirical Formula Molecular Formula What is the difference between empirical formula and molecular formula?

Chemical Formulas A particle composed of two or more nonmetal atoms is a molecule. A chemical formula expresses the number and types of atoms in a molecule. The chemical formula of sulfuric acid is H2SO4.

Writing Chemical Formulas The number of each type of atom in a molecule is indicated with a subscript in a chemical formula. If there is only one atom of a certain type, no ‘1’ us used. A molecule of the vitamin niacin has 6 carbon atoms, 6 hydrogen atoms, 2 nitrogen atoms, and 1 oxygen atom. What is the chemical formula? C6H6N2O

Interpreting Chemical Formulas Some chemical formulas use parenthesis to clarify atomic composition. Antifreeze has chemical formula C2H4(OH)2. There are 2 carbon atoms, 4 hydrogen atoms, and 2 OH units, giving a total of 6 hydrogen atoms and 2 oxygen atoms. Antifreeze has a total of 10 atoms.

Percent Composition The percent composition of a compound lists the mass percent of each element. For example, the percent composition of water, H2O is: 11% hydrogen and 89% oxygen All water contains 11% hydrogen and 89% oxygen by mass.

Calculating Percent Composition There are a few steps to calculating the percent composition of a compound. Lets practice using H2O. Assume you have 1 mole of the compound. One mole of H2O contains 2 mol of hydrogen and 1 mol of oxygen. 2(1.01 g H) + 1(16.00 g O) = molar mass H2O 2.02 g H + 16.00 g O = 18.02 g H2O

Calculating Percent Composition Next, find the percent composition of water by comparing the masses of hydrogen and oxygen in water to the molar mass of water: 2.02 g H 18.02 g H2O × 100% = 11.2% H 16.00 g O 18.02 g H2O × 100% = 88.79% O

Percent Composition Problem TNT (trinitrotoluene) is a white crystalline substance that explodes at 240°C. Calculate the percent composition of TNT, C7H5(NO2)3. 7(12.01 g C) + 5(1.01 g H) + 3 (14.01 g N + 32.00 g O) = g C7H5(NO2)3 84.07 g C + 5.05 g H + 42.03 g N + 96.00 g O = 227.15 g C7H5(NO2)3.

Percent Composition of TNT 84.07 g C 227.15 g TNT × 100% = 37.01% C 1.01 g H 227.15 g TNT × 100% = 2.22% H 42.03 g N 227.15 g TNT × 100% = 18.50% N 96.00 g O 227.15 g TNT × 100% = 42.26% O

Calculating the percent composition from mass data When a 13.60 g of a compound containing only magnesium and oxygen is decomposed, 5.40 g of oxygen is obtained. What is the percent composition of this compound?

Calculating composition from chemical formula Propane (C3H6) is one of the compounds obtained from petroleum. Calculate the percent composition of propane.

Empirical Formulas The empirical formula of a compound is the simplest whole number ratio of ions in a formula unit or atoms of each element in a molecule. The molecular formula of benzene is C6H6 The empirical formula of benzene is CH. The molecular formula of octane is C8H18 The empirical formula of octane is C4H9.

Empirical Formulas from Percent Composition Assume that you have 100 grams of sample. Benzene is 92.2% carbon and 7.83% hydrogen, what is the empirical formula. If we assume 100 grams of sample, we have 92.2 g carbon and 7.83 g hydrogen.

Empirical Formulas from Percent Composition Calculate the moles of each element: 1 mol C 12.01 g C 92.2 g C × = 7.68 mol C 1 mol H 1.01 g H 7.83 g H × = 7.75 mol H The ratio of elements in benzene is C7.68H7.75. Divide by the smallest number to get the formula. 7.68 C = C1.00H1.01 = CH 7.75 H

Calculating Empirical Formulas We can calculate the empirical formula of a compound from its composition data. We can determine the mole ratio of each element from the mass to determine the formula of radium oxide, Ra?O?. A 1.640 g sample of radium metal was heated to produce 1.755 g of radium oxide. What is the empirical formula? We have 1.640 g Ra and 1.755-1.640 = 0.115 g O.

A 1. 640 g sample of radium metal was heated to produce 1 A 1.640 g sample of radium metal was heated to produce 1.755 g of radium oxide. What is the empirical formula? We have 1.640 g Ra 1.755-1.640 = 0.115 g O.

Calculating Empirical Formulas The molar mass of radium is 226.03 g/mol and the molar mass of oxygen is 16.00 g/mol. 1 mol Ra 226.03 g Ra 1.640 g Ra × = 0.00726 mol Ra 1 mol O 16.00 g O 0.115 g O × = 0.00719 mol O We get Ra0.00726O0.00719. Simplify the mole ratio by dividing by the smallest number. We get Ra1.01O1.00 = RaO is the empirical formula.

Determining the empirical formula of a compound A compound is analyzed and found to contain 25.9% nitrogen and 74.1% oxygen. What is the empirical formula of the compound?

Practice Exercise Answer problems 36 and 37 on page 310.

Molecular Formulas The empirical formula for benzene is CH. This represents the ratio of C to H atoms of benzene. The actual molecular formula is some multiple of the empirical formula, (CH)n. Benzene has a molar mass of 78 g/mol. Find n to find the molecular formula. = CH (CH)n 78 g/mol 13 g/mol n = 6 and the molecular formula is C6H6.

Practice Problem Calculate the molecular formula of a compound whose molar mass is 60 g/mol and the empirical formula is CH4N.

Practice Problems Answer problems 38 and 39 on page 312 and question 45 on page 312.

Conclusions The percent composition of a substance is the mass percent of each element in that substance. The empirical formula of a substance is the simplest whole number ratio of the elements in the formula. The molecular formula is a multiple of the empirical formula.

Homework http://www.pasadena.edu/files/syllabi/cvbilicki_7032.pdf http://tw.aisj-jhb.com/jbotha/files/2013/08/Empirical-Formulas-Worksheet-1.pdf