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Mole Calculations Converting number of particles to moles
Converting moles to number of particles The mole – mass relationship The mole-volume relationship
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Converting Number of Particles to Moles
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Converting moles to number of particles
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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
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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
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Converting mole to mass
Mass (grams) = number of moles x
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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
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How many grams of hydrogen are in 1.5 moles of water?
1 molecule H2O = 1 RP 1 RP has 2 H atoms 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
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What is the molar mass of 1 mol of calcium?
1 mole of any element is that compounds atomic mass expressed in grams
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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
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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 x x x x x x 2 = = 74g
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Converting grams to moles
Grams = mass (grams) x
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Calculating volume at STP
Volume of gas = moles of gas x
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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 g/L at STP. What is the molar mass of the compound? Molar mass = g/L x L/ 1 mol = 44 g/mole
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Practice 1. What is the mass of 5.7 L of NH3 gas?
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2. How many molecules are in 75 g of diphosphorous?
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3. What is the mass of 2.5 moles of Cl2?
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4. What is the volume occupied by methane, CH4 at STP?
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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?
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6. Change 5.20 moles of C3H6O2 to grams.
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7. Change 13.2 g of Fe(NO3)3 to moles.
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8. Change 13.2 g of Sn(CO3)2 to moles.
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9. How many molecules of ammonium chloride are in 54.5 g of ammonium?
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10. One drop of water weighs 0. 040 g
10. One drop of water weighs g. How many molecules are there in one drop, taking the gram formula mass (molar mass) of water to be 18 g/mol?
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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?
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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)?
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Today’s Topic Empirical Formula Molecular Formula
What is the difference between empirical formula and molecular formula?
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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.
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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
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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.
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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.
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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 g O = g H2O
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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
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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 g O) = g C7H5(NO2)3 84.07 g C g H g N g O = g C7H5(NO2)3.
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Percent Composition of TNT
84.07 g C g TNT × 100% = 37.01% C 1.01 g H g TNT × 100% = 2.22% H 42.03 g N g TNT × 100% = 18.50% N 96.00 g O g TNT × 100% = 42.26% O
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Calculating the percent composition from mass data
When a 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?
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Calculating composition from chemical formula
Propane (C3H6) is one of the compounds obtained from petroleum. Calculate the percent composition of propane.
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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.
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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 g carbon and 7.83 g hydrogen.
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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
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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 g sample of radium metal was heated to produce g of radium oxide. What is the empirical formula? We have g Ra and = g O.
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A 1. 640 g sample of radium metal was heated to produce 1
A g sample of radium metal was heated to produce g of radium oxide. What is the empirical formula? We have 1.640 g Ra = g O.
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Calculating Empirical Formulas
The molar mass of radium is g/mol and the molar mass of oxygen is g/mol. 1 mol Ra g Ra 1.640 g Ra × = mol Ra 1 mol O 16.00 g O 0.115 g O × = mol O We get Ra O Simplify the mole ratio by dividing by the smallest number. We get Ra1.01O1.00 = RaO is the empirical formula.
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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?
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Practice Exercise Answer problems 36 and 37 on page 310.
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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.
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Practice Problem Calculate the molecular formula of a compound whose molar mass is 60 g/mol and the empirical formula is CH4N.
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Practice Problems Answer problems 38 and 39 on page 312 and question 45 on page 312.
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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.
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Homework http://www.pasadena.edu/files/syllabi/cvbilicki_7032.pdf
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