Empirical FormulasEmpirical Formulas

Percent CompositionPercent Composition

Used to describe the composition by Used to describe the composition by mass of various substances.mass of various substances.

Give individual percentage by mass Give individual percentage by mass of each element in a compound.of each element in a compound.

Percentage is alwaysPercentage is always 100Whole

Part

PracticePractice

Calculate the percent composition of Calculate the percent composition of R-22, chlorodifluoromethane, CHFR-22, chlorodifluoromethane, CHF22Cl, Cl,

the refrigerant used in home air the refrigerant used in home air conditioners.conditioners.

Empirical and Molecular FormulasEmpirical and Molecular Formulas

Consider the following compoundsConsider the following compoundsEthylene, CEthylene, C22HH44

Propylene, CPropylene, C33HH66

Cyclobutane, CCyclobutane, C44HH88

Cyclohexane, CCyclohexane, C66HH1212

All have different molecular formulasAll have different molecular formulasMolecular formulaMolecular formula – a formula telling – a formula telling

exactly how many atoms of each type are exactly how many atoms of each type are present in a moleculepresent in a molecule

Empirical and Molecular FormulasEmpirical and Molecular Formulas

Consider the following compoundsConsider the following compoundsEthylene, CEthylene, C22HH44

Propylene, CPropylene, C33HH66

Cyclobutane, CCyclobutane, C44HH88

Cyclohexane, CCyclohexane, C66HH1212

All have the same empirical formula, CHAll have the same empirical formula, CH22

Empirical formulaEmpirical formula – a formula describing – a formula describing the lowest whole number ratio of atoms in a the lowest whole number ratio of atoms in a compoundcompound

Empirical FormulasEmpirical Formulas We typically have the ability to calculate We typically have the ability to calculate

the empirical formula of a compound the empirical formula of a compound relatively easilyrelatively easily

To Determine the Empirical FormulaTo Determine the Empirical Formula

1.1. Convert the amounts of each element Convert the amounts of each element to moles.to moles.

2.2. Divide by the smallest number of Divide by the smallest number of moles to get the simplest ratio.moles to get the simplest ratio.

3.3. Adjust the ratio to get the lowest whole Adjust the ratio to get the lowest whole number ratio.number ratio.

A Simple Rhyme for a Simple A Simple Rhyme for a Simple Formula by Joel S. ThompsonFormula by Joel S. Thompson

Percent to massPercent to mass

Mass to moleMass to mole

Divide by smallDivide by small

Multiply ‘til wholeMultiply ‘til whole

PracticePracticeA 100.0g sample of a compound is found to A 100.0g sample of a compound is found to

contain 32.38g sodium, 22.65g sulfur and contain 32.38g sodium, 22.65g sulfur and 44.99g oxygen. What is the empirical 44.99g oxygen. What is the empirical formula of the compound?formula of the compound?

PracticePracticeA compound contains 26.56% potassium, A compound contains 26.56% potassium,

35.41% chromium and the remainder is 35.41% chromium and the remainder is oxygen. What is the empirical formula?oxygen. What is the empirical formula?

Adjusting the RatioAdjusting the RatioWhat do you do if you get a ratio with What do you do if you get a ratio with

something that ends in something that ends in 0.50?0.50?

Multiply by 2Multiply by 20.33 or 0.66?0.33 or 0.66?

Multiply by 3Multiply by 30.25 or 0.75?0.25 or 0.75?

Multiply by 4Multiply by 40.20, 0.40, 0.60, or 0.80?0.20, 0.40, 0.60, or 0.80?

Multiply by 5Multiply by 5

PracticePractice

Isoamyl acetate is the component of Isoamyl acetate is the component of bananas that give them their smell. It is bananas that give them their smell. It is 64.58%C, 10.84%H, 24.58% O. What is 64.58%C, 10.84%H, 24.58% O. What is the empirical formula?the empirical formula?

Empirical to Molecular FormulaEmpirical to Molecular Formula

What is the molecular formula of a compound with What is the molecular formula of a compound with an empirical formula of CHan empirical formula of CH22 and a molar mass of and a molar mass of

84.156 g/mol?84.156 g/mol? Use the ratio of the molar mass of the empirical Use the ratio of the molar mass of the empirical

formula to the molar mass of the compound.formula to the molar mass of the compound.

Empirical to Molecular FormulaEmpirical to Molecular FormulaWhat is the molecular formula for a sample What is the molecular formula for a sample

of compound that consists of 0.44g of compound that consists of 0.44g hydrogen and 6.92g oxygen? The molar hydrogen and 6.92g oxygen? The molar mass of the compound is 34.00g/mol.mass of the compound is 34.00g/mol.

PracticePracticeTheobromine, a stimulant in chocolate that is very similar Theobromine, a stimulant in chocolate that is very similar

to caffeine, has a molecular weight of 180.18g/mol, and to caffeine, has a molecular weight of 180.18g/mol, and is 46.66% C, 4.48% H, 31.10% N, and 17.76% O.is 46.66% C, 4.48% H, 31.10% N, and 17.76% O.

What is the empirical and molecular formula of this What is the empirical and molecular formula of this compound?compound?

Extra PracticeExtra PracticeLycopene, the stuff in tomatoes that contributes to Lycopene, the stuff in tomatoes that contributes to

their red color and supports prostate health in their red color and supports prostate health in men, has a molar mass of 536.90g/mol. It is men, has a molar mass of 536.90g/mol. It is 89.49%C and 10.51%H by mass.89.49%C and 10.51%H by mass.

What are the empirical and molecular formulas of What are the empirical and molecular formulas of this compound? Quintinthis compound? Quintin

HydratesHydratesA hydrate is a compound that has A hydrate is a compound that has

water loosely bound to it. The water loosely bound to it. The formula of the compound is written formula of the compound is written as:as:

formulaformula· x H· x H22OO

where x is the number of moles of where x is the number of moles of water per mole of compoundwater per mole of compound

For example, cobalt(II)chloride For example, cobalt(II)chloride hexahydrate is: hexahydrate is:

CoClCoCl22·6H·6H22OO

HydratesHydrates

Heating a hydrate causes the water to Heating a hydrate causes the water to evaporate, leaving only the evaporate, leaving only the anhydrous salt (the part of the anhydrous salt (the part of the hydrate that is not water). hydrate that is not water).

For example, if you heat For example, if you heat CoClCoCl22·6H·6H22O, the water will O, the water will

evaporate, leaving only CoClevaporate, leaving only CoCl22, ,

which is the anhydrous salt.which is the anhydrous salt.

PracticePractice

100.0g of a hydrate of copper(II) sulfate is 100.0g of a hydrate of copper(II) sulfate is heated until the water is lost and 63.93g of heated until the water is lost and 63.93g of the anhydrous salt remain. What is the the anhydrous salt remain. What is the formula of the hydrate?formula of the hydrate?

PracticePractice Ascorbic Acid, Vitamin C, is 40.92%C, Ascorbic Acid, Vitamin C, is 40.92%C,

4.58%H, and 54.50%O. It has a molar mass 4.58%H, and 54.50%O. It has a molar mass of 176.14g/mol What are the empirical and of 176.14g/mol What are the empirical and molecular formulas?molecular formulas?

PracticePractice Isoamyl acetate is the component of bananas that give Isoamyl acetate is the component of bananas that give

them their smell. It is 64.58%C, 10.84%H, 24.58% O. them their smell. It is 64.58%C, 10.84%H, 24.58% O. What is the empirical formula?What is the empirical formula?

Theobromine, a stimulant in chocolate that is very similar Theobromine, a stimulant in chocolate that is very similar to caffeine, has a molecular weight of 180.18g/mol, and to caffeine, has a molecular weight of 180.18g/mol, and is 46.66% C, 4.48% H, 31.10% N, and 17.76% O. What is 46.66% C, 4.48% H, 31.10% N, and 17.76% O. What is the empirical and molecular formula of this is the empirical and molecular formula of this compound?compound?

Lycopene, the stuff in tomatoes that contributes to their Lycopene, the stuff in tomatoes that contributes to their red color and supports prostate health in men, has a red color and supports prostate health in men, has a molar mass of 536.90g/mol. It is 89.49%C and molar mass of 536.90g/mol. It is 89.49%C and 10.51%H by mass. What are the empirical and molecular 10.51%H by mass. What are the empirical and molecular formulas of this compound?formulas of this compound?

Ascorbic Acid, Vitamin C, is 40.92%C, 4.58%H, and Ascorbic Acid, Vitamin C, is 40.92%C, 4.58%H, and 54.50%O. It has a molar mass of 176.14g/mol What are 54.50%O. It has a molar mass of 176.14g/mol What are the empirical and molecular formulas?the empirical and molecular formulas?

Test Review PracticeTest Review Practice20.0g of a hydrate of iron(III) nitrate is heated 20.0g of a hydrate of iron(III) nitrate is heated

until all the waters of hydration are lost. until all the waters of hydration are lost. 11.97g of anhydrous salt remains after 11.97g of anhydrous salt remains after heating. What is the formula of the heating. What is the formula of the compound?compound?

Glycerin is a thick liquid that is used in a wide Glycerin is a thick liquid that is used in a wide variety of situations. It is 39.12% C, 8.756% H, variety of situations. It is 39.12% C, 8.756% H, and 52.12% O and has a molar mass of about and 52.12% O and has a molar mass of about 92g/mol. What is the molecular formula of 92g/mol. What is the molecular formula of glycerin?glycerin?

Galactaric acid is a sugar acid derived from Galactaric acid is a sugar acid derived from galactose. It is 34.29% C, 4.797%H, and galactose. It is 34.29% C, 4.797%H, and 60.91% O and has a molecular weight around 60.91% O and has a molecular weight around 210amu. What is the molecular formula of 210amu. What is the molecular formula of galactaric acid?galactaric acid?