The Mole: A Measurement of MatterDescribe how Avogadros number is related to a mole of any substanceCalculate the mass of a mole of any substance

The Mole and Avogadros NumberSI unit that measures the amount of substance1 mole = 6.022 x 1023 representative particlesRepresentative particles are usually atoms, molecules, or formula units (ions)

Examples

Solve

AnswersNitrogen gas-molecule-N2Calcium fluoride-formula unit-CaF2Sucrose-molecule-C12H22O11Carbon-atom-C All have 6.022 x 1023 representative particles in 1.00 mol

How many atoms are in a mole?Determined from the chemical formulaList the elements and count the atomsSolve for CO2 C - 1 carbon atom O - 2 oxygen atoms Add: 1 + 2 = 3 Answer: 3 times Avogadros number of atoms

Solve: How many atoms are in a mole of1. Carbon monoxide CO2. Glucose C6H12O63. Propane C3H84. Water H2O

How many moles of magnesium is 1.25 x 1023 atoms of magnesium?Divide the number of atoms or molecules given in the example by 6.022 x 1023Divide (1.25 x 1023) by (6.022 x 1023)Express in scientific notationAnswer = 2.08 x 10-1 mol Mg

ObjectivesUse the molar mass to convert between mass and moles of a substanceUse the mole to convert among measurements of mass, volume, and number of particles

Molar massMass (in grams) of one mole of a substanceBroad term (can be substituted) for gram atomic mass, gram formula mass, and gram molecular massCan be unclear: What is the molar mass of oxygen? O or O2 ? - element O or molecular compound O2 ?

Molar MassGram atomic mass (gam) atomic mass of an element taken from the periodic tableGram molecular mass (gmm) mass of one mole of a molecular compoundGram formula mass (gfm) mass of one mole of an ionic compoundCan use molar mass instead of gam, gmm, or gfm

Calculating the Molar Mass of Compounds (Molecular and Ionic)1. List the elements2. Count the atoms3. Multiply the number of atoms of the element by the atomic mass of the element (atomic mass is on the periodic table)4. Add the masses of each element5. Express to hundredths place

What is the molar mass (gfm) of ammonium carbonate (NH4)2CO3?N 2 x 14.01 g = 28.02 gH 8 x 1.01 g = 8.08 gC 1 x 12.01 g = 12.01 gO 3 x 16.00 g = 48.00 gAdd ________Answer 96.11 g

Practice Problems1. How many grams are in 9.45 mol of dinitrogen trioxide (N2O3) ? a. Calculate the grams in one mole b. Multiply the grams by the number of moles2. Find the number of moles in 92.2 g of iron(III) oxide (Fe2O3). a. Calculate the grams in one mole b. Divide the given grams by the grams in one mole

Answers1. 718.39 g N2O3 (one mole is 76.02 g)2. 0.577 mol Fe2O3 (one mole is 159.70 g)

Volume of a Mole of GasVaries with a change in temperature or a change in pressureAt STP, 1 mole of any gas occupies a volume of 22.4 LStandard temperature is 0CStandard pressure is 101.3 kPa (kilopascals), or 1 atmosphere (atm)22.4 L is known as the molar volume

22.4 L of any gas at STP contains 6.022 x 1023 representative particles of that gasOne mole of a gaseous element and one mole of a gaseous compound both occupy a volume of 22.4 L at STP (Masses may differ)Molar mass (g/mol) = Density (g/L) x Molar Volume (L/mol)

ObjectivesDefine the termsCalculate the percent composition of a substance from its chemical formula or experimental dataDerive the empirical formula and the molecular formula of a compound from experimental data

Terms to KnowPercent composition relative amounts of each element in a compoundEmpirical formula lowest whole- number ratio of the atoms of an element in a compound

An 8.20 g piece of magnesium combines completely with 5.40 g of oxygen to form a compound. What is the percent composition of this compound?1. Calculate the total mass2. Divide each given by the total mass and then multiply by 100%3. Check your answer: The percentages should total 100%

AnswerThe total mass is 8.20 g + 5.40 g = 13.60 gDivide 8.2 g by 13.6 g and then multiply by 100% = 60.29412 = 60.3%Divide 5.4 g by 13.6 g and then multiply by 100% = 39.70588 = 39.7%Check your answer: 60.3% + 39.7% = 100%

Calculate the percent composition of propane (C3H8)1. List the elements2. Count the atoms3. Multiply the number of atoms of the element by the atomic mass of the element (atomic mass is on the periodic table)4. Express each element as a percentage of the total molar mass5. Check your answer

AnswerTotal molar mass = 44.11 g/mol36.03 g C = 81.68% 8.08 g H = 18.32%

Calculate the mass of carbon in 82.0 g of propane (C3H8)1. Calculate the percent composition using the formula (See previous problem)2. Determine 81.68% of 82.0 g Move decimal two places to the left (.8168 x 82 g)3. Answer = 66.98 g

Calculating Empirical FormulasMicroscopic atomsMacroscopic moles of atomsLowest whole-number ratio may not be the same as the compound formula Example: The empirical formula of hydrogen peroxide (H2O2) is HO

Empirical FormulasThe first step is to find the mole-to-mole ratio of the elements in the compoundIf the numbers are both whole numbers, these will be the subscripts of the elements in the formulaIf the whole numbers are identical, substitute the number 1 Example: C2H2 and C8H8 have an empirical formula of CHIf either or both numbers are not whole numbers, numbers in the ratio must be multiplied by the same number to yield whole number subscripts

What is the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen?1. Assume 100 g of the compound, so that there are 25.9 g N and 74.1 g O2. Convert to mole-to-mole ratio: Divide each by mass of one mole 25.9 g divided by 14.01 g = 1.85 mol N 74.1 g divided by 16.00 g = 4.63 mol O3. Divide both molar quantities by the smaller number of moles

4. 1.85/1.85 = 1 mol N 4.63/1.85 = 2.5 mol O5. Multiply by a number that converts each to a whole number (In this case, the number is 2 because 2 x 2.5 = 5, which is the smallest whole number )2 x 1 mol N = 22 x 2.5 mol O = 5Answer: The empirical formula is N2O5

Determine the Empirical Formulas1. H2O2 2. CO2 3. N2H44. C6H12O65. What is the empirical formula of a compound that is 3.7% H, 44.4% C, and 51.9% N?

AnswersCompound Empirical Formula1. H2O2 HO2. CO2 CO2 3. N2H4 NH24. C6H12O6 CH2O

5. HCN

Calculating Molecular FormulasThe molar mass of a compound is a simple whole-number multiple of the molar mass of the empirical formulaThe molecular formula may or may not be the same as the empirical formula

Calculate the molecular formula of the compound whose molar mass is 60.12 g and empirical formula is CH4N.1. Using the empirical formula, calculate the empirical formula mass (efm) (Use the same procedure used to calculate molar mass.)2. Divide the known molar mass by the efm 3. Multiply the formula subscripts by this value to get the molecular formula

AnswerMolar mass (efm) is 30.06 g60.12 g divided by 30.06 g = 2Answer: C2H8N2