THE MOLE Chapter 10: Chemical Quantities

10.1 Measuring Matter What is a mole? It is the SI unit that measures the amount of substance.

Mole Mass s Volume Number of Particles

 Avogadro’s number  Simply multiply by 6.02 x 10 23

 How many moles of magnesium is 1.25 x atoms of magnesium?  How many atoms are in 2.12 mol of propane? (C 3 H 8 )

 Multiply by the molecular mass of the substance.  Molar mass: mass (in grams) of one mole of the substance

 How many grams are in 9.45 mol of dinitrogen trioxide (N 2 O 3 )?  How many moles in 92.2 g of iron (III) oxide (Fe 2 O 3 )?

 The Special Number 22.4

 volume varies with changes in temperature and pressure › usually measured at STP (0 o C; kPa) › at STP, one mole of any gas occupies a volume of 22.4 L

 Determine the volume, in liters, of 0.60 mol SO 2 gas at STP.  The density of a gaseous compound containing carbon and oxygen is g/L at STP. Determine the molar mass of the compound.

 Mass / molecular mass  Volume / 22.4  Number of particles / Avogadro’s number

 Percent by mass of each element in a compound  % mass of element = Grams of element X Grams of compound X 100

 9.03 g Mg combine completely with 3.48 g N to form a compound. What is the % composition of this compound?  Calculate the % composition of ethane (C 2 H 6 ).

 Calculate the mass of hydrogen in 350 g C 3 H 8.

 Lowest whole number ratio of atoms of an element in a compound. › May or may not be the same as the molecular formula!

 Give the empirical formula for a compound which is 25.9% Nitrogen and 74.1% Oxygen.  Assume it is a 100g sample, so 25.9g N and 74.1g of O  25.9/14 =1.85 moles of N 74.1/16 = 4.63 moles of O 1.85/1.85 = 14.63/1.85 = 2.5 Double both numbers to get a whole number ratio… N 2 O 5

 Calculate the empirical formula of a compound that is 79.8% C and 20.2% H.  Calculate the molecular formula of a compound whose molecular mass is 62 g/mol and empirical formula is CH 3 O.

 Compounds with specific numbers of water molecules bound to their atoms are called hydrates.  In the formula, a dot is used to show that water is bonded. Use a prefix to name the hydrate. › Na 2 CO 3 ∙ 10H 2 O Sodium carbonate decahydrate

 In order to analyze a hydrate, you must first find the number of moles of water associated with one mole of the hydrate. › Heat the sample to drive off the water, then you can mass the anhydrous compound and determine the moles of water.

 An 11.75g sample of a common hydrate of cobalt (II) chloride is heated. After heating, mol of anhydrous cobalt chloride remains. What is the formula and the name of this hydrate?

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