Stoichiometry Greek Translation –Stoicheion – means “element” –Metron – means “measure” Element Measuring

Stoichiometry EQ: How do we compare elements so that we can measure them? For example, does… 23 grams of Na = 23 grams of Cl 23g Na x 1 mol = 1 mol Na or 6.022E 23 atoms 23g 23g Cl x 1mol = 0.65 mol Cl or 3.85E 23 atoms 35.5g

Stoichiometry So how much Chlorine do I need since NaCl is a one to one ratio? 23g Na x 1 mol = 1 mol Na or 6.022E 23 atoms 23g 35.5g Cl x 1mol = 1 mol Cl or 6.022E 23 atoms 35.5g 23g Na = 35.5g Cl

Stoichiometry What if all I had was 23 grams of Chlorine? How much NaCl could l make? 23g Na x 1 mol = 1 mol Na or 6.022E 23 atoms 23g 23g Cl x 1mol = 0.65 mol Cl or 3.85E 23 atoms 35.5g Limiting Reagent

Chemical Stoichiometry Stoichiometry - The study of quantities of materials consumed and produced in chemical reactions. Mole  Mole Mass  Mole Mole  Mass Mass  Mass Consumed  Produced

Review: The Mole  The number equal to the number of carbon atoms in exactly 12 grams of pure 12 C.  1 mole of anything = ´ units of that thing

Review: Molar Mass A substance’s molar mass (molecular weight) is the mass in grams of one mole of the compound. CO 2 = grams per mole H 2 O = grams per mole Ca(OH) 2 = grams per mole

Review: Chemical Equations Chemical change involves a reorganization of the atoms in one or more substances. C 2 H 5 OH + 3O 2  2CO 2 + 3H 2 O reactantsproducts 1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and 3 moles of water When the equation is balanced it has quantitative significance:

Mole to Mole Problems Ammonia, NH 3, is widely used as fertilizer and in many household cleaners. How many moles of ammonia are produced when 6 mol of hydrogen gas react with an excess of nitrogen gas? N 2 + H 2  NH 3 2=N=1 2=H= mol H 2(g) mol unknown mol known X 2 mol NH 3 = 4 mol NH 3 3 mol H 2 Step 1: Step 2: Step 3: Step 4 :

Mole to Mole Problems The decomposition of potassium chlorate, KClO 3, is used as a source of oxygen in the laboratory. How many moles of potassium chlorate are needed to produce 15 mol of oxygen?

Mole to Mass Problems In photosynthesis, plants use energy from the sun to produce glucose, C 6 H 12 O 6, and oxygen from the reaction of carbon dioxide and water. What mass, in grams, of glucose is produced when 3.00 mol of water react with carbon dioxide? 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O mol H 2 O X 1 mol C 6 H 12 O 6 X 6 mol H 2 O g = 1 mol C 6 X = H 12 X 1.01 = O 6 X = g/mol 90.09g C 6 H 12 O 6

Mole-Mass Problem Solution of iron (III) chloride, FeCl 3, are used in photoengraving and to make ink. This compound can be made by the following reaction. 2 Fe + 3 Cl > 2 FeCl 3 How many grams of FeCl 3 form from 2.4 moles of Fe?

Mass to Mole Problems The first step in the industrial manufacture of nitric acid is the catalytic oxidation of ammonia. NH 3 + O2 O2  NO + H 2 O (unbalanced) The reaction is run using 824 g of NH 3 and excess oxygen. a.How many moles of NO are formed? b.How many moles of H 2 O are formed? A. 824g NH 3 X 1 mol X 4 mol NO = mol NO 17.03g NH 3 4 mol NH 3 N X = H 3 X 1.01 = g/mol B. 824g NH 3 X 1 mol X 6 mol H 2 O = mol H 2 O 17.03g NH 3 4 mol NH 3

Mass to Mole Problems Oxygen was discovered by Joseph Priestley in 1774 when he heated mercury (II) oxide to decompose it to form its constituent elements. a.How many moles of mercury (II) oxide are needed to produce 125 g of oxygen? b.How many moles of mercury are produced?

Mass to Mass Problems When copper metal is added to silver nitrate in solution, silver metal and copper (II) nitrate are produced. What mass of silver is produced from 100. g of Cu? Cu + Ag(NO 3 )  Ag + Cu(NO 3 ) g Cu X 1 mol Cu X 2 mol Ag X g = g Ag 63.55g 1 mol Cu 1 mol Ag Molar Mass

Mass to Mass Problems Tin (II) fluoride is used in some toothpastes. It is made by the reaction of tin (II) with hydrogen fluoride according to the following equation. Sn + 2 HF  SnF 2 + H 2 How many grams of SnF 2 are produced from the reaction of g of HF with Sn?

Mole-Mole How many moles of carbon dioxide, CO 2, can be made from Fe 2 O 3 by the use of 1.90 moles of carbon monoxide, CO, in the following reaction? Fe 2 O CO > 2 Fe + 3 CO 2

Mole- Mass Problem The Solvay process is used to make sodium carbonate, Na 2 CO 3, a chemical that ranked 11th among all chemicals in annual production in The process begins with the passing of ammonia and carbon dioxide through a solution of sodium chloride. This makes sodium bicarbonate and ammonium chloride: H 2 O + NaCl + NH 3 + CO > NH 4 Cl + NaHCO 3 The Solvay process is used to make sodium carbonate, Na 2 CO 3, a chemical that ranked 11th among all chemicals in annual production in The process begins with the passing of ammonia and carbon dioxide through a solution of sodium chloride. This makes sodium bicarbonate and ammonium chloride: H 2 O + NaCl + NH 3 + CO > NH 4 Cl + NaHCO 3 How many grams of sodium bicarbonate could, in theory, be How many grams of sodium bicarbonate could, in theory, be made from 5 moles of ammonia, NH 3 ? made from 5 moles of ammonia, NH 3 ?

Mass-Mole Using the equation: Pb(SO 4 ) LiNO 3  Pb(NO 3 ) Li 2 SO 4, How many moles of lithium nitrate will be needed to make 250 grams of lithium sulfate, assuming that you have an adequate amount of lead (IV) sulfate to do the reaction?

Mass to Mass Problems What mass of aluminum is produced by the decomposition of 5.0 kg of Al 2 O 3 ?

Mole to Mole Problems CO LiOH  Li 2 CO 3 + H 2 O Given:20 mol CO 2 Unknown:X mol LiOH 20 molX mol 20 mol CO 2 ×= mol LiOH The MOLE TRAIN!!!!!! Mole Train How can we go from moles of one compound to mole of another compound? Use the mole ratio, Duh! 2 mol LiOH 1 mol CO 2 40 How many moles of lithium hydroxide are required to react with 20 moles of carbon dioxide?

How many moles of water are produced in the complete combustion of 1.00 moles of glucose according to the following reaction: C 6 H 12 O 6 + 6O > 6CO 2 + 6H 2 O 6 mole H 2 O 1.00 moles C 6 H 12 O 6 X moles C 6 H 12 O moles of water

What mass of H 2 SO 4 can be formed from 5.0 moles of SO 2 and an unlimited quantity of H 2 O and O 2 ? 2SO 2 + O 2 + 2H 2 O ----  2H 2 SO 4 2 moles H 2 SO 4 98 grams H 2 SO moles SO2 X X moles SO2 1 mole H 2 SO grams

The newly discovered element Takalahium (symbol Tak; molecular mass = 411 g/mol) combines with oxygen to form Takalahium Oxide. The unbalanced equation is: Tak + O 2 ---> Tak 2 O 3 How many grams of Tak Oxide are formed when burning 8.00 moles of Tak? 2 mole Tak 2 O grams Tak 2 O moles Tak X X mole Tak 1 mole Tak 2 O grams

A piece of zinc metal weighing 2.00 grams is placed in an aqueous solution of silver nitrate. How many moles of silver can be recovered from this single replacement reaction? 1 Zn + 2 AgNO 3  1 Zn(NO 3 ) Ag 1 mole Zn 2 moles Ag 2.00 grams Zn X X grams Zn 1 mole Zn.061 moles

Mass- Mole Problem The octane present in gasoline burns according to the following equation: 2 C 8 H O2 O > 16 CO H2OH2O How many moles of CO 2 are produced when 30 grams of octane react with an excess of oxygen? 1 mole C 8 H moles CO 2 30 grams C 8 H 18 X X grams C 8 H 18 2 mole C 8 H moles

The formation of water from hydrogen and oxygen gas is: 2H 2 (g) + O2 O2 ---> 2H 2 O (l). What mass of water will form from 12.0 grams of hydrogen and excess oxygen? 1 mole H 2 2 mole H 2 O 18 grams H 2 O 12.0 grams H 2 X X X grams H 2 2 moles H 2 1 mole H 2 O 108 grams

In the reaction: KClO 3 + 5KCl + 6HNO 3 --> 6KNO 3 + 3Cl 2 + 3H 2 O, how many grams of KClO 3 are required to prepare 10.0 g of Cl 2 ? 1 mole Cl 2 1 mole KClO grams KClO 3 10 grams Cl 2 X X X grams Cl 2 3 moles Cl 2 1 mole KClO grams

Working a Stoichiometry Problem 6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed? 4 Al + 3 O 2  2Al 2 O 3 = 6.50 g Al ? g Al 2 O 3 1 mol Al g Al 4 mol Al 2 mol Al 2 O 3 1 mol Al 2 O g Al 2 O x 2 x ÷ ÷ 4 =12.3 g Al 2 O 3

LLLL iiii mmmm iiii tttt iiii nnnn gggg R R R R eeee aaaa cccc tttt aaaa nnnn tttt Video The limiting reactant is the reactant that is consumed first, limiting the amounts of products formed. The limiting reactant is the reactant that is consumed first, limiting the amounts of products formed.

Analogy You need to bake some cakes for the school bake sale. The cake recipe calls for 2 cups of flour and 4 eggs. If you have 4 cups of flour and a dozen of eggs, how many cakes can you make? 2 cups flour 4 eggs 4 cups of flour X = 2 cakes 2 cups flour = 1 cake 4 eggs Which ingredient ran out first (limiting)?

Silicon dioxide is usually quite unreactive but reacts readily with hydrogen fluoride according to the following equation. SiO HF  SiF H2OH2O If 2.0 mol of HF are exposed to 4.5 mol of SiO 2, which is the limiting reactant? 4.5 mol SiO mol HF 1 mol SiO 2 4 mol HF Look at the balanced equation and mole-to-mole ratio

If 12.0 g CH 4 and 24.0 g O 2 react to form CO 2 and H 2 O, how many grams of CO 2 will be formed? 1 CH O 2  1 CO H 2 O 1 mole CH 4 2 mole O 2 32 grams O 2 12 grams CH 4 X X X grams CH 4 1 mole CH 4 1 mole O 2 Need: 48 grams- O 2 Limited: O 2 will run out first 1 mole O 2 1 mole CO 2 44 grams CO 2 24 grams O 2 X X X grams O 2 2 moles O 2 1 mole CO grams CO 2 How do you know which one to use?

Practice Methane (CH 4 ) reacts with O 2 to form CO 2 and water. If 30.0 grams of CH 4 and 64.0 grams of O 2 are mixed and the reaction goes to completion, how many grams of the reactant "in excess" remain? 1 CH O 2  1 CO H 2 O 1 mole O 2 1 mole CH 4 16 grams CH 4 64 grams O 2 X X X grams O 2 2 mole O 2 1 mole CH 4 Will Use 16 grams CH 4 Excess Remaining = 30.0 grams – 16 grams = 14 grams

Some rocket engines use a mixture of hydrazine, N 2 H 4, and hydrogen peroxide, H 2 O 2, as the propellant. The reaction is given by the following equation. N 2 H H 2 O 2  N H 2 O a. Which is the limiting reactant in this reaction when mol of N 2 H 4 is mixed with mol of H 2 O 2 ? b. How much of the excess reactant, in moles, remains unchanged? c. How much of each product, in moles, is formed?

The black oxide of iron, Fe 3 O 4, occurs in nature as the mineral magnetite. This substance can also be made in the laboratory by the reaction between red-hot iron and steam according to the following equation. 3 Fe + 4 H 2 O  Fe 3 O H 2 a.When 36.0 g of H 2 O is mixed with 167 g of Fe, which is the limiting reactant? b. What mass in grams of black iron oxide is produced? c. What mass in grams of excess reactant remains when the reaction is completed?

In the reaction PCl 5 --> PCl 3 + Cl 2, g of PCl 5 are used, and 30.0 g of Cl 2 are produced. What is the % yield of Cl 2 in this reaction? % Yield = Actual Yield (given in problem) X 100 Theoretical Yield (find with stoichiometry) grams PCl 5 X 1 mole PCl 5 X 1 mole Cl 2 X 70.9 grams Cl grams PCl 5 1 mole PCl 5 1 mole Cl 2 Theoretical Yield= 35.5 grams Actual Yield = 30.0 grams Percent Yield = 30.0 grams Cl 2 X grams Cl 2 Ans: 84.5 % Ans: 35.5

How many grams of CaF 2 is formed when 35.8mL of M NaF is treated with excess of Ca(NO 3 ) 2 (aq)? M = mL X __1 L_ X mol X 1 mol CaF 2 X 78g CaF mL 1L 2 mol NaF 1 mol NaF + Ca(NO 3 ) 2  CaF 2 + Na 2 (NO 3 ) g CaF 2

Determine which compound is limiting The reaction needs 14.4g of AgNO 3 But we only have 6.00g. The reaction will stop when AgNO 3 is gone Now that you know which is the limiting reagent we can use it’s mass to solve for how many grams of Ag2CO 3

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