Consider the reaction of Fe in the air: Consider the reaction of Fe in the air


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Consider the reaction of Fe in the air:

  • Consider the reaction of Fe in the air:

  • 4Fe + 3O2  2Fe2O3

  • Balanced Equations (kinda like a recipe!)

  • MOLE RATIOS!!!

  • What is the mole ratio of Fe to O2?

  • 4 mole Fe

  • 3 mole O2



Stoichiometry

  • Stoichiometry

  • a problem solving method using dimensional analysis and MOLAR RATIOS!!!



The 4-step rule is an aid to guide you through the D.A. of Stoich!!!

  • The 4-step rule is an aid to guide you through the D.A. of Stoich!!!

  • This might just be your new best friend.



Ex 1: how many moles of KClO3(s), must decompose in order to produce 9.0 moles of oxygen gas? The other product is potassium chloride.

  • Ex 1: how many moles of KClO3(s), must decompose in order to produce 9.0 moles of oxygen gas? The other product is potassium chloride.



Write the balanced equation for the reaction and use it as a data table

  • Write the balanced equation for the reaction and use it as a data table



Find moles of the “given” using D.A.

  • Find moles of the “given” using D.A.



Multiply #2 by the mole ratio of the “sought” to “given” (which is indicated by the coefficients in the balanced equation).

  • Multiply #2 by the mole ratio of the “sought” to “given” (which is indicated by the coefficients in the balanced equation).



Use Dimensional Analysis to find the desired units for the “sought.”

  • Use Dimensional Analysis to find the desired units for the “sought.”



Ex 2: How many grams of oxygen gas are required to react completely with 14.6 grams of solid sodium to form sodium oxide, Na2O(s)?

  • Ex 2: How many grams of oxygen gas are required to react completely with 14.6 grams of solid sodium to form sodium oxide, Na2O(s)?



Ex 3: How many grams of copper(II) will be required to completely replace silver from 208 mL of a 0.100 M solution of silver nitrate?

  • Ex 3: How many grams of copper(II) will be required to completely replace silver from 208 mL of a 0.100 M solution of silver nitrate?



Ex 4: A camping lantern uses the reaction calcium carbide (CaC2), a solid, and water to produce acetylene gas, C2H2(g), and calcium hydroxide. How many grams of water are required to produce 1.55 moles of acetylene gas?

  • Ex 4: A camping lantern uses the reaction calcium carbide (CaC2), a solid, and water to produce acetylene gas, C2H2(g), and calcium hydroxide. How many grams of water are required to produce 1.55 moles of acetylene gas?





4Fe + 3O2  2Fe2O3

  • 4Fe + 3O2  2Fe2O3

  • We usually have more of one reactant… we say that it’s

  • “in excess” (INXS)

  • This means we’ll run out of the other reactant… we say that it’s the

  • “limiting reactant”

  • Which reactant from our original rxn was INXS? Which was limiting?



How many bikes can be made from 10 frames and 16 wheels?

  • How many bikes can be made from 10 frames and 16 wheels?

  • 1 frame + 2 wheels  1 bike

  • MAKES 8 BIKES

  • with 2 FRAMES LEFTOVER!



Ex: How many moles of AlCl3 are formed from 40.0 g of Al and 213 g of Cl2?

  • Ex: How many moles of AlCl3 are formed from 40.0 g of Al and 213 g of Cl2?

  • 2 Al(s) + 3 Cl2(g)  2 AlCl3(s)

  • To solve, use the m/c ratio method:

  • moles of reactant (from given data)

  • coefficient of the reactant (from rxn)



How much Cl2 in grams from the previous problem is INXS (left over)?

  • How much Cl2 in grams from the previous problem is INXS (left over)?

  • A. Find the m/c ratios to determine limiting reactant

  • B. Calculate sought units (using stoich) and using the LR as the given

  • C. Calculate the mass of the reactant INXS that was actually used in the rxn (classic stoich)

  • Compare B and C (subtraction)



When you solve a classic stoic problem, you are assuming 100% yield

  • When you solve a classic stoic problem, you are assuming 100% yield

  • In the lab, you don’t usually get 100% yield



Theoretical Yield

  • Theoretical Yield

  • amount of product formed when the limiting reactant is completely consumed

  • assumes 100% yield

  • solving a stoic problem gets you this

  • Actual Yield

  • the amount of product actually recovered in the reaction.

  • Percent Yield

  • Actual yield (100)

  • Theoretical yield



Ex: Oil of Wintergreen (methyl salicylate) is made by the following process:

  • Ex: Oil of Wintergreen (methyl salicylate) is made by the following process:

  • C7H6O3 + CH3OH  C8H8O3 + H2O

  • A chemist starts with 1.75 g of salicylic acid and an excess of methanol. The chemist only yields 1.42 g of the sweet smelling stuff. Calculate the % yield!!!




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