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HOMEWORK DUE MIErCOLES

• If you haven’t done so already, read chapter 3!

• P114 - 115: #22, #32, #34

StoichiometryThe quantitative study of chemical

reactions

Use stoichiometry to answer these questions:

How much product will form from a given amount of reactants?

How much of the reactants is necessary to form a given amount of product?

Stoichiometric Steps

Step 1• Predict products of a

reaction if they are not given to you

• Balance the coefficients of the reaction

Step 2• Use molar conversion to

change whatever is given (volume, mass or concentration) to moles

Step 3• Use the molar ratio from

the balanced reaction to convert the moles of what is given to the moles of what’s asked for.

Step 4• Use conversion factors

(moles mass, volume or M) to change the moles of what is asked for to the proper unit

Calculate the volume of NH3 formed at STP

when 5.0 kg of H2 react with excess N2

to form NH3

Calculate the number of molecules of

oxygen gas required to burn 3.0 g of

C5H10O5

Calculate the mass of solid product formed

when 18.4 g of MgBr2 is combined with a

solution containing excess K2CO3.

Limiting Reactant• The reactant that gets

used up

• The reactant that determines the amount of product formed

Excess Reactant•The reactant that Does Not get used up

When I give you quantities of more than one reactant:

You must figure out which one is limiting

3A + 2B A3B2

Which reactant is limiting?• Do Step 1 and then Step 2 for both A & B.• Pick A (your chemistry grade?)• Use the molar ratio that relates A to B to

determine how much of B would be needed to completely use up the moles of A

• If there are more than enough moles of B, A is limiting

• If there not enough moles of B, then B is limiting • Use limiting reactant for steps 3 & 4

Calculate the mass of glucose (C6H12O6)

formed when 880 g of carbon dioxide is

combined with 720 g of water in photosynthesis

Calculate the mass of BaSO4 formed when

104 g of BaCl2 is combined with 250 mL

1.00 M K2SO4

How to make a BLT sandwich:

2 PB(pieces bread)

3 TS(tomato slices)

5 BS(bacon slices)

2 LL(lettuce leaves)

+++

So reaction is:

• 2 PB + 3 TS + 5 BS + 2 LL 1 BLT

1 BLT

Masses of reactants + product:

• 1 PB = 50.0 g

• 1 TS = 60.0 g

• 1 BS = 20.0 g

• 1 LL = 5.0 g

• 1 BLT = 390.0 g

How many BLTs?

• PB = 3,356.7 g• TS = 4,789.2 g• BS = 2,789.4 g• LL = 789.2 g

Get answer in significant digits and then round down to whole number of BLTs.

Theoretical Yield• The amount determined

through stoichiometry

• The amount solved for on paper

Experimental Yield• The amount obtained in

the lab

• Actual yield

Percent yield• % Yield = (Exp/Theo) x 100 %

68 g NH3 was obtained when 140 g

of N2 reacts with excess H2. Calculate

percent yield.

510 g PH3 was obtained when 0.62 kg of P4 reacts with

excess H2. Calculate percent yield.

4.61 g of lead(II)iodide was obtained when 66.2 g of lead(II)nitrate was added to 750 ml 0.10 M

potassium iodide. Calculate the % yield.

Calculate the volume of oxygen gas at STP required to burn 12 kg of erythrose (C4H8O4)

Determine the volume of NH3 formed at STP

when 2.0 x 1027 molecules N2 reacts with

4.0 kg of H2:

Determine the volume of O2 released at STP

when 32 kg of Fe2O3 is purified making

Fe & O2

Calculate the mass of solid product formed when 41.6

g of barium chloride is added to 250 ml of 0.40 M potassium sulfate giving a

50.0 % yield:

Calculate the mass of solid product formed

when 2.00 g of calcium bromide is added to 250 ml of

0.40 M sodium sulfate: