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I’m hiring!. Homework Graders Pay = 1 extra credit point/10 papers graded Qualifications : No TUs, BD, LD Availability before/after school or 5 th period lunch. No nepotism/cronyism will be tolerated. HOMEWORK DUE MIErCOLES. If you haven’t done so already, read chapter 3!

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I’m hiring!

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### I’m hiring!

• Pay = 1 extra credit point/10 papers graded

• Qualifications:

• No TUs, BD, LD

• Availability before/after school or 5th period lunch.

• No nepotism/cronyism will be tolerated

### HOMEWORK DUE MIErCOLES

• P114 - 115: #22, #32, #34

### Stoichiometry

The 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?

### 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 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  A3B2Which reactant is limiting?

• Do Step 1 and then Step 2 for both A & B.

• 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

2 LL

(lettuce

leaves)

5 BS

(bacon

slices)

3 TS

(tomato

slices)

2 PB

(pieces

+

+

+

### 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.

### 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: