I’m hiring!

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# I’m hiring! - PowerPoint PPT Presentation

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!

• 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 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
Calculate the mass of glucose (C6H12O6) formed when 880 g of carbon dioxide is combined with 720 g of water in photosynthesis
How to make a BLT sandwich:

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 %
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.
Determine the volume of NH3 formed at STP when 2.0 x 1027 molecules N2 reacts with 4.0 kg of H2:
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: