𝐻2+𝑂2−−→𝐻2𝑂How many grams of water will 5

grams of Oxygen produce?

5 grams of Hydrogen?

Tonight's Homework:

Finish Lab Report

pg 259 Numbers 2-10

Lab Report

• Purpose• Procedure• Data• Calculation (mass salt+dish)–(mass dish)• Results• Questions/Conclusion

Limiting Reactant

Percent Yield

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A Word About Mass Conversions

• Calculating the mass-mass conversion between compounds in a chemical reactions is not something that will disappear now that we are moving on

A Word About Mass Conversions

• Calculating the mass-mass conversion between compounds in a chemical reactions is not something that will disappear now that we are moving on

• If you can not calculate conversions from mass-mass, mass –mole , mole-mole…..

A Word About Mass Conversions

• Calculating the mass-mass conversion between compounds in a chemical reactions is not something that will disappear now that we are moving on

• If you can not calculate conversions from mass-mass, mass –mole , mole-mole…..

• You Will Fail

Consider the following reaction

2 H2 + O2 2 H2O

Reactants are combined in perfect proportions

6 molecules 6 molecules3 molecules

In reality this never happens

6 molecules 6 molecules3 molecules

Consider

4 molecules 4 molecules +leftover oxygen

3 molecules

Consider

LIMITING REACTANT

Amount ofPRODUCT is determined by limiting reactant

EXCESS REACTANT

Consider

6 molecules 4 molecules +leftover hydrogen

2 molecules

Consider

EXCESS REACTANT

Amount ofPRODUCT is determined by limiting reactant

LIMITING REACTANT

Given 24 grams of O2 and 5.0 grams of H2 determine the mass of H2O produced.

2 H2 + O2 2 H2O

the mass of H2O produced will be determined by the

limiting reactant - do TWO calculations

Two Calculations

Two Calculations• Calculate the amount of product each reactant

would produce

Two Calculations• Calculate the amount of product each reactant

would produce

• In this case convert grams of O2 to grams of H2O

Two Calculations• Calculate the amount of product each reactant

would produce

• In this case convert grams of O2 to grams of H2O

• Then convert grams of H2 to grams of H2O

Two Calculations• Calculate the amount of product each reactant

would produce

• In this case convert grams of O2 to grams of H2O

• Then convert grams of H2 to grams of H2O

• Whichever will produce the least amount

of water will be the limiting reactant

calculation for 24 grams of O2

24 g O2 2 H2O 18.0 g mol-1

32.0 g mol-1 1 O2

= 27 g of H2O

calculation for 24 grams of O2

24 g O2 2 H2O 18.0 g mol-1

32.0 g mol-1 1 O2

= 27 g of H2O

calculation for 5.0 grams of H2

5 g H2 2 H2O 18.0 g mol-1

2.0 g mol-1 2 H2

= 45 g of H2O

calculation for 24 grams of O2

24 g O2 2 H2O 18.0 g mol-1

32.0 g mol-1 1 O2

= 27 g of H2O

calculation for 5.0 grams of H2

5 g H2 2 H2O 18.0 g mol-1

2.0 g mol-1 2 H2

= 45 g of H2O

O2 is the LIMITING REACTANT and determines the amount of product

H2 is the EXCESS REACTANT (some would be left over)

How much hydrogen gas would be left over? To calculate, first determine how much reacts with all of the oxygen

How much hydrogen gas would be left over? To calculate, first determine how much reacts with all of the oxygengiven 24 grams of O2

24 g O2 2 H2 2.0 g mol-1

32.0 g mol-1 1 O2

= 3.0 g of H2

3.0 g of H2 reacts so

How much hydrogen gas would be left over? To calculate, first determine how much reacts with all of the oxygengiven 24 grams of O2

24 g O2 2 H2 2.0 g mol-1

32.0 g mol-1 1 O2

= 3.0 g of H2

3.0 g of H2 reacts so

5.0 g – 3.0 g = 2.0 g of hydrogen remains

Re-Cap

• What steps do you take to convert the mass of one substance to the mass of another in a chemical reaction?

• What steps do you take to determine which substance will be the limiting reactant in a reaction?

Percent Yield

2 AuCl3 +3 Pb 3 PbCl2 + 2 Au

Enoch the Red, an alchemist, wants to try to turn lead into gold (which you can’t do chemically). He finds that mixing lead with an unidentified compound (gold III chloride) actually produces small amounts of gold. The reaction is as follows:

Percent Yield

2 AuCl3 +3 Pb 3 PbCl2 + 2 Au

Enoch reacts 14.0 g of gold III chloride with excess lead metal. What would be the maximum, THEORETICAL yield of this reaction?

Percent Yield

2 AuCl3 +3 Pb 3 PbCl2 + 2 Au

Enoch reacts 14.0 g of gold III chloride with excess lead metal. What would be the maximum, THEORETICAL yield of this reaction?

Percent Yield

2 AuCl3 +3 Pb 3 PbCl2 + 2 Au

Enoch reacts 14.0 g of gold III chloride with excess lead metal. What would be the maximum, THEORETICAL yield of this reaction?

given 14.0 g of AuCl3

14.0 g AuCl3 2 AuCl3196.97 g mol-1

303.5 g mol-1 2 Au = 9.09 g Au

Percent Yield Enoch recovers only 1.05 g of gold from the reaction. This could be for many different reasons

some product was lost in the recovery process

the reaction did not go to completion

the AuCl3 is not pure

Percent Yield the percentage yield expresses the proportion of the expected product that was actually obtained.

actual% yield= ×100%

theoretical1.05

% yield= ×100%=11.6%9.09

Baking Soda Lab

• In the baking soda lab, the formula for the reaction should be :

• NaHCO3 + HCl ------> NaCl + CO2 + H2O 

• Balance the equation• Find the molar masses of

NaHCO3 & NaCl.

• Use the mass from you lab (mass baking soda) to calculate theoretical yield of NaCl

• What do we need to calculate the percent yield now that we have the theoretical yield?

Lab Reports

• The discussion questions were designed to have you calculate a theoretical yield and calculate a percent yield from your actual result.

Finding Limiting Reactant

• Determine the theoretical yield based on the masses of each reactant

• Whichever produces the least amount is your limiting reactant

Finding Theoretical Yield

• Use the mass-mass conversion from the limiting reactant to the desired product

• The product produced by the mass of the limiting reactant is the theoretical yield

Finding Percent Yield

• Use theoretical yield from your mass-mass (gram-gram) calcualtions

• Make sure you have the correct limiting reactant

• Divide the actual yield (given)

by the theoretical yield (from calculation)