Chem Stoichiometry Percent Yield

What is a Excess Reagent?

• amount you end with

• what you run out of first

• what you have left over

• what you start with

Answer explanation

You will have excess reactant left over when the reaction stops. You use up all of the limiting reactant which stops the reaction before the excess has been all used up.

CO (g) + O₂(g) → 2 CO₂ (g)
In the formation of CO₂ from CO and oxygen, how many Liters of CO₂ are produced by the reaction of 8 mols of O₂ with an excess of carbon monoxide?

• 0.178 L

• 358.4 Liters

• 704 grams

• 0.36 grams

Answer explanation

The actual answer is 358.4, but due to sig. figs. it must be rounded up to 400 L.

Tags

NGSS.HS-PS1-7

Using the following balanced equation: Fe₂O₃(s) + 3H₂(g) → 2Fe(s) + 3H₂O(l) How many moles of iron can be made from 6.0 moles H₂ assuming there is excess Fe₂O₃?

• 4.0 moles Fe

• 6.0 moles Fe

• 9.0 moles Fe

• 2.0 moles Fe

Tags

NGSS.HS-PS1-7

Which setup of conversion factors shows the correct process in determining how many grams of iron can be created if the reaction below starts with 6.50 moles of Mg? 3 Mg + 1 Fe₂O₃ → 3 MgO + 2 Fe

• a

• b

• c

• d

Before performing a lab, a scientist calculates that a reaction should produce 12.3 grams of product in an experiment. When the reaction is performed, the product has a mass of 10.1 grams. What is the percent yield?

• 82.1 %

• 17.9 %

• 122 %

• 1.22 %

What would be the correct numbers of products and leftovers? (In the order shown for the chemicals in the image)

• 4, 6, 6, 1

• 2, 3, 7, 4

• 2, 3, 1, 3

• 4, 6, 2, 5

Tags

NGSS.HS-PS1-7

When calculating the percent yield, what is the measured amount of a product obtained from a chemical reaction?

• mole ratio

• theoretical yield

• percentage yield

• actual yield

Using the following balanced chemical equation:

4 Al + 3 O₂ –> 2 Al₂O₃

How many moles of aluminum would be needed to completely react with 55.0 grams of O₂?

• 73.3 moles

• 0.938 moles

• 1.88 grams

• 2.29 moles

Tags

NGSS.HS-PS1-7

If 55.6 grams of sodium hydroxide react with excess calcium carbonate, how many grams of Na₂CO₃ are produced in this reaction?

CaCO₃ + 2 NaOH → Ca(OH)₂ + Na₂CO₃

• 73.7 grams

• 27.8 grams

• 10.5 grams

• 295 grams

Identify the limiting reagent when 6.00 moles HCl combines with 5.00 moles Mg to form MgCl₂.
 
1 Mg +  2 HCl --> 1 MgCl₂  +  1 H₂   
 

• Mg

• H₂

• MgCl₂

• HCl

Tags

NGSS.HS-PS1-7