Chem Stoichiometry Percent Yield

When reacting Na with Cl₂, we calculated that the theoretical yield should be 13 grams. Our actual yield was 12.5 grams. What is the percent yield?

• 90.4%

• 104%

• 96%

• 1.0%

Answer explanation

Tags

NGSS.HS-PS1-7

Theoretical yield = 73g
Actual yield = 62g
Calculate the percent yield.

• 2%

• 120%

• 85%

• 76%

Answer explanation

What does percent yield indicate?

• The amount of product we should get

• The efficiency of the lab

• The amount of product we actually got

• nothing

Answer explanation

% Yield tells the efficiency of your work - how close you were to the theoretical value you should have gotten

Tags

NGSS.HS-PS1-7

NGSS.HS-PS1-6

Some product may be lost during filtering causing your actual yield to be less than your theoretical yield.

• true

• false

Answer explanation

Anytime you "lose" product, your actual will be less than your theoretical b/c you lost some of the product.

Your actual will be higher than your theoretical if you add substances that are not the product - example measuring the filter paper & product, and not just the product.

Tags

NGSS.MS-PS1-5

What is a limiting reactant?

• the reactant that determines how much product can be made

• the reactant that is in excess

• the product that you can make the most of

• the amount of reactants that react with each other

Answer explanation

The limiting reactant LIMITS the amount of product that can be made, b/c the rxn stops when the limiting runs out...meaning no more product is made.

Tags

NGSS.HS-PS1-7

When 12 moles of O₂ reacts with 1.1 mole of C₁₀H₈ what is the limiting reactant?  C₁₀H₈ + 12 O₂ --> 10 CO₂ + 4 H₂O

• Oxygen

• C₁₀H₈

• Water

• Carbon Dioxide

Answer explanation

Tags

NGSS.HS-PS1-7

2H₂  +   O₂  →  2H₂O
How many moles of oxygen are consumed if 8 moles H₂ are used?

• 2

• 4

• 6

• 8

Answer explanation

H2 has a 2:1 ratio with oxygen (from the coefficients of the balanced equation)

So 8 moles of H2 means 4 moles of O2 are used.

2:1 = 8:X = 8:4

Tags

NGSS.HS-PS1-7

For the Balanced Reaction: 3 Mg + 1 Fe₂O₃ → 3 MgO + 2 Fe; What is the Ratio of moles of MgO to moles Fe?

• 3mol Mg / 2 mol Fe

• 2 mol Mg/ 3 mol Fe

• 1 mol Fe/ 2 mol Fe

• 3 mol MgO / 2 mol Fe

Answer explanation

Mole:mole ratios come from the coefficients of the balanced equation

2Na + 2H₂O → 2NaOH+ H₂
How many grams of hydrogen are produced if 120 g of Na are available?

• 5.3 g

• 2.6 g

• 690 g

• 45 g

Answer explanation

Tags

NGSS.HS-PS1-7

Cl₂ + 2 KBr → Br₂ + 2 KCl
How many grams of potassium chloride can be produced from 356 g of chlorine and 356 g of potassium bromide?

• 749 g

• 223 g

• 479 g

• 814 g

Answer explanation

When given 2 values, you must first determine the limiting reactant. Then you must do the conversion/stoichiometry using the starting amount of the limiting reactant.

Tags

NGSS.HS-PS1-7