Limiting and Excess

Reagents

Concerned with identifying the identity of a substance

Or whether a specific substance is present

i.e. flame test, litmus tests

Qualitative Analysis

Determining the quantity (mass or concentration) of a specific substance present in a sample.

i.e. titrations, precipitation mass

Quantitative Analysis

Mass cannot be created or destroyed, it is merely rearranged in space, and changed into different types of particles.

Law of Conservation of Mass

Quantitative analysis can be used to verify the law of conservation of mass

Limiting Reagents

Sometimes 1 of the 2 reactants is not completely used up in a chemical reaction…

That’s the LIMITING reagent!

Limiting Reagent

1. Write a Balanced Equation for the Reaction2. Determine the 2 Reagents involved in the Reaction3. Using your 2 givens, Separately solve for your

unknown4. The species that gives the smaller amount of your

unknown is your Limiting Reagent5. Use your Limiting Reagent to Figure out how much of

your Excess Reagent will Actually React

STEPS TO SOLVING LIMITING REAGENT

PROBLEMS:

If 20.0mL of 3.0mol/L H2SO4(aq) is added to 15mL of 5.0mol/L KOH(aq), what mass of water can form?

Example 1:

350g of KOH(s) is added to 1.00L of 6.0mol/L of H3PO4(aq). How many moles of which reagent is in excess?

Example 2:

10.0L of nitrogen gas at 105kPa and 35C are mixed with 33.5L of hydrogen gas at 95.0kPa and 40C and ammonia gas is formed. What mass of ammonia gas will form?

Example 3:

5.00g of NaOH(s) is added to 50.0mL of 1.25mol/L HNO3(aq). Calculate the mass of water that forms. Determine your Limiting and Excess Reagents. Finally, use your LR to determine how much excess reagent is present.

Example 4