Stoichiometry

Balancing Hints:Balance the metals first.Balance the ion groups next.Balance the other atoms.Save the non ion group oxygen and hydrogen until the end.

Balance the following equations;

__Ca + __H2O → __H2 + __ Ca(OH)2

__ Cu + __ O2 → __ CuO

__ Na + __ O2 → __ Na2O

__ Fe + __ HCl → __ FeCl2 + __ H2

__ Fe + __ Br2 → __ FeBr3

__ C4H8 + __ O2 → __ CO2 + __ H2O

Balance this equation showing the burning of methane below, to answer the following questions.

__ CH4 + __ O2 → __ CO2 + __ H2O

How many grams of oxygen are required to produce 2.23 g of carbon dioxide?

How many grams of water will be produced when 34.0 g of methane is burned?

1. Calculate the moles of CO2 produced (same as mols of C)

2. Calculate the moles of H2O produced Multiply this number by two to calculate the number of moles of H atoms present in the original compound.

3. Calculate the mass of C and H

4. If there is another element present (typically O) in the combusted substance then calculate its mass by subtracting the mass of C and H from the total mass of the combusted sample.

5. Once you have determined the mass of each piece of the original compound the problem can be solved just like an empirical formula problem.

Steps for Combustion Analysis Problems

Combustion AnalysisA sample of a common alcohol with a mass of

4.599 g, containing C, H and O, was combusted in excess oxygen to yield 8.802 g of CO2 and 5.394 g of H2O.

The alcohol contains only carbon, hydrogen, and oxygen. What is the empirical formula of the acid?

Limiting ReagentThe limiting reagent is the reactant in a

chemical reaction which limits the amount of products that can be formed.

The limiting reagent in a chemical reaction is present in insufficient quantity to consume the other reactant(s).

This situation arises when reactants are mixed in non-stoichiometric ratios.

Let’s Try This Problem Together H2(g) + O2(g) → H2O(l)

Calculate the stoichiometric ratio of moles H2 to moles O2

b. The moles of water created when 1.50 mol H2 is mixed with 1.00 mol O2

c. the limiting reactant (H2 or O2) for the mixture in (b)

Let’s Try This Problem TogetherFor the reaction: Na2O + H2O → NaOH

What weight of NaOH could be made from 12.4 g of Na2O and 42.1 g of H2O?

What would be the limiting reagent if 100 g each of Na2O and H2O were allowed to react?

Percent YieldTheoretical yield - The maximum amount of a

given product that can be formed when the limiting reactant is completely consumed.

Actual yield - amount produced in a reaction. Should be less than the theoretical yield and provided some where in the problem.

Percent yield – (the actual / theoretical yield) x 100%