👂What’s
that noise? Listen closely and you’ll
hear it.
👏 That’s me doing jumpy claps because it’s stoich time again, baby!
We
will attack these new stoichiometry problems in the same manner as in the
past. The only difference is in the
equations we have available.
We
will use what we had from before:
n = m/M
and add it to one of our recent
acquisitions:
PV = nRT
Notice that both
equations contain the all-important, n, or number of moles. This is vital because stoichiometry hinges
on the use of mole ratios.
Please also note
that we could employ %Y = (AY/TY)x100 and/or N = nNA, depending on
the situation.
So,
let’s try this thang:
- Create a balanced equation.
- List data (known/unknown) in columns.
- Using the mass of the reactant, combined with its molar mass, determine the number of moles.
- Set up a mole ratio between known substance and unknown substance to find number of moles of unknown substance.
- Using the moles of the unknown substance, combined with the conditions, determine the volume of that substance.
*****As with the last time we did stoichiometry, I'm going to harp on format. Correct format is non-negotiable. You WILL lose marks (perhaps a lot of them) if your format isn't pristine.*****
ex. Hot magnetic iron oxide, Fe3O4,
reacts with hydrogen gas to produce iron and water vapour. What volume of hydrogen, measured
at SATP, is required to react completely with 40.0 g of magnetic iron oxide?
Fe3O4(s) + 4H2(g) →
3Fe(s) + 4H2O(g)
m
= 40.0 g V = ?
M
= 231.55 g/mol T = 298.15 K
n
= m/M P = 100.0
kPa
= 40.0
g n = 0.691 mol
----------------- V = nRT/P
231.55 g/mol = 0.691 mol(8.314 kPa×L/K×mol)(298.15
K)
= 0.173 mol ---------------------------------------------------
100.0 kPa
= 17.1 L
nFe3O4/1 = nH2/4
nH2
= 4(0.173 mol)
=
0.691 mol
Now, go on to the Gas Stoichiometry, Part 2 lesson.
Homework:
- What mass of pure potassium chlorate must be heated to produce 50 mL of oxygen gas, collected at STP conditions? The other product of the reaction is potassium chloride.
- What volume of hydrogen gas, at STP, could be prepared by treating 4.86 g of magnesium with excess hydrochloric acid?
- Sulfur burns in oxygen to produce sulfur dioxide. What volume of sulfur dioxide, at STP, would be formed by burning 1.6 g of sulfur?
- How many litres of ammonia, measured at STP, could be made from 75 g of magnesium nitride? Mg3N2 + 6 H2O → 3Mg(OH)2 + 2 NH3
- In an experiment, 7.84 g of sulfuric acid reacts with potassium carbonate to produce potassium sulfate, water and carbon dioxide gas. Determine the mass of potassium carbonate consumed. Determine the mass of potassium sulfate formed. Determine the volume of carbon dioxide evolved at STP.
- What mass of magnesium would be required to produce 250 mL of hydrogen gas, at STP, by reaction with hydrochloric acid?
- Hydrogen gas is produced when magnesium reacts with hydrochloric acid. Calculate the mass of magnesium required to produce 1.78 L of hydrogen gas, if the gas is collected at 97 kPa and 28°C.
- What volume of sulfur dioxide, measured at 17°C and 98.4 kPa, would be formed by burning 1.60 g of sulfur?
- Carbon burns in air, producing carbon dioxide gas.What mass of carbon dioxide gas will be produced when 3.60 g of carbon is burned? Calculate the volume of the carbon dioxide at STP. Calculate the volume of the carbon dioxide gas at 191.5 kPa and 200°C.
Answers:
Note: The answer to question #1 should be rounded to 1 SD. So, it should read m = 0.002 g.
