Question

Cryolite, Na3AlF6(s), an ore used in the production of aluminum, can be synthesized using aluminum oxide. Balance the equation.

Al2O3(s)+6NaOH(l)+12HF(g)------>2Na3AlF6+9H2O(g)

If 16.8 kilograms of Al2O3(s), 56.4 kilograms of NaOH(l), and 56.4 kilograms of HF(g) react completely, how many kilograms of cryolite will be produced?

Which reactants will be in excess?

What is the total mass of the excess reactants left over after the reaction is complete?

Answer 1

we know that

moles = mass / molar mass

so

moles of Al203 = 16.8 x 1000 / 102

moles of Al203 = 164.706

moles of NaOH = 56.4 x 1000 / 40

moles of NaOH = 1410

moles of HF = 56.4 x 1000 / 20

moles of HF = 2820

now

consider the given reaction

Al203 + 6 NaOH + 12 HF ---> 2 Na3AlF6 + 9 H20

choose one reactant

let it be NaOH

now

from the above reaction

moles of Al203 required = (1/6) x moles of NaoH

= (1/6) x 1410

= 235

moles of Al203 required = 235

but only 164 moles of Al203 is present

so

Al203 is limiting reagent

now

moles of HF required = 2 x moles of NaoH

= 2 x 1410

moles of HF required = 2820

2820 moles of Hf is available

so

sufficient moles of   HF is available

finally

Al203 is the limiting reactant

and

NaOH , HF are in excess

now

consider the reaction

Al203 + 6 NaOH + 12 HF ---> 2 Na3AlF6 + 9 H20

from the reaction

moles of Na3AlF6 produced = 2 x moles of Al203 reacted

= 2 x 164.706

moles of Na3AlF6 produced = 329.412

now

mass of Na3AlF6 produced = 329.412 x 210

mass of Na3AlF6 produced = 69.17 kg

so

69.17 kg of Na3AlF6 is produced

now

from the reaction

moles of NaOH reacted = 6 x moles of Al203

= 6 x 164.706

= 988.236

moles of NaOH reacted = 988.236

moles of NaOH left = 1410 - 988.236 = 421.764

mass of NaOH left = 421.764 x 40

mass of NaOH left = 16.87 kg

now

moles of HF reacted = 12 x moles of Al203

= 12 x 164.706

= 1976.472

now

moles of HF left = 2820 - 1976.472

moles of HF left = 843.528

mass of HF left = 843.528 x 20

mass of HF reacted = 16.87 kg

so

total mass of excess reactants left = 16.87 + 16.87 = 33.74 kg