Situation 1) Limestone is decomposed by heating to quicklime and carbon dioxide.
ID: 1022666 • Letter: S
Question
Situation 1)
Limestone is decomposed by heating to quicklime and carbon dioxide. Calculate how many grams of quicklime can be produced from 1kg of limestone.
Now: on chegg solutions the calculation is :
Situation 2)
Hydrogen fluoride is used in the manufacture of Freons (which destroy ozone in the stratosphere) and in the production of aluminium metal. It is prepared by the reaction :
In one process 6.00kg of CaF2 are treated with an excess of H2SO4 and yield 2.86kg of HF. Calculate the percent yield of HF.
Now: on chegg solutions the calculation is:
And then the percent yield.....
My question is:
Why does it start sometimes with kg, sometimes with grams...?
When do i divide 1mol/grams and sometimes grams/mol...?
Why sometimes is it 2 mol HF/1mol CaF2 and not the other way around...?
Why is it Grams/mol for molecule then mol/grams for the other molecule in the same equation?
When do i know that i should write it 2mol per 1 mol or 1 mol per 2 mol etc...?
I am just trying to understand how to place my equation correctly at the start of the exercises of stoichiometry. Thank you!
Explanation / Answer
The units of molar mass is gram/mol .This means 1 mole of that substance weighs those many grams.
Eg: Molar mass of CH4 is 16 g/mol .This means 1 mole of CH4 weighs 16 grams .you can ask me why 16 grams.Answer is CH4 contains 1 mole of Carbon and 4 moles of H.
1 mole of Carbon weighs 12 grams and 4 moles of H weighs 4 grams. Totally 12+4 = 16 grams.
(1) The units of molar mass is gram/mol .So u start with grams only. You can observe that the equation above wrote it as 6.00 x 103 grams instead of kg because the other unit is 1 mol /78 g.
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I will tell you how to start doing this type of problems.
step-1: Calculate number of moles of CaF2.
Molar mass of CaF2 =78 g/mol . This means 1 mole weighs 78 grams
So, we have 6.0 kg = 6x103 grams.
Number of moles = weight / molar mass = 6x103 grams./78 grams =76.92 moles
From recation, 1 mole of CaF2 formed 2 moles of HF in products.
So here we have 76.92 moles of CaF2.
So, moles o HF formed = 76.92 moles x(2 mol HF /1 mol CaF2) = 153.82 moles
But we have info that 2.86 kg was formed.
Here we have 153.82 moles.So now change this moles into grams.
This can be done by,
Mass of HF = 153.82 moles x (20.01 g /mol ) =3080 grams HF
now change into kg s as final answer given is in kg = 3080 grams x (1 kg /1000 kg) =3.080 kg
This is how we need to solve this type of problems