Question

How many grams of potassium chloride must decompose to produce 69.9 milliliters of potassium metal, if the density of potassium is 1.78 g/mL?

KCl → K + Cl2

Answer 1

@Zale101

Answer 2

@Jhannybean

Answer 3

We are looking for he mass of KCl which will decompose and produce 69.9 ml of K. The density of K is already given which is 1.78 g/ml. Let's find the mass of Potassium.
We know that \(\large Density=\Large\frac{Mass}{Volume}\) , but we have the volume given which is 69.9 mL of K and density which is 1.78 g/mL
That means we solve for the mass by myltiply volumes to both sides canceling the volume from the right side

Answer 4

\(Mass= Density * Volume\)
Mass (K)= 69.9 mL*\(\Large\frac{1.78g}{1mL}\)
the mL will canceling out and we'll have the answer in grams for Potassium which is K.

Answer 5

@sleepyjess makes sense so far?

Answer 6

Yes

Answer 7

So now I would do 69.9*1.78?

Answer 8

Mass of K=124.42 g
Now, we need to convert this to moles. To do that, we divide the grams by the atomic weight of K which is 39.1g/mol.

\(124.42 g *\large\frac{1~mol}{39.1 g}= 3.182 mol~K\)

Answer 9

Yes, @sleepyjess

Answer 10

Now, we still need to know how many grams of KCl, we were only solving for K.

Answer 11

We got the moles of K though which will help us know the moles of KCl if we looked at the molar ratio from the balanced chemical equation \(KCl \rightarrow K+Cl_2\)

Answer 12

You know what's molar ratio between KCl and K?

Answer 13

No

Answer 14

there's 1 moles of K, and 1 moles of KCl in the equation, correct?

Answer 15

Molar ratio is 1 to 1 which tells us that there were moles of K produced that has the same amount of moles in KCl when decomposed . KCl has 3.182 mols as well.

Answer 16

Here's a better understanding of molar ratio http://www.occc.edu/kmbailey/Chem1115Tutorials/Molar_Ratios.htm

Answer 17

Ok, so there is 3.182 of each?

Answer 18

We had 3.182 mols of KCl before decomposing and after decomposing we produced 3.182 mols of K. So K and KCl has the same amount of mols, yes, by molar ratio.

Answer 19

Oh, ok

Answer 20

Now what's next?

Answer 21

the question is looking for grams of KCl and we already have the mols for KCl

Answer 22

We need to convert the mols into grams, correct?

Answer 23

grams/mol = molar mass/1 mol

Answer 24

Yeah, \(grams~KCl=3.182~mol(KCl)\Large \frac{74.56 g}{mole}\small(KCl)\)
Moles cancel out, that leaves us with multiplying 3.182 by 74.56 g to get the grams of KCl

Answer 25

237.25

Answer 26

yes