Determining Moles and Particles from Mass of a Compound

[rachelmaddiee]

Homework Statement

I need help with a question

Relevant Equations

N/A

mass = 37.2 g AICI3 (given)
number of ions = AI3+ Ions (unknown)
number of ions = CI- Ions (unknown)
mass = g/formula unit AICI3 (unknown)
The ratio of AI3+ Ions to CI- Ions is 1:3
Molar Mass AICI3
(1 x 26.98 g/mol AI) + (3 x 35.45 g/mol CI) = 133.33 g/mol AICI3
molar mass = 133.33 g/mol AICI3
Divide the given mass of aluminum chloride by its molar mass.
37.2 AICI3/133.33 mol = 0.279 mol AICI3

Is this correct?

 

[chemisttree]

So you have moles of AlCl₃. Now you should write out the balanced equation showing the production of ions from the AlCl₃.

 

[Borek]

Note: it is not AICI₃, it is AlCl₃ (small L, not capital I). Please revise what the chemical symbols of elements are.

 

[epenguin]

You have got the number of moles of AlCl₃. Which we will consider made of Al³⁺ and Cl^- ions. The question (as I understand it) asks what is the number of these ions in the sample.

(Hint: a very large number).

 

[rachelmaddiee]

You have got the number of moles of AlCl₃. Which we will consider made of Al³⁺ and Cl^- ions. The question (as I understand it) asks what is the number of these ions in the sample.

(Hint: a very large number).

1 mole of aluminum ions and 3 moles of Chloride ions

 

[chemisttree]

1 mole of aluminum ions and 3 moles of Chloride ions

Nope. You really should just write out the ionization equation. It will help you visualize how to proceed.

 

[rachelmaddiee]

Nope. You really should just write out the ionization equation. It will help you visualize how to proceed.

Are you looking at question 36?

 

[chemisttree]

Yes.
When I was teaching AP Chemistry, I required my students to write out the relevant equation to help them visualize and organize their thoughts. I’m not being pedantic. I know it works. Try it yourself if you don’t believe me.

 

[rachelmaddiee]

Yes.
When I was teaching AP Chemistry, I required my students to write out the relevant equation to help them visualize and organize their thoughts. I’m not being pedantic. I know it works. Try it yourself if you don’t believe me.

I don’t understand what I’m looking for.

 

[chemisttree]

AB₂ —-> A⁺² + 2B ^-

This would be an example. Put what you are given above the equation and what you need to calculate beneath the equation.

Like this:

3.2 g
AB₂ —-> A⁺² + 2B ^-
? mol ?mol ?mol
? # ? # ? #

 

[epenguin]

I don’t understand what I’m looking for.

If I ask how many atoms there are in a mole of an element does that help make sense of the Question?

 

[chemisttree]

If I ask how many atoms there are in a mole does that help make sense of the Question?

Nowadays they are asked for “how many particles” rather than how many atoms or molecules. It needlessly complicates things IMO but that’s the way it is.

 

[rachelmaddiee]

1 mole = 6.02 x 10^23 atoms

 

[chemisttree]

1 mole = 6.02 x 1023 atoms

1 mole = 6.02 x 10²³ atoms
1 mole = 6.02 x 10²³ particles

 

[rachelmaddiee]

1 mole = 6.02 x 10²³ atoms

Sorry, a mistake!

 

[rachelmaddiee]

AB₂ —-> A⁺² + 2B ^-

This would be an example. Put what you are given above the equation and what you need to calculate beneath the equation.

Like this:

3.2 g
AB₂ —-> A⁺² + 2B ^-
? mol ?mol ?mol
? # ? # ? #

This is confusing me. I can’t find any examples in my book.

 

[chemisttree]

Which is why I’m going through it with you here.

 

[rachelmaddiee]

Which is why I’m going through it with you here.

37.2 g
AICI3 —> AI+3 + 3CI -

 

[rachelmaddiee]

Can you please give me an example of How should it be written when I get my result?

 

[chemisttree]

OK. You are asked to find the number of ions of aluminum in part a. To do that you must calculate the number of moles of Al first. You have already calculated the moles of AlCl₃ so you are on your way!

 

[chemisttree]

From the equation above how many moles of Al⁺³ are produced from each mole of AlCl₃?

 

[rachelmaddiee]

From the equation above how many moles of Al⁺³ are produced from each mole of AlCl₃?

133.34g/mol?

 

[chemisttree]

133.34g/mol?

No, that’s the formula weight. You notice there is a 1:1 relationship between AlCl₃ and Al⁺³. Each mole of AlCl₃ produces a mole of Al⁺³. Half a mole of AlCl₃ produces half a mole of Al⁺³. How about 0.279 moles of AlCl₃?

 

[rachelmaddiee]

No, that’s the formula weight. You notice there is a 1:1 relationship between AlCl₃ and Al⁺³. Each mole of AlCl₃ produces a mole of Al⁺³. Half a mole of AlCl₃ produces half a mole of Al⁺³. How about 0.279 moles of AlCl₃?

Yes, I’ve solved for. That

 

[chemisttree]

Ok then. How many moles of Cl^- do you get from 0.279 moles of AlCl₃?

 

[rachelmaddiee]

Ok then. How many moles of Cl^- do you get from 0.279 moles of AlCl₃?

Wouldn’t it be 0.279 moles too?

 

[chemisttree]

Wouldn’t it be 0.279 moles too?

Each mole of AlCl₃ produces how many moles of Cl^-? Refer to the equation.

 

[rachelmaddiee]

Each mole of AlCl₃ produces how many moles of Cl^-? Refer to the equation.

3?

 

[chemisttree]

Right! So how many moles from 0.279 moles of AlCl₃?

 

[rachelmaddiee]

Right! So how many moles from 0.279 moles of AlCl₃?

I don’t. Understand how to find that?

 

[chemisttree]

Half a mole of AlCl₃ would produce 3 X 1/2 or 1.5 mol of Cl^-.

 

[rachelmaddiee]

Half a mole of AlCl₃ would produce 3 X 1/2 or 1.5 mol of Cl^-.

So it’s 1.5?

 

[chemisttree]

Yeah, IF you had half a mole of AlCl₃...
So, how many moles from 0.279 moles of AlCl₃?

 

[rachelmaddiee]

Yeah, IF you had half a mole of AlCl₃...
So, how many moles from 0.279 moles of AlCl₃?

So 3 x 1?

 

[chemisttree]

So 3 x 1?

No. You would multiply the stoichiometric ratio by the number of moles given (or calculated in your case).