Lithium Hydroxide 0.602mole Calculation

[chawki]

Homework Statement

Homework Equations

The Attempt at a Solution

a)
Li₃N + 3 H₂O --------> 3 LiOH + NH₃
7g---------------------m
34.83g----------------3*23.94

m=14.43g
n=14.43/23.94=0.602mole.

 

[Borek]

0.602 mole is not an answer to any of the questions asked. 14.4g is much better.

 

[chawki]

But in part a, they asked to find number of moles.

 

[Borek]

Sorry, my mistake, somehow I read they just asked about mass in the first part of the question, and moles in the second. That's partially because you entered question as an image - I had to switch between the answer and the question, it doesn't help.

 

[chawki]

Ok, I'm sorry too for putting the question on image.

If the number of moles in part a is correct, please give me a hint how should approach part b, where they ask how many moles of ammonia can be formed if 2.5moles of lithium nitride is mixed with 4.5moles of water

 

[Borek]

Limiting reagents.

 

[chawki]

n= (18.01*7)/(54+34.83)
n=1.419 mole.

 

[Borek]

No. Forget about masses, calculate just number of moles.

 

[chawki]

n=7/4 mole ?

 

[Borek]

Where did you got 7 and 4 from?

Take a look at the reaction equation.

http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations

How many moles of LiOH can be produced from 1 mole of lithium nitride? From 2.5 mole of nitride?

How many moles of LiOH can be produced from 1 mole of water? From 4.5 mole of water?

 

[chawki]

How many moles of LiOH can be produced from 1 mole of lithium nitride? From 2.5 mole of nitride?

How many moles of LiOH can be produced from 1 mole of water? From 4.5 mole of water?[/QUOTE]

From 2.5mole of lithium nitride, we have 2.5*3mole of LiOH
From 4.5mole of water , we have 4.5 mole of LiOH

 

[Borek]

From 2.5mole of lithium nitride, we have 2.5*3mole of LiOH
From 4.5mole of water , we have 4.5 mole of LiOH

So, which one is a limiting reagent and what is the final answer?

 

[chawki]

I really have no clue...

 

[Borek]

Have you read limiting reagent page that I linked to several posts earlier?

 

[chawki]

yes but i didn't understand it...sorry

 

[Borek]

H₂ + Cl₂ -> 2HCl

You mix 1 mole of hydrogen and 1000000 moles of chlorine - how many moles of HCl would you get?

 

[chawki]

H₂ + Cl₂ -> 2HCl

You mix 1 mole of hydrogen and 1000000 moles of chlorine - how many moles of HCl would you get?

Please tell me

 

[Borek]

Take a look at the reaction equation and stoichiometric coefficients.

How many moles of HCl can be produced from 1 mole of hydrogen? How many moles of Cl₂ are needed for that? Do we have that much chlorine?

How many moles of HCl can be produced from 1000000 moles of chlorine? How many moles of H₂ are needed for that? Do we have that much hydrogen?

 

[chawki]

Take a look at the reaction equation and stoichiometric coefficients.

How many moles of HCl can be produced from 1 mole of hydrogen? How many moles of Cl₂ are needed for that? Do we have that much chlorine?

How many moles of HCl can be produced from 1000000 moles of chlorine? How many moles of H₂ are needed for that? Do we have that much hydrogen?

we can get 2 moles of HCl from 1 mole of hydrogen and 1 mole of Cl₂
i used to have a method like '' x-number of moles'' but i forgot it :(

 

[chawki]

so how many moles of HCl we get for mixing 1 mole of hydrogen and 1000000 moles of chlorine

 

[Borek]

No, you will not get the answer, you have to work it out. Try to answer all questions I have asked, it should become obvious what the final answer is. Answering 1 question out of 4 and hoping for a miracle won't get you far.

 

[symbolipoint]

The amount of product HCl will depend on the limiting reagent.

 

[chawki]

wanna give me an example ?

 

[QuarkCharmer]

[PLAIN]http://www.chem.tamu.edu/class/majors/tutorialnotefiles/cars.gif

In this example, you only need 32 tires to put those 8 car bodies to good use. Since there is excess tires after the reaction (cars getting the tires installed), the bodies are what limit the reaction.Sometimes it is hard to tell which of the reactants will limit the product. If that is the case, you need to use one given reactant and express it in terms of moles of the other reactant. If that is greater than the second given reactant, then you "need" more of that second reactant, and so that is the limited reactant.The ratio of H to Cl in your balanced equation is 1/1...

http://www.khanacademy.org/video/stoichiometry--limiting-reagent?playlist=Chemistry

 

[chawki]

So, which one is a limiting reagent and what is the final answer?

limiting reagent is H₂O because the ratio Li₃N/H₂O = 1/3 =2.5/(3*2.5) = 2.5/7.5
we have too much H2O than we need

 

[chawki]

the equation will be:
Li₃N + 3 H₂O ----> 3 LiOH + NH₃
we multiply by 1.5 in order to get 4.5 moles of the limiting reagent.
1.5 Li₃N + 4.5 H₂O ----> 4.5 LiOH + 1.5 NH₃
so we will get 1.5 mol of NH₃

i hope I'm right

 

[Borek]

limiting reagent is H₂O because the ratio Li₃N/H₂O = 1/3 =2.5/(3*2.5) = 2.5/7.5
we have too much H2O than we need

If water is a limiting reagent, we can't have too much of it.

so we will get 1.5 mol of NH₃

Surprisingly, this is a correct answer. As I am not able to follow your line of thinking I am not convinced it is not accidental.

 

[chawki]

If water is a limiting reagent, we can't have too much of it.



Surprisingly, this is a correct answer. As I am not able to follow your line of thinking I am not convinced it is not accidental.

ok well, isn't water the limiting reagent ?
I just watched that video and learned from it.

 

[Borek]

Water IS a limiting reagent, but it means there is not TOO MUCH of water, but NOT ENOUGH.

 

[chawki]

ahhh ok, i will try to understand that, and thank you again :)

 

[chawki]

so how many moles of HCl we get for mixing 1 mole of hydrogen and 1000000 moles of chlorine

we will get simply 1 mol, the other 999999 will not react

 

[Borek]

No, we will not get 1 mole of HCl.

Close, but no banana.

 

[chawki]

ok well, isn't water the limiting reagent ?
I just watched that video and learned from it.

we will need 1.2 moles of H₂O ?

 

[Borek]

Looks like you still don't understand anything. Limiting reagent is FULLY consumed.