Homework questions thread

[Aurelian]

Reason for the relationship between mass and energy required to stretch a bond is based on quantum theory, from memory.

huh?

Lol. Just ignore that, you don't need to worry about it

Thushan, I assume you are talking about how the intensity of the absorption band is directly proportional to the derivative of the molecular dipole moment (which is affected by the molecule's polarizability) in relation to the normal placement?

-_-

[Comatose]

hey guys im having trouble with this question:
a precipitate of Fe₂O₃ of mass 1.43g was obtained by treating a 1.5L sample of bore water. What was the concentration of iron, in mol L^-1 in the water?
cheers

[Kanon]

Engage Panic Mode!
Could someone help me out with this one?

How many atoms are present in 5.00 mole of Copper Sulfate?

How I would have approached this was



However, the solutions have it as



Where'd the 6 come from in the solutions?

[jasoN-]

^ CuSO4 contains 6 atoms per molecule
so 5 mols of CuSO4 contains 5*6.023E23 molecules

6 atoms : 1 molecule
x atoms : 5*6.023E23 molecules

x = 5*6.023E23*6 = 1.81E25

[Kanon]

^ CuSO4 contains 6 atoms per molecule
so 5 mols of CuSO4 contains 5*6.023E23 molecules

6 atoms : 1 molecule
x atoms : 5*6.023E23 molecules

x = 5*6.023E23*6 = 1.81E25

I think you kind sir, you are a gentleman and a scholar,

[Aurelian]

Engage Panic Mode!
Could someone help me out with this one?

How many atoms are present in 5.00 mole of Copper Sulfate?

How I would have approached this was



However, the solutions have it as



Where'd the 6 come from in the solutions?

Copper sulfate = CuSO4

There are 6 *atoms* in every molecule# of copper sulfate; hence, multiply by 6.

#nb, not actually really 'molecules' (ionic salt)

[Kanon]

Thank you Aurelian
I'm stuck again haha, the next question asks

How many ions are present in 2.00 mole of Na₃PO₄?

I don't see any ions in that though? Would it be possible to say that we multiply it by 8 as there are 8 atoms per molecule ionic thingy?
I'm so sorry, i'm pretty bad at Chemistry.

[jasoN-]

Ions in are (phosphate) and (sodium) ions

[KOM]

hey guys im having trouble with this question:
a precipitate of Fe₂O₃ of mass 1.43g was obtained by treating a 1.5L sample of bore water. What was the concentration of iron, in mol L^-1 in the water?
cheers

You work out the mol of Fe₂O₃ and since there are 2 atoms of iron per Fe₂O₃ , n(Fe) = double of n(Fe₂O₃ )
From there, n(Fe)/1.5L will give you the concentration of Fe in mol L^-1

[soccerboi]

Hi guys, im stuck on this:

25cm^3 of a mixture of carbon monoxide and carbon dioxide were mixed with oxygen, which increaded the total volume to 55cm^3. When the mixture was exploded, the total volume was reduced to 50cm^3. Calculate the percentage by volume of carbon monoxide in the original mixture of carbon monoxide and carbon dioxide. Ans is 40%

[KOM]

Hi guys, im stuck on this:

25cm^3 of a mixture of carbon monoxide and carbon dioxide were mixed with oxygen, which increaded the total volume to 55cm^3. When the mixture was exploded, the total volume was reduced to 50cm^3. Calculate the percentage by volume of carbon monoxide in the original mixture of carbon monoxide and carbon dioxide. Ans is 40%

I believe that you assume combustion between CO and O₂
So 2CO + O₂ --> 2CO₂
so you have to lose 5cm^3 to have a total volume of 50cm^3, therefore 5cm^3 of the excess O₂ is used up meaning 10cm^3 of CO was combusted, hence originally there was 10cm^3 of CO
10/25 = 0.4 = 40%

Hope that makes sense!

[soccerboi]

Can you explain your thought process on how u derived the equation? I have trouble deriving equatoins for these types of questions.. Like, i dont understand how to know what are the products, what do u think about when u come up with equations for these types of questions?

[KOM]

Can you explain your thought process on how u derived the equation? I have trouble deriving equatoins for these types of questions.. Like, i dont understand how to know what are the products, what do u think about when u come up with equations for these types of questions?

Well the mixture was exploded, so you'd assume a combustion reaction.
To combust something, you end up with carbon dioxide. So my thinking process was, ok, it shouldn't be a reactant then. Oxygen is always needed, so i wrote up CO + Oxygen --> Carbon Dioxide
and then I went from there

[soccerboi]

Oh okay thanks alot, btw wouldnt H20 be a product of combustion or is it excluded in this case because it is an explosion?

[Panicmode]

Oh okay thanks alot, btw wouldnt H20 be a product of combustion or is it excluded in this case because it is an explosion?

Water cannot be a product as there was no hydrogen in any form in the tank. Water is usually formed when a hydrocarbon reacts because the hydrogen is able to react with oxygen to form water.

In this case, the only product possible would be carbon dioxide.