oxgyen + metals -> wdf? (1 Viewer)

[atrocityx]

okay so there one dot point in the syllabus
compare the mass changes in samples of metals when they combine with oxygen?

I DON'T GET IT D=
could someone explain?

there also one question i dont understand

1.00g of samples of lithium, calcium and zinc were heated in air to form oxides. calculate the percentage increase in mass you would expect for each metal (assuming complete reaction)

how do you find the percentage increase?
if the question asks for the mass of oxygen would you minus the amount of the metal oxide?

 

[maplestory]

okay so there one dot point in the syllabus
compare the mass changes in samples of metals when they combine with oxygen?

I DON'T GET IT D=
could someone explain?

there also one question i dont understand

1.00g of samples of lithium, calcium and zinc were heated in air to form oxides. calculate the percentage increase in mass you would expect for each metal (assuming complete reaction)

how do you find the percentage increase?
if the question asks for the mass of oxygen would you minus the amount of the metal oxide?

not so sure
but write the chemical equation first, in your case
4 Li + O2 -----> 2 Li2 O

find the moles of Li >> 1/6.941 = 0.1441 mol
moles of O2 >> 0.1441/4 = 0.0360 mol

mass of O2 >> 0.0360 x 32 = 1.1526g

ugh ... this alco confused meh

check some notes out from BOS resources, that will help u than i did
=)

 

[Gussy Booo]

Well the main thing behind it all, is that oxygen combines with the metal, therefore resulting in a greater mass.

So lets try and show this:

NB: Im not to sure on this either hehe.

So I'm going to work with Calcium.

Step 1) Write out the reaction in words
.'. Calcium+ Oxygen Gas -> Calcium Oxide

Step 2) Write out the symbols

Ca+ O2 (Oxygen is a gas, therefore it is in diatomic form) --> NaO (Calcium has a valency of +2, Oxygen has a valency of -2, so it simply becomes NaO

Step 3) Balance the equation
2Ca + O2 --> 2CaO

Step 4) Find the number of moles.
So we know the formula as N = Mass / Atomic Mass.
Therefore:

2N = 100/40.08
2N = 2.495.

But that's for 2 moles (the balanced equation says we have 2 moles of calcium), so you divide it by two to get :

1.2475 Moles.

-------
Now, we know that the metal has a mass of 100g, all we have to do on the RHS of the equation, is show that it has a greater mass.

Step 4) Work with the RHS
2Ca + O2 --> 2CaO

We have 2 moles of Calcium and Oxygen.
We can assume that we have 100G of Calcium, which is visible from the equation above.
So to find the mass of oxygen:

1.2475 = Mass/16
Mass of Oxygen = 19.96
So the mass of Calcium Oxide is 100+19.96 = 119.96.

I THINK THIS IS HOW YOU DO IT. I am not 100% sure.

One more thing I should note, according to the laws of reactions and matter, matter is not created or lost within a reaction. Therefore, the increase in mass is due to the joining together of Calcium and Oxygen.

 

[Aquawhite]

I had a practical assessment on doing this, we used magnesium and of course was transformed into magnesium oxide. Using the formula is the only way I can think of doing it in theoretical molar measurements unless you have a mass and then have the mass of the oxidised metal afterwards (but the question would be harder or different).

 

[Gussy Booo]

Aqua, was my explanation correct?
=[

 

[Aquawhite]

That's using 100 grams of the metal hehe... although the OP did ask for use with 1.00g lol XD hehe

It's perfectly fine as far as I can see.

Oh, and to do the percentage increase... pretty basic and simple. Divide the initial mass by the final mass and multiply by 100 ^_^

 

[maplestory]

Well the main thing behind it all, is that oxygen combines with the metal, therefore resulting in a greater mass.

So lets try and show this:

NB: Im not to sure on this either hehe.

So I'm going to work with Calcium.

Step 1) Write out the reaction in words
.'. Calcium+ Oxygen Gas -> Calcium Oxide

Step 2) Write out the symbols

Ca+ O2 (Oxygen is a gas, therefore it is in diatomic form) --> NaO (Calcium has a valency of +2, Oxygen has a valency of -2, so it simply becomes NaO

Step 3) Balance the equation
2Ca + O2 --> 2CaO

Step 4) Find the number of moles.
So we know the formula as N = Mass / Atomic Mass.
Therefore:

2N = 100/40.08
2N = 2.495.

But that's for 2 moles (the balanced equation says we have 2 moles of calcium), so you divide it by two to get :

1.2475 Moles.

-------
Now, we know that the metal has a mass of 100g, all we have to do on the RHS of the equation, is show that it has a greater mass.

Step 4) Work with the RHS
2Ca + O2 --> 2CaO

We have 2 moles of Calcium and Oxygen.
We can assume that we have 100G of Calcium, which is visible from the equation above.
So to find the mass of oxygen:

1.2475 = Mass/16
Mass of Oxygen = 19.96
So the mass of Calcium Oxide is 100+19.96 = 119.96.

I THINK THIS IS HOW YOU DO IT. I am not 100% sure.

One more thing I should note, according to the laws of reactions and matter, matter is not created or lost within a reaction. Therefore, the increase in mass is due to the joining together of Calcium and Oxygen.

*whistles* i have copied this .... =)

 

[Aquawhite]

I actually thought it would have been pretty obvious to do this ... :S lol. I think I just have a mind to figure out things in chemistry hehe (now I'm bragging).