My Chemistry Thread

[alchemy]

I'm a little confused when comparing two reactions involving acids and metal oxides/hydroxides.
I obtained the answers for both in two slightly different manners (as you do). My answers are correct, but can someone explain if my reasoning can be applied to this situation?

1) A solution of sulfuric acid is added to a solution of potassium hydroxide.
Unbalanced: H₂SO₄(aq) + KOH(aq) --> KSO₄ + H₂O(l)
Balanced: H₂SO₄(aq) + 2KOH(aq) --> K₂SO₄ + 2H₂O(l)
My inference here is: in order to balance the equation the 2- charge from the Sulphate anion in the Sulfuric acid must be brought down to conjoin with the Potassium (K) ion.

2) Black copper(II) oxide powder is added to dilute sulfuric acid.
Balanced: CuO(s) + H₂SO₄(aq) --> CuSO₄ + H₂O
My inference here is: in order to balance the equation the 2- charge need not be brought down from the Sulphate anion in the Sulfuric acid because of the characteristics/nature of Cu.

Can someone please explain why exactly the 2- charge from the Sulphate anion cannot be brought down to be associated with the Copper (Cu)? What characteristics of the Copper prevent it's charge association with Sulfuric acid in the latter example?
Also: what would be an eloquent scientific way to explain this, rather than my indirect reasoning?

[ECheong]

Hi, I'm sorry but I'm having a little bit of trouble understanding what you mean by 'brought down'?

I also presume that the questions are asking about balancing charges?

Just a little bit of clarification and then we can help you out

[alchemy]

I mean the 2- charge from the Sulfuric acid makes the potassium K₂.
The question asks to write a full chemical equation for the reactions.
Sorry, I didn't really explain the question well enough the first time around.

[ECheong]

haha no worries! Essentially, all it really is, is balancing charges.

A potassium atom, being in group 1 of the periodic table can, for most intents and purposes, only lose 1 electron. (This is because there's only 1 valence electron) This just means that K metal makes a K¹⁺ ion.

Inherently, the compound SO₄^2- comes with a 2- charge.

So, when the two combine, to make a neutral (0 charge) compound we'll need two +1s to negate that 2- charge. Hence, K2SO4.

In contrast, Cu typically makes +2 and +3 ions. We know in this equation it's a +2 ion because it's Copper (II) oxide. Since we know have a +2 Copper and a -2 Sulfate ion, they can combine to make a 0 charge compound CuSO₄.

At the core of it, what you want to be thinking when writing full equations is
a) do the number of elements balance
b) do the charges balance (the amount of charge you have on the left must equal what you have on the right)
c) states.

As a follow-on though, I must note that compounds don't always have to have a 0 charge. For example, the dissociation of an acid in water:

HCl+H₂O --> H₃O⁺ + Cl^-

Even though your charges on the hydronium (H3O+) and Chloride ions (Cl-) individually aren't 0, they add together to give the same amount of charge you started with; 0.

I hope that answers your question! If you need any clarification just shout out

[alchemy]

Question: Write the electron configuration of a Zn²⁺ ion.
Answer: 1s²2s²2p⁶3s²3p⁶3d¹⁰

My answer (incorrect): 1s²2s²2p⁶3s²3p⁶3d⁸4s²

Why is my answer incorrect?

[zvezda]

Question: Write the electron configuration of a Zn²⁺ ion.
Answer: 1s²2s²2p⁶3s²3p⁶3d¹⁰

My answer (incorrect): 1s²2s²2p⁶3s²3p⁶3d⁸4s²

Why is my answer incorrect?

I believe that youre correct on this one. Somebody correct me if im wrong. But the 4s subshell is at a lower energy level than the 3d. Where is this question from?

[Aurelian]

Question: Write the electron configuration of a Zn²⁺ ion.
Answer: 1s²2s²2p⁶3s²3p⁶3d¹⁰

My answer (incorrect): 1s²2s²2p⁶3s²3p⁶3d⁸4s²

Why is my answer incorrect?

In divalent and trivalent transition metal cations, the 4s orbital is of higher energy than the 3d orbitals, which is why the 4s orbitals are vacant in place of the 3d orbitals. This is in contrast to the atomic electronic structure of transition metals in which the 3d orbitals are higher in energy (which, I presume, quite reasonably formed the basis of your answer).

I wouldn't worry too much about it though...

[alchemy]

I believe that youre correct on this one. Somebody correct me if im wrong. But the 4s subshell is at a lower energy level than the 3d. Where is this question from?

It's from the Heinemann Chemistry 1 book, page 84. lol.   

[psyxwar]

If you're interested in doing some reading:

http://www.chemguide.co.uk/atoms/properties/3d4sproblem.html

[datfatcat]

The reason why it is 3d^10 instead of 3d^8 4s^2 is because it is more stable to have a completely filled 3d shell.

[alchemy]

Reviving this thread!

Quick question: Does electronegativity decreases down the periodic table because of there being a greater atomic radius and more shielding? Is it okay to use the term 'more (or less) shielding' when describing periodic trends?

[IndefatigableLover]

Reviving this thread!

Quick question: Does electronegativity decreases down the periodic table because of there being a greater atomic radius and more shielding? Is it okay to use the term 'more (or less) shielding' when describing periodic trends?

The properties of electronegativity all depend on the attraction between the negative outer-shell electrons and the positive nucleus. When you're saying about the atomic radius, it does increase going down a period which also means that there are more shells shielding the nucleus from the outer-electrons. The attraction between the nucleus and the outer-electrons decrease as a result of the greater atomic radius due to the increase in amount of shells when going down a period.

And I think when saying 'more (or less) shielding' you should mention shells in there as well when you're describing periodic trends imo...

[alchemy]

Why is it that cyclic ethenes don't have double bonds and are actually saturated with hydrogens? For example, the cyclic version of C₄H₈ exhibits this, and I still don't quite understand why.

[Yacoubb]

Why is it that cyclic ethenes don't have double bonds and are actually saturated with hydrogens? For example, the cyclic version of C₄H₈ exhibits this, and I still don't quite understand why.

Hmm..

Okay so cyclic pentane is C5H10. CnH2n is the general formula for a cyclic alkane. So in fact, the reason you may have seen ONLY single bonds, and the compound saturated with hydrogens, is because it is in fact a cyclic alkane (explained by C4H8).

[alchemy]

Hmm..

Okay so cyclic pentane is C5H10. CnH2n is the general formula for a cyclic alkane. So in fact, the reason you may have seen ONLY single bonds, and the compound saturated with hydrogens, is because it is in fact a cyclic alkane (explained by C4H8).

So if you were asked to draw the structural formula of benzene, and you had never seen how it looked like before, what would be your procedure of doing so? I don't understand why it is the way it is, and not the other cyclic version (previously assumed to be correct) which has all carbons linked by double bonds.