Need help with chem questions

[koolaidman]

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I need help with the following two chem questions:

How many valence electrons are in the sulfur atom in a sulfate ion? Answer is twelve. How did they get that number?

PbBr2 has a concentration of 1x10^-5 M. What is the concentration of Pb? How do calculate this?

Thanks.

 

[vhlam]

How many valence electrons are in the sulfur atom in a sulfate ion? Answer is twelve. How did they get that number?

draw out the structure of the sulfate ion and count how many electrons are around just the sulfur atom. hint: wikipedia is your friend

 

[joonkimdds]

I need help with the following two chem questions:

How many valence electrons are in the sulfur atom in a sulfate ion? Answer is twelve. How did they get that number?

PbBr2 has a concentration of 1x10^-5 M. What is the concentration of Pb? How do calculate this?

Thanks.

My answers might be wrong but here is my guess.
PbBr2 has 1 mol and it's 10^-5M.
If you completely dissociate this, it's 1Pb + 2Br.
Pb has 1 mol so it also has 10^-5M.
but Br has 2 mol so it has 20^-5M.
*Plz correct me if I am wrong, and plz confirm if I am correct.

Sulfur is 6th group so I think it should have 6 valence electron. I don't know how 12 is possible, hm... are you sure about that?
I know that sulfur can be more than octet, meaning it can have more than just 4 single bonds.
Sulfate has 2 double bonds and 2 single bonds around Sulfur but I think that doesn't change the fact that sulfur itself should have 6 valence electron.

 

[klutzy1987]

My answers might be wrong but here is my guess.
PbBr2 has 1 mol and it's 10^-5M.
If you completely dissociate this, it's 1Pb + 2Br.
Pb has 1 mol so it also has 10^-5M.
but Br has 2 mol so it has 20^-5M.
*Plz correct me if I am wrong, and plz confirm if I am correct.

Sulfur is 6th group so I think it should have 6 valence electron. I don't know how 12 is possible, hm... are you sure about that?
I know that sulfur can be more than octet, meaning it can have more than just 4 single bonds.
Sulfate has 2 double bonds and 2 single bonds around Sulfur but I think that doesn't change the fact that sulfur itself should have 6 valence electron.

2: As oxygen has 2 valence elctrons and there is a charge of -2 that makes 10 electrons. Now 8 of them are shared. So sulfur has 10 valence electrons but 8 are sared so in reality it has 4+2=6.

1) Pbr2 does not dissociate at all because it has lead. Therefore the concentration of Pb is 0 and the concentratuion of Br is 0.

 

[koolaidman]

2: As oxygen has 2 valence elctrons and there is a charge of -2 that makes 10 electrons. Now 8 of them are shared. So sulfur has 10 valence electrons but 8 are sared so in reality it has 4+2=6.

1) Pbr2 does not dissociate at all because it has lead. Therefore the concentration of Pb is 0 and the concentratuion of Br is 0.

Ok, I understand the valence electron question. However, how do I calculate the concentration of the ions if the molecules do dissociate given the concentration of the compound. For example, CaCl2.

 

[klutzy1987]

Ok, I understand the valence electron question. However, how do I calculate the concentration of the ions if the molecules do dissociate given the concentration of the compound. For example, CaCl2.

Well than Ca would be the same concentration as the original CaCl2 and Cl would have twice the concentration as Ca.