quick CHEM QUESTION!! (1 Viewer)

[syera]

hey guys,
i was studying for my chemistry yearly exam, when i came across this question...

the potassium ion has the same configuration as:
a) the sodium ion
b) the neon atom
c) the magnesium atom
d) the sulfide ion

the answer is d) sulfide ion.
but i don't understand how to get that answer...

can anyone explain please?

 

[vizman]

what lourai*87 said

 

[priesty]

hmm strange...

K+ is more similar to Na+

perhaps theres another meaning to it? consult ur teacher! maybe its just and error on the answers sheet. Or u've read the answer sheet incorrectly

 

[syera]

hmmm i thought it was a) too... i put that on my exam (coz the question is from a topic test i did earlier this year) but i got it wrong!...
weird...
thanks neway!

 

[lourai*87]

Ok after some deliberation. d) is definately correct. I dont know if you've done Spectroscopic notation, but thats what i have done at uni and how i worked this out.

Potassium (K) atomic number 19 (ie. total 19 electrons).
Potassium ion (K⁺) - K loses 1 electron, so now total 18 electrons

Sulfur (S) atomic number 16 (ie total 16 electrons)
Sulfide ion (S^2-) - S gains 2 electrons, so now total 18 electrons

Now that i have written that, the notation is irrelevant. They have the same number of electrons so therefore have the same electronic configuration.

EDIT: just a note, the reason you are thinking it was Na⁺ is i presume because they are in the same group. Elements in the same group have similar properties but not the same configurations because as you go down the group each element has more electrons. Hope all this helps

 

[kloudsurfer]

Ok after some deliberation. d) is definately correct. I dont know if you've done Spectroscopic notation, but thats what i have done at uni and how i worked this out.

Potassium (K) atomic number 19 (ie. total 19 electrons).
Potassium ion (K⁺) - K loses 1 electron, so now total 18 electrons

Sulfur (S) atomic number 16 (ie total 16 electrons)
Sulfide ion (S²⁺) - S gains 2 electrons, so now total 18 electrons

Now that i have written that, the notation is irrelevant. They have the same number of electrons so therefore have the same electronic configuration.

EDIT: just a note, the reason you are thinking it was Na⁺ is i presume because they are in the same group. Elements in the same group have similar properties but not the same configurations because as you go down the group each element has more electrons. Hope all this helps

Shouldnt it read
'Sulfide ion (S2-)' instead of sulfide ion '(S2+)?'

And yeah, what she said.

 

[Riviet]

Shouldnt it read
'Sulfide ion (S2-)' instead of sulfide ion '(S2+)?'

That's correct, just to clarify:
S + 2e^- -> S^2-

 

[Forbidden.]

Does the sulfide ion S^2- have 2 extra electrons or 2 less electrons ?

 

[csuwai]

Does the sulfide ion S^2- have 2 extra electrons or 2 less electrons ?

An sulfide ion does not have 2 extra electrons or 2 less electrons.. Ur thinkin abt sulfur as an element

 

[syera]

thanks guys!
i understand where i went wrong now thanx to ur explanation lourai*87... i did what u thought i did (i chose Na+ because it was in the same group)
i know not to do that again though!
=)

 

[Nakashima]

An sulfide ion does not have 2 extra electrons or 2 less electrons.. Ur thinkin abt sulfur as an element

2- indicates a gain of 2 electrons.

A sulfide ion has 2 more electrons (making 8 in total) than the sulfur atom (which has 6 electrons in its outer shell).

 

[lourai*87]

Youre right Kloudsurfer. I know what i meant to say.. typo i fixed it up in my post. Thnks

After thinking about it more. Both now have configuration 2.8.8 No need to go into silly spectroscopy and complicate everything

 

[syera]

okay... im studying moles now.. and they get kind of confusing at some parts...
i dont understand this question:
-- In the equation 2H2(g) + O2 --> 2H2O(l)
how many moles of oxygen are needed for the complete combustion of 1 mole of hydrogen?
how exactly do i work that out?

 

[lourai*87]

okay... im studying moles now.. and they get kind of confusing at some parts...
i dont understand this question:
-- In the equation 2H₂(g) + O₂ --> 2H₂O(l)
how many moles of oxygen are needed for the complete combustion of 1 mole of hydrogen?
how exactly do i work that out?

I hated moles so much!!! The reaction above is a combustion reaction -- ie reacting with Oxygen.. just incase it confused you (it used to confuse me anyway).
=p
If 2 moles of Hydrogen react woth 1 mole of Oxygen to produce 2 moles of water, then divide all by two, 1 mole Hydrogen reacts with 1/2 mole of Oxygen to produce 1 mole of water.

Seems too simple to be correct but im pretty sure it is

 

[syera]

thanks
putting it that way makes it sound so easy
i hate moles toooooo

ummm i got another question :S if u can help with that too...!
--- Copper occurs in nature as isotopes 29-Cu, and 65 Cu. What percentage of each isotope must be present if the relative mass for copper is 63.55?

 

[airie]

thanks
putting it that way makes it sound so easy
i hate moles toooooo

ummm i got another question :S if u can help with that too...!
--- Copper occurs in nature as isotopes 29-Cu, and 65 Cu. What percentage of each isotope must be present if the relative mass for copper is 63.55?

Let the percentage of 29-Cu be x,
then 29*x + 65*(1-x) = 63.55,
which gives x being approx. 4%.

But are you sure there are isotopes of copper with atomic mass 29? I mean, that's its atomic number...so there aren't any neutrons in those atoms. How weird. o.0

 

[syera]

i dunno... i'll check the question to make sure after
but i dont get that question at alll.

 

[syera]

I hated moles so much!!! The reaction above is a combustion reaction -- ie reacting with Oxygen.. just incase it confused you (it used to confuse me anyway).
=p
If 2 moles of Hydrogen react woth 1 mole of Oxygen to produce 2 moles of water, then divide all by two, 1 mole Hydrogen reacts with 1/2 mole of Oxygen to produce 1 mole of water.

Seems too simple to be correct but im pretty sure it is

okay so for this question: in the equation CaCo3 --> CaO + CO2
how many moles of calcium oxide are produced from 2 moles of calucium carbonate? SOO, instead of dividing, I multiply two by one and 2 moles of calcium oxide are produced rite?

and related to that question, what mass in grams of calcium oxide is produced from 50g of calcium carbonate?

 

[lourai*87]

okay so for this question: in the equation CaCo3 --> CaO + CO2
how many moles of calcium oxide are produced from 2 moles of calucium carbonate? SOO, instead of dividing, I multiply two by one and 2 moles of calcium oxide are produced rite?

and related to that question, what mass in grams of calcium oxide is produced from 50g of calcium carbonate?

Yes..thats right! as for the second part, i'll sit and work that one out later and then try to explain it somehow.

There is some way of working out that copper question, but i can never work it out sorry.

 

[lourai*87]

Ok i think i can do this.

You are familiar with the fact that the number of moles = mass (of substance) / mole weight ? that is, n=m/mw ?

Also, since the ratio of CaCO₃:CaO:CO₂ is 1:1:1 (does that make sense? It is because there is an 'imaginary 1' in front of each).

Now, you should also know that you cant convert straight from mass A to mass B, or from moles A to moles B.

I drew a pretty picture =p Sometimes it helps to look at it.

Right, so having said all of that, maybe you could have a go at working it out? Might help you a little more than me just doing the working out.. this way you can go through the process.... let me know what you got and how you did it =) And if youre still partly lost, then ill help you some more