Understanding Hydrides of Group 5 and 6 for Chemistry Exam

[leena19]

Hello everyone,
this is a question I've asked at another chemistry forum,
and has been bothering me for awhile .
http://www.chemicalforums.com/index.php?topic=34742.0"

And ... the only only reason I'm posting it here aswell,is causeI have my chem exam on Thursday(the day after tomorrow) and...I'm the kinda idiot(also a blabbermouth) who can't skip a problem unless I'm absolutely sure I've understood it,so... I would really appreciate it if I could find a solution to this before my exams...


And oh...I know I ask a lot of stupid questions ,so if you think this is one of those,just tell me & i won't bother you guys.
(well,i might pester your'll with other questions,but no more pestering after my exams,for atleast a week,promise. :) )

thx.

 

[chemisttree]

You say that the acidity of the hydrides increases from top to bottom (from NH3 to AsH3) and that the reverse is seen if you go backwards from BiH3 to SbH3! Wouldn't the reverse also be seen if you go from AsH3 to NH3?

Sounds like someone is asking you a trick question...

 

[leena19]

THANK YOU VERY MUCH FOR REPLYING!

You say that the acidity of the hydrides increases from top to bottom (from NH3 to AsH3) and that the reverse is seen if you go backwards from BiH3 to SbH3! Wouldn't the reverse also be seen if you go from AsH3 to NH3?

Er...is that a trick question ?
Sorry if my problem isn't clear,but this is basically what my question is,

$$\stackrel{\leftarrow}{}$$
Arranged in increasing order of acid strength
AsH₃ > PH₃ > NH₃ > SbH₃ > BiH₃

The acidity increases from NH₃ to AsH₃,then the acidic strength decreases from SbH₃ to BiH₃ .
What makes the group5 hydrides react this way?

 

[chemisttree]

What is the oxidation state of Bi in the BiH₃ compound? What about BiH₂^-?

Acidity reaction would be:

BiH₃ <--------> BiH₂^- + H⁺

 

[leena19]

What is the oxidation state of Bi in the BiH₃ compound?

All group 5 hydrides are trivalent,so the oxidation state of Bi would be -3

What about BiH2-?

The same. -3 ?

Not sure how to proceed from here.

 

[chemisttree]

Is -3 a possible oxidation state for Bi?

http://periodic.lanl.gov/elements/83.html

 

[leena19]

Thanks for the very useful link.
Ok so the oxidation state of Bi in BiH₃ is +3 and in BiH₂^-,it is +1 .
Then,since it's a metal it has to be more basic(i.e less acidic) than SbH3.
But SbH3 and AsH3 are metalloids...?

Can you tell me what I should do next?

thx.