gCHEM Q....pretty lost.

[illbirz]

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What are the oxidation numbers of CaH2? A. Ca +2, H2 -1
B. Ca +1, H2 -1
C. Ca +2, H2 -2
D. Ca -2, H2 +2
E. Ca -1, H2 +1






How is A the answer and not C. I guessed the answer as C simply because it seemed like the only thing closest to the actual thing.

 

[klutzy1987]

The answer is A. The way you would do this is to look at the known oxidation numbers and then calculate the unknown. Since Ca is a group 2 metal its oxidation is always going to be +2. Once you know that Ca is +2 then 2 hydrogens together have to equal to -2 in order to make the overall reaction nuetral. therefore each hydrogen must be equal to -1 which is represented by choice A (Ca2+ H1-)

 

[illbirz]

Oh i just thought, that it meant H2 is -1. I didnt know they meant that each H has a negative 1 charge on it.


Thanks. 👍

 

[hoss19]

The answer is A. The way you would do this is to look at the known oxidation numbers and then calculate the unknown. Since Ca is a group 2 metal its oxidation is always going to be +2. Once you know that Ca is +2 then 2 hydrogens together have to equal to -2 in order to make the overall reaction nuetral. therefore each hydrogen must be equal to -1 which is represented by choice A (Ca2+ H1-)

i think there is a type in the the answer choices, they say that H2 has a cumulative charge of -1 (A), but that is not correct. Each H has a -1 charge, making H2 a -2 charge overall. Choice C is the right one in my book.

 

[doc toothache]

i think there is a type in the the answer choices, they say that H2 has a cumulative charge of -1 (A), but that is not correct. Each H has a -1 charge, making H2 a -2 charge overall. Choice C is the right one in my book.

Strictly speaking you are correct. In this case, however, they probably used the H2 to signify the generic hydrogen rather than to indicate that there were two hydrogens with a total charge of -1, -2, +1 or +2. The proper designation should have been H-1, H-2. H+1 or H+2.

 

[klutzy1987]

i think there is a type in the the answer choices, they say that H2 has a cumulative charge of -1 (A), but that is not correct. Each H has a -1 charge, making H2 a -2 charge overall. Choice C is the right one in my book.

It is possible that there is a typo in the answer choices however the charge on each hydrogen is going to be -1. Together they obviously equal -2. Depending on what the question asked that would be the answer.