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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: stevo312 on May 19, 2008, 11:42:01 AM

Title: HELP ASAP! OXIDATION NUMBERS QUESTION
Post by: stevo312 on May 19, 2008, 11:42:01 AM

3.6g of magnesium metal were added to an excess of solution of an arsenic compound containing Asⁿ⁺ and 7.5g of arsenic were deposited. what is the oxidation number of arsenic in the coumpound?
A. +2
B. +3
C. +4
D. +5

answer is +3 btw  but i need help to work it out

Title: Re: HELP ASAP! OXIDATION NUMBERS QUESTION
Post by: Borek on May 19, 2008, 12:40:04 PM

Please write balanced reaction equation.

Title: Re: HELP ASAP! OXIDATION NUMBERS QUESTION
Post by: stevo312 on May 20, 2008, 04:54:31 AM

there is no balanced equation, thats why i cant work it out

Title: Re: HELP ASAP! OXIDATION NUMBERS QUESTION
Post by: Borek on May 20, 2008, 05:15:29 AM

No no no, it is up to YOU to write this equation. Note: try to write it using not some number (like 2, 3, 4) but using n (like in Asⁿ⁺).

Title: Re: HELP ASAP! OXIDATION NUMBERS QUESTION
Post by: wilson on May 20, 2008, 06:14:49 AM

Yep, you can use A B C D to represent your stoichiometric coefficients. From there form a simple equation, to ensure that charges on both sides are balanced (this equation should contain n). And how to obtain the values of A B C D? Basic stoichiometry calculations from weight and molar mass.  :)