Asked by Smarth

An unknown element reacts with bromine to give bromide, MBr3. If 2.809g of the unknown element gives 27.765grams of MBr3, what is the element? ( give the symbol )


I don't understand the M in the MBr3...can someoen please help me with this question ASAP

thanks a lot
Answered by bobpursley
M means some metal, such as Mg, Cr, Al. Note the metal is +3 valence.

well, in the compound, it has 27.765grams, of which the metal is (27.765-2.809) grams, and the Br is 2.809 grams.

Now, this you have 2.809grams Br, so you have 2.809/AtomicwtBr moles of Br.

But in the formula, you have 1/3 this number of moles, or
molesM=1/3*2.809/atomicwtBr

Now the easy part.
massM=molesM/atomicmassM

solve for the atomicmassM
and you can ID the Metal on the periodic table. Remember it is group +3, or +13, or a multivalent metal that can have a +3 valence.
Answered by Smarth
"well, in the compound, it has 27.765grams, of which the metal is (27.765-2.809) grams, and the Br is 2.809 grams. " i don't understand this as you said br is 2.809 but the question says the unknown element is 2.809 grams?
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