Chemistry?!?

[Luwayla]

A mixture of magnesium bromide and magnesium carbonate is known to contain 3 mol of magnesium ions and 4 mol of bromide ions.

How many moles of carbonate ions are present?

A 1
B 2
C 3
D 4

Please show all working, so I can learn.

[ziggle]

Magnesium Carbonate: MgCO3
Magnesium Bromide: MgBr2

Assume you mixed m moles of MgCO3 and n moles of MgBr2.

#Bromine moles = 2*n = 4 -> n =2
# Mg moles = m+n = 3 -> m =1
#Carbonate moles = m = 1

The answer is (A), 1

1 mole of MgCO3 + 2 moles of MgBr2 will make a solution with

3 moles of Mg, 4 moles of Br, and 1 mole of carbonate

[Vinny L]

Magnesium bromide is MgBr2 and Magnesium carbonate is MgCO3. If they are saying that there are 3 moles of Mg and 4 moles of bromide that means that there are two moles of MgBr2 because multiply MgBr2 by 2 is the only way to get 4 moles of Br2. Therefore since MgCO3 is unchanged, there is one mole of carbonate ions.

[gladys]

First write the formulae for the compunds:

MgBr2 and MgCO3

If there are 4 moles of bromide, then there must be 2 moles of MgBr2 present.

Thus from MgBr2 you have 2 moles of the Mg. All together there are 3 moles of Mg so there must be one mole of Mg from MgCO3.

Since 1 mole of MgCO3 contains 1 mole of carbonate, there is 1 mole of carbonate ions present.

Answer is A