Why is the "total charge" of Al(NO3)3 six?

Question

Chem question! The 3's are coefficients. I don't understand why the total charge of the molecule Al(NO3)3 would be six. If someone can explain this to me it'd be really helpful.

And also, can someone tell me what (a) the balanced equation would be for the reaction between Mg(OH)2 (base) and Vinegar (acetic acid)? And (b) determine the moles of vinegar per mole of Mg(OH)2? (the 2 is a coefficient)

Thanks SO much.

Answer 1

Total charge of 6 come from 3+ of Al3+ and 3- from three NO3-.

a) Mg(OH)2 + 2CH3COOH ---> Mg(CH3COO)2 + 2H2O
Note: Resulting product is Magnesium acetate Mg(CH3COO)2 not Magnesium acetic acid Mg(CH3COOH)2.

b) there are 2 moles of vinegar per mole Mg(OH)2

Answer 2

since the nitrate ion (NO3) has a charge of -1, there are 3 negative charges in the ion. to balance this, the aluminum ion must have a charge of +3. therefore, the total charge (positive plus negative) must be 6, since there are 3 positive and 3 negative charges.
a) Mg(OH)2 + 2CH3COOH -->2H2O +Mg(CH3COOH)2
b) there are 2 moles of vinegar per mole of Mg(OH)2