# chemistry help

A solution of a metal carbonate, M2CO3, was prepared by dissolving 7.46 g of the anhydrous solid in water to give
1000 cm3
of solution. 25.0 cm3
of this solution reacted with 27.0 cm3
of 0.100 mol dm-3 hydrochloric acid.
Calculate the relative formula mass of M2CO3 and hence the relative atomic mass of the metal M

how do you know the molar ratio is 2??
Original post by miac0328
A solution of a metal carbonate, M2CO3, was prepared by dissolving 7.46 g of the anhydrous solid in water to give
1000 cm3
of solution. 25.0 cm3
of this solution reacted with 27.0 cm3
of 0.100 mol dm-3 hydrochloric acid.
Calculate the relative formula mass of M2CO3 and hence the relative atomic mass of the metal M

how do you know the molar ratio is 2??

hydrochloric acid has only one acidic hydrogen atom that provides hydrogen ions in solution.

H+(aq) comes from HCl(aq)

These react with carbonate ions to make carbon dioxide and water, CO2 + H2O.

But to make water you need two hydrogen atoms, so you must use two mol of HCl per mol of carbonate.

2H+(aq) + CO32- --> CO2 + H2O.

All acids react with carbonates in this way (although it is actually a two stage reaction, but that's for another day)
(edited 3 months ago)
thanks,
so does that mean that any metal carbonate + acid the ratio will always be 1:2?
Original post by miac0328
thanks,
so does that mean that any metal carbonate + acid the ratio will always be 1:2?

No. If the acid is dibasic it will be 1:1.