me again!!!!!!

a fossilised bone weighing 2.50g required 28.0g of 1.5 mol dm^-3 hydrochloric acid to react with all of the calcium carbonate it contained. what is the percentage of calcium carbonate in this bone??
i ve started it by doing the equation...

CaCO3 + 2HCl ----->  CaCl2 + H2O + CO2

then i calculated the relative molecular mass of hydrochloric acid which is 36.5, and the next thing we know is that the amount in moles was 1.5, so i said in 28.0g there are 0.767mol, which i am not sure if i did good.... then the next thing i know is that the ratio is 1:2...what do i do?

28.0g of 1.5 mol dm^-3 hydrochloric acid

There was 28.0 g of 1.5M solution. To calculate amount of acid you have to know its volume. This in turns mean you need density.

Either assume density of 1g/mL, or use density tables - although it ill be not easy, as they contain only information about densities vs percent concentrations... Well then, use density 1.0246g/mL. If you will be asked about source of this information you may say "Borek told me" if you dare

i really need to understand chemistry in general my friend not only molarity....