Calculate the relative molecular mass of X2CO3?

Question

25cm3 of a solution containing 1.86g of a metal carbonate, X2CO3, in 250cm3 exactly reacted 27cm3 of 0.100 mol dm3 hydrochoric acid. Calculate the RMM of the X2CO3.

X2CO3 + 2HCL ----> 2XCL + CO2 + H20

Answer 1

Two moles of HCl are rquired for every mole of X2CO3.

27 cm3 is 27/1000 dm3 = 0.027 dm3 of HCl

0.027 dm3 * 0.100 mol/dm3 = 0.0027 moles of HCl

This means that there were 0.0027/2 = 0.00135 moles of X2CO3

If 1.86 g of X2CO3 were in 250 cm3 of solution, then 25 cm3 would contain:

25 cm3/250 cm3 * 1.86 g = 0.186 grams of X2CO3.

From this we know that 0.00135 moles = 0.186 g

0.186g/0.00135 mol = 137.8 g/mole.

(by the way, this would mean that the atomic mass of the metal = 39 or so. The metal is Potassium).