Need quick answer! Due tomorrow... Dry mass for Chemistry lab?

Question

How do you find dry mass? We are doing a lab of “gravimetric analysis of a metal carbonate” and one of the pre lab questions is to find the dry mass. The M stands for the mystery element we need to find.
The reaction is CaCl2(aq) + M2CO3(aq) —> CaCO3(s) + 2MCl(aq)My friend and I found that the mass of M2CO3 is 2.13g in this experiment, and the mass of CaCO3 is 1.838g. The question being asked is “calculate the dry mass of M2CO3 used”
How do you find dry mass? We also have other measurements I didn’t list here... if those are needed please tell me

Bobby · Accepted Answer

A known amount of the soluble unknown carbonate is dissolved in water to dissociate the compound into ions
M2CO3(s) = 2M+ (aq) + CO3 2- (aq) 
When a solution of calcium chloride, CaCl2, is added to this metal carbonate solution, a precipitate of calcium carbonate forms
 Ca 2+ (aq) + CO3 2- (aq) = CaCO3(s) 
The overall reaction represents a double-displacement reaction with a precipitate formed
CaCl2(aq) + M2CO3(aq) =CaCO3(s) + 2MCl(aq)
The precipitated calcium carbonate is then filtered, dried, and weighed. 
The molar mass of the alkali metal carbonate can be determined using stoichiometry

mass of CaCO3 is 1.838g
moles of CaCO3 = 1.838g / 100.0 g/ mol = 0.01838 moles
from the nett equation we see the moles of M2CO3 = 0.01838
these moles have a mass of 2.13g so molar mass of M2CO3 = 2.13g / 0.01838 mole
= 115.9 g / mol
the CO3 contributes 60 g to the molar mass so mass of M2 = 55.9 g
mass of M in the molar mass of M2CO3 = 27.9 g 
M looks like Si molar mass 28,0 
compound looks like SiCO3 >>>> this is the purpose of the experiment

the dried mass of M2CO3 the mass quoted  2.13g. 
Heating in the oven before addition to the solution ensures an accurate mass for your stoichiometric calculations.

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Need quick answer! Due tomorrow... Dry mass for Chemistry lab?

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