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A 1.50 g sample of an unknown alkali metal carbonate was dissolved in water, and 31.10 mL of 0.350 M CaCl₂ was required to precipiate all the carbonate ions as CaCO₃. What is the name and formula of the unknown compound?

User Irriss
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Answer : The formula of unknown compound is
K_2CO_3 and the name of the compound is potassium carbonate.

Explanation :

First we have to calculate the moles of
CaCl_2


\text{Moles of }CaCl_2=\text{Concentration of }CaCl_2* \text{Volume of solution}=0.350M* 0.0311L=0.0109mole

Now we have to calculate the moles of unknown alkali metal carbonate.

Let the alkali metal be, 'M'.

The balanced chemical reaction will be:


M_2CO_3+CaCl_2\rightarrow CaCO_3+2MCl

From the balanced reaction we conclude that,

As, 1 moles of
CaCl_2 react with 1 mole of
M_2CO_3

So, 0.0109 moles of
CaCl_2 react with 0.0109 mole of
M_2CO_3

Now we have to calculate the molar mass of unknown alkali metal carbonate.


\text{Molar mass of }M_2CO_3=\frac{\text{Given mass of }M_2CO_3}{\text{Moles of }M_2CO_3}


\text{Molar mass of }M_2CO_3=(1.50g)/(0.0109mole)=137.6g/mole

Thus, the molar mass of
M_2CO_3 is 137.6 g/mole

Now we have to calculate the mass of alkali metal.


137.6=(2* \text{Mass of alkali metal})+(12)+(3* 16)


\text{Mass of alkali metal}=38.8g

Thus, we conclude that the alkali metal will be potassium (K) that has 38.8 grams of mass.

So, the formula of unknown compound is
K_2CO_3 and the name of the compound is potassium carbonate.

User Hindmost
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