3. a. The thermal decomposition of 2.076 g of Mgso, H2O produces 1.812 g of a pr

Question

3. a. The thermal decomposition of 2.076 g of Mgso, H2O produces 1.812 g of a product in a well-behaved reaction. There are two possibilities: MgSos.HO(sMgSOg(s) + H-0g) +MgO(s) SO3(g) + H2O(g) MgS04-H20(s) + Complete the following table, and then identify the correct solid product by comparing the calculated masses of MgSO4 and MgO with the observed mass of the product. Formula Weight Moles Mass (g) Substance MgSO. H2O 2.076g MgSO4 MgO Because the observed mass of the product is 1.812 g, the product is b. What qualitative test could be used to substantiate this result?

Explanation / Answer

a)substance formula weight moles mass

MgSO4.H2O 138 2.076/138= 0.0150 2.076g

MgSO4 120 1.812 /120= 0.015 1.812 g

MgO 40 1.812 /40 = 0.0453 1.812g

From the given equations

one mole of MgSO4.H2O can give only one mole of MgSO4 or one mole of MgO by either pathway.

As the mass produced shows (1:1) mole ratio of MgSO4 and (1:3) mole ratio for MgO.

We can conclude that the product is MgSO4 NOT MgO.

Because the mass is 1.812 g , it is Mgso4 not MgO.

b) Along with MgSO4 only water vapour is produced which does not change litmus color.

If it were MgO and SO3 gas , SO3 is an acidic oxide, that changes blue litmus to red.

SO by exposing the gases produced to moist blue litmus, we can confirm the product is MgSO4 and water.

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