Pre -lab Assignment ? I. Explain why the formula for hydrogen peroxide (H2O2) is

Question

Pre -lab Assignment ? I. Explain why the formula for hydrogen peroxide (H2O2) is not the empirical formula. 2. Why must the crucible be allowed to cool to room temperature before an accurate mass reading can be obtained? 3. Can you determine the molecular formula of a substance from its percent composition? Explain your answer. 4. A substance was found to have contained 65.95% barium and 34.05% chlorine upon analysis. What is the empirical formula of the compound? 5. An oxide of mercury will thermally decompose when heated. A 0.204 g sample of the mercury oxide is heated to form 0.189 g of mercury. What is the empirical formula of the mercury oxide?

Explanation / Answer

1)

Empirical formula must be divided by the common denominator, in this case 2 is common, then:

OH or HO should be the 3emperical formula

2)

The cruicible must be at room tmeprature since it amy react. Besides, for safety reasons

3)

No, you can only identify its empricial formula, i.e. the ratio between its components, but you can't calculate the chemical formula

4)

Assume m = 100 then

m of Ba = 65.95

MW of Ba = 137.327

Mol = mass/MW = 65.95/137.327 = 0.48

for Cl --> 35 g

MW of Cl = 35

mol = 35/35 = 1

Ratio Ba --> 0.5 and Cl = 1

or

Ba1: 2Cl

Empirical formula BaCl2

5)

m = 0.204 of sample HgO

m = 0.189 g of Hg

MW of Hg = 200.59

mol = mass/MW = 0.189/200.59 = 9.4*10^-4

mol of O2 = mass/MW = (0.204 -0.189) / (16) = 9.375*10^-4

ratio:

9.4*10^-4 : 9.375*10^-4= 1.002

Empriical formula is HgO

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