EMPIRICAL FORMULA

Ch 3 Exercise 6

EMPIRICAL FORMULA1. 1.72 g of the oxide of metal M contains 0.8 g of oxygen. Find the empirical formula of the oxide.

[Relative atomic mass of O = 16; M = 46]

2. 0.30 mol of element T combines with 14.4 g of oxygen to form oxide T. Determine the empirical formula of oxide T.[Relative atomic mass of O = 16]

3. In an experiment, 2.8 g of iron combined with 3.55 g of chlorine. What is the empirical formula of the compound formed?

[Relative atomic mass of Fe = 56; Cl = 35.5]

4. A hydrocarbon gas contains 80.0% carbon and 20.0% hydrogen by weight. (a) What is the empirical formula of the hydrocarbon?

(b) If the molecular mass of the hydrocarbon is 30, what is its molecular formula?

[Relative atomic mass of C = 12; H = 1]

5. When 3.20 g of the oxide of metal Y is reduced, 2.24 g of metal Y is formed. Determine the empirical formula of oxide Y.

[Relative atomic mass of Y = 56; O = 16]

6. A compound contains 15.23 g of sodium, 52.98 g of bromine and 31.79 g of oxygen. Calculate the empirical formula of the compound.[Relative atomic mass of Na = 23; O = 16; Br = 80]

7. A hydrocarbon compound contain 88.9% of carbon by weight. Determine the empirical formula of this compound.[Relative atomic mass of C = 12; H = 1]

8. 0.09 g of element Q combines with 0.08 g of element T to form a compound with empirical formula Q2T3. (a) What is the relative atomic mass of element Q?(b) What is the mass of Q that can be extracted from 51 g of Q2T3?[Relative atomic mass of T = 16]

Answers1. M2O52. TO3 3. FeCl2 4. CH3; C2H65. Y2O36. NaBrO3 7. C2H3 8. 27; 27 g9. The following are two methods to determine the empirical formula of metal oxides in the laboratory.

Method I: Reaction between the metal and oxygen in air

Method II: Reaction between the metal oxide and hydrogen

A student chose Method I to determine the empirical formula of the oxide of a metal M. The following data was obtained after the experiment.

Mass of crucible and crucible lid

= 41.30 g

Mass of crucible and crucible lid + metal M

= 43.10 g

Mass of crucible and crucible lid + oxide of metal M= 44.30 g

(a) Draw a diagram to show the set up of the experiment.(b) Determine the empirical formula of the oxide of metal M.

[Relative atomic mass of M = 24; O = 16]

(c) Write the chemical equation for the reaction.

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(d) What was observed during the experiment?

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(e) Predict what would have happened if the student forgot to cover the crucible.

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(f) How did the student ensure that the reaction was complete?

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(g) (i) If the student had chosen Method II to determine the empirical formula of magnesium oxide, predict what will happen.

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(ii) Explain your answer in (i).

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(h) Choose the most suitable method to determine the empirical formula of stanum(II) oxide.

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