A sample of a pure iron oxide synthesized in a laboratory contains 5.60\text{ g} of iron a… — JAMB UTME

A sample of a pure iron oxide synthesized in a laboratory contains $5.60\text{ g}$ of iron and $2.40\text{ g}$ of oxygen. According to the Law of Definite Proportions, what is the mass of iron, in grams, present in a $20.0\text{ g}$ sample of the same iron oxide collected from a natural deposit?

Answer: 14 g

Answer

The mass of iron present in the 20.0 g sample of iron oxide is 14.0 g.

According to the Law of Definite Proportions, a pure chemical compound always contains the same elements combined together in the exact same proportion by mass, regardless of its source or method of preparation. In the laboratory sample,

8.00\text{ g}

of iron oxide contains

5.60\text{ g}

of iron, giving an iron mass composition of

70\%

. Therefore, a

20.0\text{ g}

natural sample of the same compound must also contain

70\%

iron by mass, which equals

14.0\text{ g}

Step-by-Step Solution

Calculate total mass of the laboratory sample

5.60\text{ g} + 2.40\text{ g} = 8.00\text{ g}

The total mass of the compound is the sum of the constituent element masses (Law of Conservation of Mass).

Find the mass percentage/fraction of iron

\frac{5.60\text{ g}}{8.00\text{ g}} = 0.70

(or

70\%

)

By the Law of Definite Proportions, the mass ratio of elements in a pure compound is constant.

Calculate mass of iron in the 20.0 g natural sample

0.70 \times 20.0\text{ g} = 14.0\text{ g}

Applying the constant mass composition percentage to the new sample mass.

Key Concept

Law of Definite Proportions (Constant Composition)

Estimated Time:1m 30s

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