3. Explain how this is an example of the Law of Multiple Proportion: Two differe

Question

3. Explain how this is an example of the Law of Multiple Proportion:

Two different compounds formed from carbon and oxygen have the following mass ratios:

1.33 g O: 1 g C and 2.66 g O: 1 g C.

Calculate the atomic mass of gallium if gallium has 2 naturally occurring isotopes with the following masses and natural abundances:

                        Ga-69                            68.9256 amu                      60.11%

                        Ga-71                            70.9247 amu                      39.89%

                Silver has two naturally isotopes and has an atomic mass of 107.868 amu. One isotope is Ag-109 isotope (108.905 amu) and has a natural abundance of 48.16%. What is the mass in amu of the other isotope?

Explanation / Answer

Compound 1: The percentage of C in the compound = {1 g/(1+1.33) g}*100 = 42.9%

The percentage of O in the compound = 100 - 42.9 = 57.1%

Compound 2: The percentage of C in the compound = {1 g/(1+2.66) g}*100 = 27.3%

The percentage of O in the compound = 100 - 27.3 = 72.7%

Law of Multiple Proportion states that the masses of one element which combine with a fixed mass of the second element are in a ratio of whole numbers.

In the case of compound 1, there is 57.1/42.9 = 1.33 g O per g C.

In the case of compound 2, there is 72.7/27.3 = 2.66 g O per g C.

Dividing the mass O per g C of the second (larger value) compound by the first (smaller value) compound :

2.66 / 1.33 = 2

This means that the masses of oxygen that combine with carbon are in a 2:1 ratio. The whole number ratio is consistent with the Law of Multiple Proportions.

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