4.1. Atoms http://www.ck12.org
that forms from the combination of carbon and oxygen is called carbon monoxide. Every sample of carbon monoxide
contains 16.0 g of oxygen for every 12.0 g of carbon, which simplifies to an oxygen/carbon mass ratio of 1.33 to 1.
In other words, a given mass of carbon needs to combine with exactly twice as much oxygen to make carbon dioxide
as it would to produce carbon monoxide. The figure below (Figure4.3) illustrates thelaw of multiple proportions.
Whenever the same two elements form more than one compound, the different masses of one element that combine
with the same mass of the other element are in the ratio of small whole numbers.
FIGURE 4.3
Carbon monoxide, on the left, contains
1.333 g of oxygen for every 1 g of carbon.
Carbon dioxide, on the right, contains
2.666 g of oxygen for every gram of car-
bon. The ratio of oxygen in these two
compounds is 1:2, which is a ratio of small
whole numbers.Sample Problem 4.1: Calculating Mass Ratios
Copper reacts with chlorine to form two compounds. Compound A contains 4.08 g of copper for every 2.28 g of
chlorine. Compound B contains 7.53 g of copper for every 8.40 g of chlorine. What is the lowest whole number
mass ratio of copper that combines with a given mass of chlorine?
Step 1: List the known quantities and plan the problem.
Known
- Compound A = 4.08 g Cu and 2.28 g Cl
- Compound B = 7.53 g Cu and 8.40 g Cl
Apply the law of multiple proportions to the two compounds. For each compound, find the grams of copper that
combine with 1.00 g of chlorine by dividing the mass of copper by the mass of chlorine. Then, find the ratio of the
masses of copper in the two compounds by dividing the larger value by the smaller value.
Step 2: Calculate.