Problem 12 - Chemistry: The Central Science in SI Units, Global Edition

Question

Sodium reacts with oxygen in air to form two compounds: sodium oxide and sodium peroxide. In forming sodium oxide, \(23.0 \mathrm{~g}\) of sodium combines with \(8.0 \mathrm{~g}\) of hydrogen. In forming sodium peroxide, \(23.0 \mathrm{~g}\) of sodium combines with \(16.0 \mathrm{~g}\) of oxygen. (a) What are the mass ratios of oxygen in the two compounds? (b) What fundamental law does this experiment demonstrate?

Step-by-Step Solution

Answer

a) The mass ratios of oxygen in sodium oxide and sodium peroxide are \(\frac{8}{31}\) and \(\frac{16}{39}\), respectively. b) The fundamental law this experiment demonstrates is the Law of Multiple Proportions.

Step 1: Mass ratio of oxygen in sodium oxide

We are given that the mass of sodium is \(23.0 \mathrm{~g}\) and the mass of oxygen is \(8.0\mathrm{~g}\). The mass ratio of oxygen in sodium oxide is calculated as follows: Mass Ratio of Oxygen in Sodium Oxide (NaO) = \(\frac{\text{Mass of Oxygen}}{\text{Mass of Sodium + Mass of Oxygen}}\) Mass Ratio of Oxygen (NaO) = \(\frac{8}{23 + 8}\) = \(\frac{8}{31}\)

Step 2: Mass ratio of oxygen in sodium peroxide

Similarly, the mass of sodium is \(23.0 \mathrm{~g}\) and the mass of oxygen is \(16.0\mathrm{~g}\). The mass ratio of oxygen in sodium peroxide is calculated as follows: Mass Ratio of Oxygen in Sodium Peroxide (NaO2) = \(\frac{\text{Mass of Oxygen}}{\text{Mass of Sodium + Mass of Oxygen}}\) Mass Ratio of Oxygen (NaO2) = \(\frac{16}{23 + 16}\) = \(\frac{16}{39}\) Thus, the mass ratios of oxygen in sodium oxide and sodium peroxide are \(\frac{8}{31}\) and \(\frac{16}{39}\), respectively. Step 2: Identify the fundamental law this experiment demonstrates

Step 3: Fundamental law demonstrated

The mass ratios of oxygen in the two compounds of sodium show that the mass of oxygen that combines with a fixed mass of sodium is in a simple whole number ratio (1:2). This experiment demonstrates the fundamental law known as the Law of Multiple Proportions. In summary, a) The mass ratios of oxygen in sodium oxide and sodium peroxide are \(\frac{8}{31}\) and \(\frac{16}{39}\), respectively. b) The fundamental law this experiment demonstrates is the Law of Multiple Proportions.

Key Concepts

Chemical Reactions

Chemical reactions are processes where substances known as reactants transform into new substances called products. In the context of sodium compounds reacting with oxygen, sodium undergoes a chemical change to form different types of oxide. This involves breaking bonds in the sodium and oxygen molecules, and forming new bonds in sodium oxide and sodium peroxide. Each compound has distinct properties, reflecting the new chemical structures formed.
Sodium oxide and sodium peroxide form as products, showcasing how the same element can react in different ways under diverse conditions. Here, the difference lies in the amount of oxygen that combines with sodium, leading to two distinct chemical reactions.
Understanding chemical reactions helps explain how elements interact to form a wide variety of compounds, which is a foundation of chemistry.

Mass Ratios

Mass ratios in a compound express the proportion of each element in the compound in terms of mass. They are fundamental in understanding the composition of compounds. For sodium oxide and sodium peroxide, the ratios of oxygen to sodium are \(\frac{8}{31}\) and \(\frac{16}{39}\), respectively.
These ratios reveal how much of oxygen combines with a fixed amount of sodium.
This helps us understand the different ways sodium and oxygen can combine to form various compounds.
The mass ratio is calculated by taking the mass of an element and dividing it by the total mass of the compound. These ratios often help in identifying laws like the Law of Multiple Proportions, where elements combine in simple whole number ratios.

Sodium Compounds

Sodium compounds are chemical compounds containing the element sodium, well-known for its reactivity and presence in many forms around us. The two sodium compounds discussed in this context are sodium oxide (\(\text{Na}_2\text{O}\)) and sodium peroxide (\(\text{Na}_2\text{O}_2\)).
Each compound has unique chemical and physical properties since they contain different amounts of oxygen in their formula. Sodium oxide is usually formed when sodium burns in a limited supply of oxygen, producing a white powder useful in ceramics and the glass industry. Sodium peroxide, containing more oxygen, is produced under more abundant oxygen conditions and is often used as a bleaching agent and in oxygen generation.
Sodium's versatility in forming various compounds highlights the vast array of chemical reactions possible with even a single element.