Question

6\. Explain how the law of definite proportions applies to compounds.

Short answer

The Law of Definite Proportions states that a chemical compound always consists of the same proportions by mass of its elements, regardless of its source or method of preparation. In the case of water (H₂O), for example, the mass percentage of hydrogen is approximately 11.11%, while for oxygen it is approximately 88.89%. This consistent proportion of elements in water confirms the Law of Definite Proportions.

Step-by-step solution

Define the Law of Definite Proportions

The Law of Definite Proportions states that a chemical compound, regardless of its source, purity, or method of preparation, will always consist of the same proportions by mass of its elements.

Choose a chemical compound as an example

Let's use water (H₂O) as an example. Water is a compound that consists of two hydrogen atoms and one oxygen atom.

Calculate the proportions of elements in the compound

To find the proportion of elements in the compound, we need to know the relative atomic mass of each element. Hydrogen has a relative atomic mass of approximately 1 amu (atomic mass unit), and oxygen has a relative atomic mass of approximately 16 amu. For one molecule of water (H₂O): - The mass of two hydrogen atoms is: \(2 \times 1 \,amu = 2 \,amu\) - The mass of one oxygen atom is: \(1 \times 16 \,amu = 16 \,amu\) - The total mass of one molecule of water is: \(2 \,amu + 16 \,amu = 18 \,amu\) Now, let's calculate the mass percentage of each element in water: - Hydrogen: \(\frac{2 \,amu}{18 \,amu} \times 100\% \approx 11.11\%\) - Oxygen: \(\frac{16 \,amu}{18 \,amu} \times 100\% \approx 88.89\%\) No matter the source or method of preparation, water will always have the same mass proportions of hydrogen and oxygen.

Conclusion

This example demonstrates the Law of Definite Proportions, stating that a compound, such as water, will always have the exact same proportions by mass of its constituent elements, regardless of the source or method of preparation.

Key concepts

Chemical Compounds

When we talk about chemical compounds, we are referring to substances that are formed when two or more chemical elements are bonded together. This bonding results in a substance that has chemical properties different from the individual elements that comprise it. Every compound has a specific chemical formula that tells us the ratio of the elements present.

For example, water is a chemical compound composed of hydrogen and oxygen in a 2:1 ratio, represented by the formula H₂O. This fixed composition is a hallmark of the Law of Definite Proportions, which states that this ratio will remain constant regardless of the origin of the water, ensuring consistency in the properties and reactions of the compound across different samples.

• Compounds are pure substances.
• They have distinct boiling and melting points.
• Their properties differ from the elements they contain.

Understanding chemical compounds allows scientists to predict behaviors and interactions in various chemical processes.

Atomic Mass

Atomic mass plays a crucial role in understanding chemical compounds and their formation. It is the mass of an atom, typically expressed in atomic mass units (amu). The atomic mass of an element is a weighted average of the masses of its isotopes.

For example, hydrogen has an atomic mass of approximately 1 amu, and oxygen's atomic mass is about 16 amu. These values are essential in calculating the mass of compounds; for instance, in water (H₂O), we use the atomic masses of hydrogen and oxygen to determine the molecular mass of the compound. This understanding aids chemists in quantifying elements and predicting the mass proportions in compounds.

• Atomic mass is crucial for calculating the molar mass of compounds.
• Helps in stoichiometric calculations in chemical equations.
• Used to determine the mass percentage of elements in compounds.

Knowing the atomic mass allows for accurate predictions of how much of each element is needed or will result from a reaction.

Mass Percentage

Mass percentage is a useful way to express the concentration of an element within a compound. It tells us the proportion by mass of each element in a compound relative to the total molecular mass. Mass percentage is calculated using the formula: \(\text{Mass percentage} = \frac{\text{mass of element}}{\text{total mass of compound}} \times 100\%\).

In the case of water, the mass percentage of hydrogen is approximately 11.11%, while that of oxygen is about 88.89%. These percentages demonstrate the consistent composition of water, adhering to the Law of Definite Proportions. No matter where or how water is produced, the mass percentage of its elements remains constant.

• Mass percentage is useful in analytical chemistry.
• It helps in determining the empirical formula of compounds.
• Aids in quality control and verifying purity of substances.

This reliable ratio is key to understanding the composition of chemical substances.

Hydrogen and Oxygen

Hydrogen and oxygen are the two chemical elements that make up water, one of the most well-known chemical compounds. They exemplify how elements combine to form compounds with entirely new properties.

Hydrogen, with an atomic mass of about 1 amu, is the lightest element and is prevalent in a variety of compounds, from water to organic molecules. Oxygen, with an atomic mass of about 16 amu, is essential for life processes like respiration and is a key component of many substances.

• Hydrogen is flammable while oxygen supports combustion.
• When combined in water, they extinguish fires instead.
• Both elements are abundant and crucial in different fields of science.

These attributes highlight the importance of hydrogen and oxygen not only in water but across various chemical and biological contexts, illustrating how different ratios and bonding conditions lead to diverse substances.

Chemical Elements

Chemical elements are the building blocks of matter, distinguished by their unique atomic number, which represents the number of protons in their nucleus. Elements like hydrogen and oxygen are fundamental in forming compounds with new properties and uses.

Each element has specific properties, such as atomic mass, electronegativity, and electron configuration, which influence how it interacts with other elements. These interactions form compounds that are essential for numerous applications, from industrial processes to biological functions.

• Elements are listed in the periodic table based on their properties.
• They form chemical bonds to create compounds.
• Knowing the properties of elements helps in predicting chemical behavior.

Understanding chemical elements allows chemists to manipulate these fundamental building blocks of matter to innovate and develop new materials and processes.