Chapter 3: Problem 9

State the law of definite proportions.

Short Answer

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The Law of Definite Proportions states that a given chemical compound always contains its component elements in a fixed ratio (by mass) and does not depend on its source or method of preparation. For example, the mass ratio of Hydrogen to Oxygen in water will always be 1:8, irrespective of the source of the sample.

Step by step solution

Definition

The Law of Definite Proportions states that a given chemical compound always contains its component elements in a fixed ratio (by mass) and does not depend on its source or method of preparation.

Understanding the basic principle

This law basically means that, for example, water \(H_2O\) will always consist of hydrogen and oxygen in a 2:1 ratio by mass. No matter where the water comes from - from a river, from a laboratory, or from a comet zooming through space - the proportions of hydrogen to oxygen in water are always the same.

Providing an example

Let's take the case of water. The atomic mass of Hydrogen (\(H\)) is 1 and Oxygen (\(O\)) is 16. So, in \(H_2O\) (water), the proportion by mass will always be \( \frac{2*1}{16} = \frac{1}{8} \). That means, in a sample of water, the mass ratio of Hydrogen to Oxygen will always be 1:8, irrespective of the source of the sample.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Chemical Composition

Understanding the chemical composition of a substance is fundamental in chemistry. It refers to the identity and quantity of the elements that make up a chemical compound. For instance, water (H_2O) is composed of hydrogen and oxygen. Here, the subscript '2' indicates that two atoms of hydrogen combine with one atom of oxygen.

Identifying the chemical composition allows us to understand the properties of different substances and predict how they will react with others. It's similar to knowing the ingredients in a recipe; each component contributes to the overall characteristics of a dish.

Fixed Ratio by Mass

The concept of a fixed ratio by mass is a key part of understanding compounds. It means that the masses of the elements in a compound are always in the same proportions, no matter the size or source of the sample. To visualize this, consider baking cookies with a recipe that you scale up or down. No matter how many cookies you bake, the proportion of flour to sugar remains constant if you're using the same recipe.

For a chemical compound, this scaling up or down can be seen in the combination of atoms. The ratio by mass is determined by the atomic mass of each element and the number of atoms present, maintaining consistency across all samples of the compound.

Chemical Compound

A chemical compound is a substance formed when two or more elements are chemically bonded together. The properties of a compound differ significantly from those of its individual elements. Salt, for example, is a compound made from sodium (a metal that reacts violently with water) and chlorine (a poisonous gas). Together, as sodium chloride (NaCl), they form an edible crystal that enhances the flavor of food.

The stability and unique characteristics of chemical compounds are due to the specific ways in which atoms bond, through ionic or covalent bonds, and form molecules or crystalline structures, giving compounds their distinct properties.

Atomic Mass

The term atomic mass refers to the mass of a single atom, most often expressed in atomic mass units (amu). Each element’s atomic mass is roughly equivalent to the sum of the masses of its protons and neutrons. Since electrons have a negligible mass, they are not included in this calculation.

Atomic mass allows chemists to weigh and quantify atoms, despite their minuscule size. For instance, hydrogen (H), the lightest element, has an atomic mass of approximately 1 amu, while oxygen (O) is about 16 amu. This metric is crucial for determining the proportions in which different elements combine to form compounds, as highlighted by the law of definite proportions.

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State the law of definite proportions.

Short Answer

Step by step solution

Definition

Understanding the basic principle

Providing an example

Key Concepts

Chemical Composition

Fixed Ratio by Mass

Chemical Compound

Atomic Mass

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