Question

How many hydrogen bonded water molecules are associated with \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\) ? (a) Five (b) One (c) Four (d) Three

Short answer

There are five hydrogen bonded water molecules associated with \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\).

Step-by-step solution

Identify the Substance

Start by carefully reading the chemical formula given. The formula is for Copper(II) sulfate pentahydrate, which is denoted by \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\). This substance is a hydrate, meaning it has water molecules associated with it within its crystal structure.

Understand the Hydrate Notation

The number directly following the hydrate notation (\(\cdot\)) indicates the number of water molecules that are systematically incorporated in the crystals of the compound. In this case, the number five suggests there are five water molecules associated with each formula unit of \(\mathrm{CuSO}_{4}\).

Determine the Number of Water Molecules

Since the number five is directly next to the hydrate notation, it shows that there are five water molecules bonded. Therefore, we can conclude that five hydrogen bonded water molecules are associated with each unit of \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\).

Key concepts

Copper(II) sulfate pentahydrate

Copper(II) sulfate pentahydrate, written scientifically as \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\), is a bright blue crystalline solid that is widely used in the field of chemistry, particularly in chemical education due to its vivid color and interesting properties. Hydrates like this compound are substances that contain water molecules within their crystal structure. The water is not just trapped; it is chemically bonded to the substance.

When discussing hydrates, the water molecules included in the chemical formula are indicative of a fixed ratio in which they combine with the rest of the compound. In the case of Copper(II) sulfate pentahydrate, each formula unit of Copper(II) sulfate (\(\mathrm{CuSO}_{4}\)) is associated with exactly five water molecules (\(\mathrm{H}_{2}\mathrm{O}\)). This specific number of water molecules directly impacts the properties of the compound, contributing to aspects like its shape, color, and even its stability.

Chemical Formula Notation

Understanding chemical formula notation is fundamental in the study of chemistry. It is a way of representing the composition of chemical compounds using symbols and numbers. Each element is represented by its unique chemical symbol, with a subscript number indicating the number of atoms of that element in one molecule of the compound.

In hydrates, a special notation is used where a dot (\(\cdot\)) separates the compound from the number of water molecules it includes. This dot is not just a placeholder; it indicates that the water is chemically bound to the compound in a specific ratio. For example, the notation for Copper(II) sulfate pentahydrate (\(\mathrm{CuSO}_{4}\cdot 5 \mathrm{H}_{2}\mathrm{O}\)) clearly shows that five molecules of water are coordinated to the Copper(II) sulfate unit. This kind of notation provides a quick overview of the composition of hydrates, which is crucial when predicting their chemical behavior and physical properties.

Hydrogen Bonding

Hydrogen bonding is a type of chemical bond that is fundamental to the structure and properties of many compounds, including water and hydrates. It involves a hydrogen atom that is bound to a strong electronegative element (such as oxygen, nitrogen, or fluorine) and another electronegative element on a neighboring molecule or within the same molecule.

In hydrates like Copper(II) sulfate pentahydrate, the water molecules are attached to the salt through hydrogen bonds. These bonds are critical to the integrity and stability of the hydrate's crystal lattice structure. They play a key role in determining the compound's melting and boiling points, solubility, and many other physical characteristics. Understanding the role of hydrogen bonding helps explain why certain hydrates can lose their water molecules when heated, changing their structure and, subsequently, their properties.