Question

Supply a systematic name for each of the following hydrate compounds: (a) \(\mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2} \cdot 4 \mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3} \cdot 9 \mathrm{H}_{2} \mathrm{O}\)

Short answer

(a) Strontium nitrate hexahydrate (b) Cobalt(II) acetate tetrahydrate (c) Copper(II) sulfate pentahydrate (d) Chromium(III) nitrate nonahydrate

Step-by-step solution

Understand the Compound Components

Hydrates are compounds that include a specific number of water molecules in their structure. The chemical formula (1) \( \mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2} \cdot 6 \mathrm{H}_{2}\mathrm{O} \) (2) \( \mathrm{Co}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2} \cdot 4 \mathrm{H}_{2} \mathrm{O} \) (3) \( \mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O} \) (4) \( \mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3} \cdot 9 \mathrm{H}_{2}\mathrm{O} \) represent the hydration of ionic compounds with water. We need to identify the ionic compound and its accompanying water molecules.

Name the Anhydrous Compound

For each hydrate, identify and name the compound without water (anhydrous compound):(a) \( \mathrm{Sr} \left( \mathrm{NO}_{3} \right)_{2} \) is strontium nitrate.(b) \( \mathrm{Co} \left( \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2} \right)_{2} \) is cobalt(II) acetate.(c) \( \mathrm{CuSO}_{4} \) is copper(II) sulfate.(d) \( \mathrm{Cr} \left( \mathrm{NO}_{3} \right)_{3} \) is chromium(III) nitrate.

Identify the Number of Water Molecules

Determine the number of water molecules associated with each hydrate, specified by the dot in the chemical formula: (a) 6 water molecules. (b) 4 water molecules. (c) 5 water molecules. (d) 9 water molecules.

Assign the Systematic Name for the Hydrate

Combine the name of the anhydrous compound with the term for the number of water molecules (hydrate prefix) and the word 'hydrate':(a) The prefix for 6 is 'hexa', so \( \mathrm{Sr} \left( \mathrm{NO}_{3} \right)_{2} \cdot 6 \mathrm{H}_{2}\mathrm{O} \) is strontium nitrate hexahydrate.(b) The prefix for 4 is 'tetra', so \( \mathrm{Co} \left( \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2} \right)_{2} \cdot 4 \mathrm{H}_{2} \mathrm{O} \) is cobalt(II) acetate tetrahydrate.(c) The prefix for 5 is 'penta', so \( \mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2}\mathrm{O} \) is copper(II) sulfate pentahydrate.(d) The prefix for 9 is 'nona', so \( \mathrm{Cr} \left( \mathrm{NO}_{3} \right)_{3} \cdot 9 \mathrm{H}_{2}\mathrm{O} \) is chromium(III) nitrate nonahydrate.

Key concepts

Systematic Naming

Systematic naming is a structured way to name chemical compounds in order to clearly communicate their composition and properties. It's particularly important in chemistry as it helps avoid confusion that common names might cause. When dealing with hydrate compounds, systematic naming involves two main parts: naming the anhydrous compound first, followed by the water content.

For example, take the compound \( \mathrm{Sr}\left(\mathrm{NO}_3\right)_2 \cdot 6 \mathrm{H}_2\mathrm{O} \). The base or anhydrous part, \( \mathrm{Sr}\left(\mathrm{NO}_3\right)_2 \), is named strontium nitrate. The second part involves counting the number of water molecules attached. Since there are six water molecules, the prefix "hexa-" is used. Thus, it becomes strontium nitrate hexahydrate.

This naming convention helps easily identify the composition of hydrates and allows chemists and students alike to communicate effectively and precisely about chemical formulas.

Anhydrous Compounds

Anhydrous compounds are substances that remain after the removal of water molecules. The term 1anhydrous' comes from Greek origins, meaning 'without water'. In hydrates, water is part of their structure but can be temporarily removed, leaving behind the anhydrous form of the compound.

Consider the example of \( \mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O} \). This is known as copper(II) sulfate pentahydrate. If you remove the water, you are left with simply copper(II) sulfate, an anhydrous compound.

Anhydrous compounds frequently appear in industrial and laboratory settings, commonly used due to their high reactivity relative to their hydrated forms. Knowing how to swiftly determine and handle both forms can be a valuable skill for anyone working in the chemical sciences.

Hydration of Ionic Compounds

Hydration of ionic compounds involves the bonding of water molecules with the ionic compounds. These water molecules integrate into the crystal lattice structure, sometimes affecting the properties of the compound, such as solubility and color.

The process of hydration simplifies the way we view the relationship between water molecules and salts in many ionic compound reactions. In chemical formulas, hydration is denoted with a dot, followed by the number of water molecules. For instance, the formula \( \mathrm{Cr}\left(\mathrm{NO}_3\right)_3 \cdot 9 \mathrm{H}_2 \mathrm{O} \) shows that 9 molecules of water are closely associated with chromium(III) nitrate.

• The presence of water is indicated by the 'hydrate' suffix.
• Each fixed number of water molecules is shown by specific prefixes, such as "mono-" for one, "di-" for two, "tri-" for three, and so forth.
• Hydrated compounds exhibit unique physical and chemical properties compared to their anhydrous counterparts.

This interaction isn't just about mixing; it involves intricate processes at a molecular level that can be crucial for understanding chemical behavior and reactions.