Question

Chemically borax is (a) sodium metaborate (b) sodium orthoborate (c) sodium tetraborate decahydrate (d) sodium hexaborate.

Short answer

Borax is chemically known as sodium tetraborate decahydrate.

Step-by-step solution

Understanding Borax Composition

Begin by recalling the chemical formula for borax, which is Na2B4O7·10H2O. Knowing the composition of the ions in this compound can help us match it to the correct chemical name.

Analyzing the Chemical Name Options

Match the chemical formula to the correct chemical name by comparing each option against the borax formula. Sodium metaborate would be NaBO2, sodium orthoborate would be Na3BO3, sodium tetraborate decahydrate is Na2B4O7·10H2O, and sodium hexaborate would have six boron atoms per formula unit.

Identifying the Correct Chemical Name

Determine the correct name based on the structure of the borax formula; it must reflect the correct number of boron atoms, sodium atoms, and water molecules. The formula Na2B4O7·10H2O indicates that there are four boron atoms and it is hydrated with ten water molecules, which corresponds with 'sodium tetraborate decahydrate'.

Key concepts

Sodium Tetraborate Decahydrate

Sodium tetraborate decahydrate is most commonly known as borax. It's a natural mineral and salt of boric acid that is widely used in household products such as cleaners, laundry detergents, and even as an insecticide. Its chemical formula, Na₂B₄O₇·10H₂O, reveals key aspects of its composition: it consists of two sodium atoms (Na), four boron atoms (B), seven oxygen atoms (O), and is hydrated with ten water molecules (10H₂O).

The term decahydrate is crucial as it indicates that for every molecule of borax, there are ten molecules of water, making it a hydrated compound. This hydration is significant because it affects the substance's properties such as its solubility, crystalline structure, and stability.

Chemical Composition of Borax

Understanding the chemical composition of borax is essential for its identification and use in various applications. The molecule is made up of sodium, boron, and oxygen, which together form the borate ion, B₄O₇, and is balanced by sodium ions. One molecule of borax can be dissected into two units of the Na⁺ ion and one unit of the B₄O₇^2- ion.

The presence of water molecules in borax is where the term 'decahydrate' comes from. When borax is heated and the water of hydration is lost, it converts into a different substance called anhydrous sodium tetraborate. The removal or addition of water can change the properties drastically, which is why the decahydrate part of its name, and its presence, is essential in characterizing borax.

Analyzing Chemical Names

The name of a chemical compound provides a wealth of information about its structure and makeup, which is evident in the example of borax. Analyzing chemical names involves breaking down the terms used to denote the compound's constituents and their proportions. For instance, in the name sodium tetraborate decahydrate, sodium refers to the Na⁺ element present, tetraborate reveals the presence of four boron atoms as part of the borate ion, and decahydrate indicates that there are ten water molecules associated with each molecule of the substance.

Names like metaborate, orthoborate, or hexaborate suggest different numbers of boron atoms and different chemical structures. Understanding these terms is key to decoding the formula of a compound, as seen when matching the formula Na₂B₄O₇·10H₂O to its proper chemical name, reinforcing its identity as sodium tetraborate decahydrate.