Equivalent (chemistry) facts for kids

An equivalent (often shortened to Eq) is a way to measure the amount of a substance. It tells us how much of one substance will react with a certain amount of another substance in a chemical reaction. Think of it like matching up puzzle pieces – an equivalent helps us know how many pieces of one type fit with another.

This idea was used a lot in the past in chemistry and biology. The mass of an equivalent is called its equivalent weight.

What is an Equivalent?

In chemistry, an equivalent is the amount of a substance that can do one of these things:

• React with or provide one mole of hydrogen ions (H⁺) in an acid–base reaction.
• React with or provide one mole of electrons in a redox reaction (a reaction where electrons are moved).

These "reaction units" (like hydrogen ions or electrons) help us understand how substances combine.

Equivalents in Solutions

When we talk about ions (atoms with an electrical charge) in a solution, the number of equivalents is found by multiplying the number of moles of that ion by its valence. Valence is like the "combining power" of an atom.

For example, imagine a solution with 1 mole of sodium chloride (NaCl) and 1 mole of calcium chloride (CaCl₂).

• Sodium (Na⁺) has a valence of 1. So, 1 mole of Na⁺ is 1 equivalent.
• Calcium (Ca²⁺) has a valence of 2. So, 1 mole of Ca²⁺ is 2 equivalents.
• Chloride (Cl^-) has a valence of 1. In this solution, there are 3 moles of Cl^- (1 from NaCl, 2 from CaCl₂), so there are 3 equivalents of Cl^-.

Equivalents in Medicine

In biological systems, like inside our bodies, chemical reactions happen with very tiny amounts of substances. Because of this, scientists and doctors often use milliequivalents (often written as mEq or meq). The word "milli" means one-thousandth (1/1000). So, 1 milliequivalent is 1/1000 of an equivalent.

Often, you'll see measurements like milliequivalents per litre of solution (mEq/L). This is very common for measuring substances in biological fluids, like blood. For example, a healthy level of potassium in human blood is usually between 3.5 and 5.0 mEq/L.

Why use Milliequivalents?

Milliequivalents are useful because they account for the charge of an ion.

• An ion with a single charge (like Na⁺ or Cl^-) provides the same number of milliequivalents as its millimoles. So, 1 millimole (0.001 mole) of Na⁺ is 1 mEq.
• An ion with two charges (like Ca²⁺) provides twice the number of milliequivalents as its millimoles. So, 1 millimole of Ca²⁺ is 2 mEq.

This helps doctors understand the balance of charged particles in the body, which is very important for health.

See also

In Spanish: Equivalente para niños