Spread the ions

The idea

Mixing an acid or a base with water decreases the concentration of ions (H3O+/OH–) per unit volume; this process is called dilution.

One more cup of water

A strong acid has 24 H₃O⁺ ions packed in a few squares of water. You add a lot more water.

How many ions will each square of water hold now?

• Fewer
• More
• The same

Add water

Press Add water twice. Watch the ions per square. Then try the base.

Same ions, more room

Mixing an acid or a base with water decreases the concentration of ions (H₃O⁺ or OH⁻) per unit volume. This is dilution. The acid or base is said to be diluted.

A diluted acid has fewer H₃O⁺ in each unit of volume, and a diluted base has fewer OH⁻.

• Strong | After adding water
• Water | less | more
• Ions per unit volume | more | fewer

Notes

Mixing an acid or a base with water decreases the concentration of ions (H₃O⁺/OH⁻) per unit volume; this process is called dilution.

Check yourself

What is dilution?

24 ions are spread through 12 equal squares of water. How many ions are in each square?

Answer: 2 ions

24 ÷ 12 = 2 ions in each square.

You add water to a base. What falls?

Which solution has more H₃O⁺ ions in the same volume?

• Adding more acid, so ions per unit volume rise. That makes it stronger. Dilution is adding water.
• Heating the solution. Dilution is about adding water, not heat.
• Adding water, so ions per unit volume fall — correct. Yes!
• OH⁻ ions per unit volume — correct. Yes! The base is diluted.
• H₃O⁺ ions per unit volume. A base is about OH⁻. Its OH⁻ per unit volume falls.
• Nothing changes. The same ions have more water to spread through.
• The acid after adding water. After adding water there are fewer per unit volume.
• The acid before adding water — correct. Yes! Adding water spreads the ions out.
• Both the same. Dilution changes how many ions are in each unit of volume.