What are the characteristic properties of bases?

Bases are substances that can accept protons, react with acids, and have a pH greater than 7.

Bases, also known as alkalis, are substances that have the ability to accept protons (H+ ions) or donate a pair of electrons. This property is the opposite of acids, which are proton donors. Bases can react with acids in a reaction called neutralisation, where the acid and base cancel each other out to form a salt and water. This is a key characteristic of bases and is often used in practical applications such as antacid tablets, which contain a base to neutralise excess stomach acid.

Another important characteristic of bases is their pH. The pH scale is used to measure how acidic or basic a substance is, with 7 being neutral. Bases have a pH greater than 7, up to a maximum of 14. This is because they produce hydroxide ions (OH-) when dissolved in water, which increases the pH. The higher the concentration of hydroxide ions, the more basic the solution is and the higher its pH.

Bases also have certain physical properties. Many bases are solid and are often found in everyday items such as baking soda and cleaning products. They can feel slippery to the touch, which is due to the reaction of the base with the oils on your skin. Bases can also be corrosive, meaning they can cause damage to materials, including skin, on contact.

In terms of chemical structure, bases often contain the hydroxide (OH-) ion, but this is not always the case. Some bases, such as ammonia (NH3), do not contain a hydroxide ion but can still accept protons and react with acids. This is because the nitrogen atom in ammonia has a lone pair of electrons, which can accept a proton to form a positively charged ammonium ion (NH4+).