Hydrogen & Hydroxide Ions

Acids have pH values of below 7, have a sour taste (when edible) and are corrosive
Acids are substances that can neutralise a base, forming a salt and water
Acids contain hydrogen ions (H⁺)
The presence of H⁺ ions is what makes a solution acidic

Example; hydrochloric acid

HCl (aq) → H⁺ (aq) + Cl^– (aq)

Alkalis have pH values of above 7 (a base which is water-soluble is referred to as an alkali)
They are substances which can neutralise an acid, forming a salt and water
Alkalis contain hydroxide ions (OH^–)
The presence of the OH^– ions is what makes the aqueous solution an alkali

Example; sodium hydroxide

NaOH (s) → Na⁺ (aq) + OH^– (aq)

Acids harm-corrosive-oxidising

Hazard symbols you may see in relation to acids

The hazards associated with acids depend on the type and concentration of the acid
Most dilute acids either require no hazard symbol or they are an irritant, so require the symbol to show they are harmful to health
- Eye protection should be worn when handling
Moderately concentrated acids are often corrosive
- In addition to eye protection, gloves should also be worn
Some concentrated acids, e.g. nitric acid, are oxidising which can cause or intensify a fire in contact with combustible materials
- Eye protection and gloves are necessary when handling concentrated acids and the use of a fume cupboard is often required

Hydrogen & Hydroxide Ions (WJEC GCSE Chemistry: Combined Science)