Hydrogen & Hydroxide Ions
Hydrogen 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)
Hydroxide ions
- 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)
Examiner Tip
Acids
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
