Topic 8 : Acids and Bases Flashcards
The Brønsted-Lowry Theory
- The Brønsted-Lowry Theory defines acids and bases in terms of proton transfer between chemical compounds
- A Brønsted-Lowry acid is a species that gives away a proton (H+)
- A Brønsted-Lowry base is a species that accepts a proton (H+) using its lone pair of electrons
- The Brønsted-Lowry Theory is not limited to aqueous solutions only and can also be applied to reactions that occur in the gas phase
Conjugate acid-base pairs
- A conjugate acid-base pair is two species that are different from each other by a H+ ion
- Conjugate here means related
- In other words, the acid and base are related to each other by one proton difference
Amphiprotic Species
- Species that can act both as proton donors and acceptors are called amphiprotic
- Eg. water as a Brønsted-Lowry acid
amphiprotic and amphoteric
- A compound that is amphoteric means it has both basic and acidic character. When the compound reacts with an acid, it shows that it has basic character. When it reacts with a base, it shows that it’s acidic
- An example of amphoteric is aluminium oxide
- When a compound is amphiprotic, it means it can act as a proton donor and as a proton acceptor
- Aluminium oxide is not amphiprotic, even though it is amphoteric
Difference between amphiprotic and amphoteric
- Amphiprotic describes a substance that can accept and donate a proton or H+ while amphoteric means the ability to act as both an acid and a base
- All amphiprotic substances are amphoteric but not all amphoteric substances are amphiprotic
Reaction between metals and acids
- acid + metal → salt + hydrogen
- the extent of reaction depends on the reactivity of the metal and the strength of the acid
- Metals low in reactivity do not react at all, for instance copper does not react with dilute acids
- Stronger acids will react more vigorously with metals than weak acids.
- Using stronger acids will make the reaction more exothermic and the metal will dissolve faster
Reaction between metals and oxides
- acid + metal oxide → salt + water
Reaction between metals and hydroxides
acid + metal hydroxide → salt + water
Reaction between metals and carbonates
- acid + metal carbonate → salt + water + carbon dioxide
Reaction between metals and hydrogen carbonates
acid + metal hydrogencarbonate → salt + water + carbon dioxide
Neutralization Reaction
- A neutralisation reaction is one in which an acid (pH <7) and a base/alkali (pH >7) react together to form water (pH = 7) and a salt
- The proton of the acid reacts with the hydroxide of the base to form water
- The spectator ions which are not involved in the formation of water, form the salt
Acid + Base (alkali) → Salt + Water
S
Salt produced in neutralization reaction with hydrochloric acid
a chloride
Salt produced in neutralization reaction with nitric acid
A nitrate
Salt produced in neutralization reaction with sulfuric acid
a sulfate
Acid-Base Titration
- Acid-base titrations are used to find the unknown concentrations of solutions of acids and bases
Acid-Base Indicators
- Acid-base indicators give information about the change in chemical environment. They change colour reversibly depending on the concentration of H+ ions in the solution
- Indicators are weak acids and bases where the conjugate bases and acids have a different colour
- Many acid-base indicators are derived from plants, such as litmus
- A good indicator gives a very sharp colour change at the equivalence point
Litmus paper in acid and alkali
Acid - Pink
Alkali - Blue
Methyl Orange in acid and alkali
Acid - Red
Alkali - Yellow
Phenolphthalein in acid and alkali
Acid - colourless
Alkali - Pink