Acids and Bases 8.1-8.4

Question 1

What did Antoine Lavoiser think?

Answer 1

He believed that oxygen was present in all acids. He gave them the name ‘oxygene’, these theory was key disproving the phlogiston theory but was wrong. This was proved wrong when they discovered the acid HCL, and realised that it was hydrogen not oxygen that was essential.

Question 2

What is an acid? Arrhenius’s theory

Answer 2

A substance that ionises in water to produce hydrogen ions.

Question 3

What is an alkali? Arrhenius’s theory

Answer 3

A substance that ionises in water to produce hydroxide ions.

Question 4

What is a neutralisation reaction?

Answer 4

The combination of an acid and a base, involving the combination of a hydroxide and a hydrogen ion.

Question 5

What is the Bronsted - Lowry theory?

Answer 5

They referred to a hydrogen ion as a proton, and therefore an acid could be referred to as a proton donator and an alkali as a proton acceptor. A Bronsted - Lowry acid is therefore one that donates a proton and a Bronsted - Lowry base is one that accepts a proton.

Question 6

What is a hydronium ion?

Answer 6

The hydronium ion H3O+ is formed when water forms a coordinate bond with water.

Question 7

What is a conjugate acid - base pair?

Answer 7

A conjugate acid base pair differ by one proton. So water H30+ is the conjugate acid, H20 is therefore the conjugate base. But water also has an OH- ion so we can say that water is amphiprotic.

Question 8

What is an amphiprotic species?

Answer 8

Substances that can act as either a Bronsted - Lowry base or a Bronsted - Lowry acid. For example water, which can be both H30+ or OH-. Amino acids also act as an amphiprotic species, because they can be both acidic or alkaline with the zwitterion form in the middle.

Question 9

What colour does phenolphthalein turn in acids and alkalis?

Answer 9

Acids - colourless

Alkali - pink

Question 10

What colour does methyl orange turn in acids and alkalis?

Answer 10

Acids - red

Alkalis - yellow

Question 11

What does an acid and a metal/metal oxide/hydroxide/hydrocarbonates/carbonates form?

Answer 11

A salt.

Question 12

Which reactions with acids form a salt and hydrogen?

Answer 12

Metals above hydrogen in the reactivity series.

Question 13

What do acids and metals above hydrogen in the reactivity series form?

Answer 13

A salt and hydrogen.

Question 14

What is the standard enthalpy change of neutralisation?

Answer 14

The energy change when one mole of water from the reaction between a strong acid and a strong base is formed under standard conditions.

Question 15

How does calcium oxide react with aqueous acids?

Answer 15

Calcium oxide does not react directly with aqueous acids. This base dissolves in water to create an alkaline solution of calcium hydroxide, which neutralises, the acid:
CaO + H20 - Ca(OH)2
Calcium hydroxide is slightly soluble in water and therefore an alkali.

Question 16

What does a metal carbonate/metal hydrocarbonate and an acid produce?

Answer 16

Salt and carbon dioxide and water.

Question 17

What is the difference between amphiprotic and amphoteric?

Answer 17

Amphiprotic substances refers to the Bronsted - Lowry definition of an acid and a base, and suggests that the substance can both have ions able to donate and accept a proton. Whereas amphoteric is a more general term and refers to the quality of a substance to react with both an acid and a base. All amphiprotic substances are amphoteric but not all amphoteric substances are amphiprotic.

Question 18

What is the difference between the Bronsted - Lowry definition of an acid and the Lewis definition of an acid?

Answer 18

The Bronsted - Lowry definition defines an acid as a proton donor, whereas the Lewis definition defines it as an electron pair acceptor, so it is the reverse. The bases are the opposite, an acceptor by the Bronsted - Lowry definition and a electron pair donor via the Lewis definition. The Lewis definition is more general than the Bronsted - Lowry and can be applied to reactions that do not include the transfer of protons. The Lewis definition covers all the Bronsted - Lowry reactions because the acceptance of a proton by a base must involve the donation of an electron pair to the proton. For example the reaction between BF3 and NH3 is a Lewis reaction but not a Bronsted - Lowry one.
NH3 + BF3 = N3H:BF3
This involves the transfer of electrons but not the transfer of a proton.

Question 19

What is a Lewis base acid reaction?

Answer 19

This is the transfer of a pair of electrons and can involve things like forming a complex ion, which makes it a more general definition than the Bronsted - Lowry one. A coordinate or dative bond is always formed in a Lewis acid base reaction.
Fe2+ + 6H2O = (Fe(H2O)2)2+
The transition metal accepts electrons, getting a less positive charge and therefore is the Lewis acid. The water donates electrons and therefore is the Lewis base.

Question 20

What makes something a Lewis acid or a Lewis base?

Answer 20

For a substance to act as a Lewis base, it must have a lone pair of electrons. For a substance to act as a Lewis acid it must have the ability to accept a lone pair of electrons.

Question 21

How do you make a salt from an acid?

Answer 21

The hydrogen atom in the acid can be seen as replaceable, and can be replaced by a metal ion to form a salt if it is more reactive than hydrogen.

Question 22

How does an acid react with a metal?

Answer 22

Metal + acid = salt + hydrogen

Question 23

How does an acid react with a carbonate or a hydrocarbonate?

Answer 23

Acid + carbonate/hydrocarbonate = salt + carbon dioxide + water.

Question 24

How does an acid react with an alkali?

Answer 24

Base + acid = salt + water
This is a neutralisation reaction and usually involved the combination of a H+ ion and a OH- ion. Neutralisation reacts are usually exothermic.