Carboxylic Acids

Question 1

What type of functional group do carboxylic acids contain?

Answer 1

A carboxyl functional group: carbonyl group and a hydroxyl group.

Question 2

Why are carboxylic acids polar?

Answer 2

Because the C=O and O-H bonds are electronegative so are polar.

Question 3

What can carboxylic acids do as they are polar?

Answer 3

Form hydrogen bonds with water molecules.

Question 4

What is the solubility of carboxylic acids like? (2)?

Answer 4

1. Carboxylic acids with up to four carbon atoms are soluble in water.
2. As the number of carbon atoms increases, the solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule.

Question 5

What bonds form between the O on the C=O bond in carboxylic acids and the H molecule of water?

Answer 5

Hydrogen bonds.

Question 6

What are dicarboxylic acids?

Answer 6

They have two polar carboxyl groups to form hydrogen bonds.

Question 7

What are 2 properties of dicarboxylic acids?

Answer 7

1. Solid at room temperature.
2. Dissolve readily in water.

Question 8

What type of acids are carboxylic acids? E.g.?

Answer 8

Weak acids as they partially dissociate when dissolved in water, e.g. methanoic acid.

Question 9

What are the two acid reactions of carboxylic acids?

Answer 9

1. Redox reactions with metals.
2. Neutralisation reactions with bases (alkalis, metal oxides, and metal carbonates).

Question 10

What is formed in these reactions?

Answer 10

Carboxylate salts.

Question 11

How are carboxylate salts named?

Answer 11

The carboxylate ion in the salt has the suffix of ‘-ate’.

Question 12

What is the equation for redox reactions of carboxylic acids with metals? Observation?

Answer 12

• Carboxylic Acid + Metal = Hydrogen gas + Carboxylate Salt.
• You would observe the metal disappearing and effervescence as hydrogen gas is evolved.

Question 13

What is the equation for neutralisation reactions of carboxylic acids with metal oxides?

Answer 13

Carboxylic Acid + Metal Oxide = Salt (calcium ethanoate) + Water.

Question 14

What is the equation for neutralisation reactions of carboxylic acids with alkalis?

Answer 14

Carboxylic Acid + Alkali = Salt (sodium ethanoate) + Water.

Question 15

What may be observed in the reaction between carboxylic acids with alkalis in neutralisation reactions

Answer 15

No reaction as two solutions react together to form an aqueous solution of the salt.

Question 16

What is the ionic equation for a neutralisation reaction?

Answer 16

H+ (aq) + OH- (aq) = H2O (l).

Question 17

What is the equation for neutralisation reactions of carboxylic acids with carbonates?

Answer 17

Carboxylic Acid + Carbonate = Salt (sodium ethanoate) + Water + Carbon Dioxide.

Question 18

What would happen if the carbon dioxide evolved was in excess in the neutralisation reaction of carboxylic acids with carbonates?

Answer 18

A solid carbonate would disappear.

Question 19

How do you test for a carboxyl group?

Answer 19

With the neutralisation of carboxylic acids with carbonates as carboxylic acids are the only common organic product that is sufficiently acidic to react with carbonates. Specifically to distinguish between carboxylic acids and phenols because phenols are not acidic enough to react with carbonates.

Question 20

Do longer chain carboxylic acids have higher or lower solubility than shorter chain carboxylic acids?

Answer 20

Shorter carboxylic acid chains have a higher solubility because the percentage of the OH group has a greater effect on the solubility.