Acids and bases

Question 1

What are the common acids that you need to know?

Answer 1

1. Sulphuric acid
2. Hydrochloric acid
3. Nitric acid
4. Ethanoic acid
5. Phosphoric acid

Question 2

What does an acid do when it dissolves/added in water?

Answer 2

It dissociates. When an acid is added to water releases H+ ions when split up.

Question 3

An acid is:

Answer 3

A species that is a proton donor.

Question 4

A strong acid:

Answer 4

Fully dissociates

Question 5

A weak acid

Answer 5

Partially dissociates

Question 6

Common bases (metal oxides/hydroxides) that you need to know are:

Answer 6

1. Magnesium oxide
2. Copper (II) oxide
3. Potassium hydroxide
4. Sodium hydroxide
5. Ammonia

Question 7

A base is:

Answer 7

A proton acceptor

Question 8

What is the equation for the dissociation of sodium hydroxide in water?

Answer 8

NaOH(s) + aq -> Na+(aq) + OH-(aq)

Question 9

An alkali is:

Answer 9

A base that dissolves in water forming hydroxide ions.

Question 10

What is the equation for when ammonia dissolves in water to form a weak base?

Answer 10

NH3(g) + aq -> NH4+(aq) +OH-(aq)
(reversible reaction)

Question 11

What is the ionic equation for the reaction of ANY acid with ANY alkali?

Answer 11

H+(aq) + OH-(aq) -> H2O(l)

Question 12

Acid + base ->

Answer 12

water + salts

Question 13

Acid + alkali ->

Answer 13

salt + water

Question 14

Acid + carbonate ->

Answer 14

Salt + water + carbon dioxide

Question 15

What is the method of preparation for preparing a standard solution?

Answer 15

1. Weigh the solid accurately (using a balance)
2. Dissolve and then transfer the solid in a beaker (do not fill)
3. Transfer solution to a 250cm3 volumetric flask. Rinse traces of solution from the beaker into flask.
4. Carefully fill the volumetric flask to the graduation line. (Read the meniscus at the bottom of the curve).
5. Invert the flask several times to ensure well mixed.

Question 16

State and explain the effect on the titre of filling the flask with water above the graduation line.

Answer 16

The volume will be larger so the concentration is lower meaning there are fewer moles present.

Question 17

State and explain the effect on the titre of not inverting the flask.

Answer 17

Smaller titre because fewer moles are present in a lower concentration solution.
Inconsistent titres due to concentration of standard solution.

Question 18

What is the method of carrying out the titration?

Answer 18

1.Using a pipette, we measure a volume of a solution into a conical flask.
2. The other solution is placed in a burette and the volume recorded (initial volume).
3. A few drops of indicator are added to the solution in the conical flask.
4. The solution in the burette is then added to the solution in the conical flask until the reaction has just completed. This is called the end point (we see a colour change). The volume in the burette is recorded (final volume).
5. The volume of solution added from the burette is calculated. This is known as a titre.
6. The experiment is repeated until two titres are concordant (to 0.1cm3).
7. The mean titre is calculated to 2 d.p. Only concordant titres are used in the mean. Do not use trial as it is approx.

Question 19

State and explain the effect on volume of the titre if the following error takes place: The pipette has an air bubble inside.

Answer 19

A larger volume of titre, as solution used to fill the jet.

Question 20

State and explain the effect on volume of the titre if the following error takes place: The burette readings are taken from the top of the meniscus.

Answer 20

It is relative as long as it happens at the start and at the end.

Question 21

How do calculate unknowns? (basic)

Answer 21

1. Write balanced equation
2. Find the mol of thing you know most about.
3. Use the balanced equation to find the mol of the unknown.
4. Calculate the concentration in mol dm-3 of the unknown.