acids, bases and salts

Question 1

what is the pH scale used for?

Answer 1

to measure the acidity or alkalinity of a solution

- can be measured using a universal indicator or a pH probe

Question 2

what ions do acidic solutions release in aqueous solutions?

Answer 2

hydrogen ions [H+]

Question 3

what is an alkali?

Answer 3

a base that dissolves in water

Question 4

what do strong acids do in an aqueous solution?

Answer 4

completely dissociate to release H+ ions

Question 5

what do weak acids do in an aqueous solution?

Answer 5

partially dissociate to release H+ ions

Question 6

examples of strong acids:

Answer 6

• hydrochloric
• nitric
• sulphuric

Question 7

examples of weak acids:

Answer 7

• ethanoic
• citric
• carbonic

Question 8

what ions do alkali solutions contain?

Answer 8

hydroxide ions [OH-]

Question 9

what do strong bases do in an aqueous solution?

Answer 9

fully dissociate to release OH- ions

Question 10

what do weak bases do in an aqueous solution?

Answer 10

partially dissociate to release OH- ions

Question 11

examples of strong bases:

Answer 11

• sodium hydroxide

- potassium hydroxide

Question 12

examples of weak bases:

Answer 12

• ammonia

- ammonium hydroxide

Question 13

what is the reaction of an acid and a metal?

Answer 13

acid + metal —> salt + hydrogen

Question 14

what is the reaction of an acid and an alkali?

Answer 14

acid + alkali —> salt + water

Question 15

what is the reaction of an acid and a base?

Answer 15

acid + base —> salt + water

Question 16

what is the reaction of an acid and a metal carbonate?

Answer 16

acid + metal carbonate —> salt + water + carbon dioxide

Question 17

what do each of these produce:
     -  HCl
     -  HNO3
     -  H2SO4
?

Answer 17

• hydrochloric acid produces chlorides
• nitric acid produces nitrates
• sulphuric acid produces sulphates

Question 18

what is the method for preparing soluble salts?

Answer 18

1. measure a set volume of your acid
2. gently heat the acid
3. add the chosen base in excess [until no more will dissolve]. you know when the acid has been neutralised when the excess solid sinks to the bottom
4. filter the excess base using filter paper and a funnel
5. heat the salt solution to evaporate the water [to make the solution more concentrated]
6. leave the rest to evaporate slowly so crystals of the salt form

Question 19

why is a titration performed?

Answer 19

to find out the volume or concentration of acid and alkali solutions the react with eachother

Question 20

what is the process of a titration?

Answer 20

1. add acid to burette using a funnel, record the start volume of the burette
2. add a known volume of alkali to a conical flask and add a few drops of indicator
3. place the conical flask on a white tile so you can see the colour change clearly
4. turn the tap of the burette to slowly add acid to alkali until you reach the neutralisation point when the indicator changes colour
5. calculate the volume of acid, this is called the titre
6. repeat until you get concordant titres [within 0.1cm^3 of each other]

Question 21

what is the equation for moles?

Answer 21

moles = concentration x volume

Question 22

what is the equation for concentration?

Answer 22

concentration = moles / volume

Question 23

what are the units of concentration?

Answer 23

mol/dm^3

Question 24

what is the test for carbon dioxide gas?

Answer 24

bubble the gas through limewater and it ill turn milky if carbon dioxide is present

Question 25

what is the test for carbonates?

Answer 25

• carbonates react with dilute acids to create carbon dioxide
• this gas can then be bubbled through limewater, if limewater goes cloudy, the gas is CO2

Question 26

what is the test for sulphate ions?

Answer 26

• first add dilute hydrochloric acid, followed by barium chloride solution
• a white precipitate will form if sulphate ions are in the solution