Acids, Alkalis and Salts

Question 1

What colour does bromothymol blue go in acids and alkalis?

Answer 1

Acids: Yellow
Alkalis: Light Blue

Question 2

What colour does methyl orange go in acids and alkalis?

Answer 2

Acids: Red
Alkalis: Yellow

Question 3

What colour is phenolphthalein in acids and alkalis?

Answer 3

Acids: Colourless
Alkalis: Purple, Pink

Question 4

What are ions are acids the sources of?

Answer 4

Hydrogen, H+

Question 5

What ions are alkalis the source of?

Answer 5

Hydroxide, OH-

Question 6

What colour is litmus in acids, neutral and alkalis?

Answer 6

Acids: Red
Neutral: Purple
Alkalis: Blue

Question 7

What is an acid?

Answer 7

• Source of H+ ions
• pH less than 7
• Release H+ ions of dissolved in water
• ‘Dissociate in water to produce hydrogen ions’

Question 8

What is a base?

Answer 8

• Can neutralise an acid

Question 9

What is the difference between bases and alkalis?

Answer 9

An alkali is a soluble base. It is a source of OH- ions. They have pH above 7.

Question 10

Acid + Base

Answer 10

Acid + Base -> Salt + Water

Question 11

Give examples of a strong and weak acids.

Answer 11

Strong: Sulphuric
Weak: Vinegar, Lemon Juice, Bee Sting

Question 12

Give examples of neutral substances.

Answer 12

Distilled water, salt water

Question 13

Give examples of weak and strong alkalis.

Answer 13

Weak: Baking powder, Ammonia
Strong: Sodium Hydroxide

Question 14

What colours does universal indicator turn in different pHs?

Answer 14

Strong acid: Red
Weak acid: Yellow
Neutral: Green
Weak alkali: Blue
Strong alkali: Purple

Question 15

What is the difference between hydrogen chloride and hydrochloric acid?

Answer 15

In water, hydrogen gas dissolves to form hydrochloric acid. The solution is acidic because the hydrogen chloride dissociates into H+ and Cl- ions. pH is a measure of H+ ions, so it is acidic. Hydrogen chloride as a gas is not acidic.

Question 16

What is the state of hydrogen chloride in room temperature?

Answer 16

Gas

Question 17

Acid + Carbonate

Answer 17

Acid + Carbonate -> Salt + Water + Carbon Dioxide

Question 18

Acid + Metal

Answer 18

Acid + Metal -> Salt + Hydrogen

Question 19

How do H+ ions and OH- ions react?

Answer 19

H+ + OH- -> H2O

Question 20

What happens to H+ ions in water?

Answer 20

They attach themselves to water molecules:

H+ + H2O -> H3O+

Question 21

What happens when hydrogen chloride is dissolved in organic solvents, such as methylbenzene?

Answer 21

It cannot ionise to form H+ and Cl-, and it stays as HCl.

Question 22

Why is HCl acidic in water but not in methylbenzene?

Answer 22

It cannot dissociate into H+ and Cl- ions (the H+ make it acidic) in the methylbenzene like it can in water and so it stays as HCl.

Question 23

What is a salt?

Answer 23

A substance that is formed when the hydrogen in an acid is replaced by a metal.

Question 24

What is the formula for hydrochloric acid?

Answer 24

HCl

Question 25

What is the formula for sulphuric acid?

Answer 25

H2SO4

Question 26

What is the formula for nitric acid?

Answer 26

HNO3

Question 27

What is the formula for phosphoric acid?

Answer 27

H3PO4

Question 28

What is the formula for ethanoic acid?

Answer 28

C2H4O3

Question 29

What is the test for hydrogen?

Answer 29

Holding a lighted splint near the gas and listening for a squeaky pop.

Question 30

What are the general rules for soluble salts?

Answer 30

* All nitrates * All sodium potassium, sodium and ammonium salts * Most chlorides (except AgCl, PbCl2, Hg2Cl2) * Group 1 carbonates are soluble (most are insoluble) * Most sulphates (except PbSO4, CaSO4, BaSO4) * Group 1 hydroxides + Ca(OH)2, Ba(OH)2 (most are insoluble)

Question 31

What are the solubility rules about nitrates?

Answer 31

All are soluble

Question 32

What are the solubility rules about sodium, potassium and ammonium salts?

Answer 32

All are soluble

Question 33

What are the solubility rules about chlorides?

Answer 33

Most are soluble except: | AgCl, PbCl2, Hg2Cl2

Question 34

What are the solubility rules about carbonates?

Answer 34

All group 1 are soluble. | Most are insoluble.

Question 35

What are the solubility rules about sulphates?

Answer 35

Most are soluble except: | PbSO4, CaSO4, BaSO4

Question 36

What are the solubility rules about hydroxides?

Answer 36

Group 1, Ca(OH)2 and Ba(OH)2 are soluble. | Most are insoluble.

Question 37

Describe the process of formation of an insoluble salt.

Answer 37

• Mix two solutions - one with the correct positive and one with the negative ion • Remember each of the first solutions must contain a soluble compound, or it can't be a solution • The reaction should form a solution and precipitate • Filter this to get the precipitate - this is the salt NO ACID REQUIRED

Question 38

What is the process of making an insoluble salt called?

Answer 38

A precipitation reaction

Question 39

Why can't sodium, potassium or ammonium salts be made using the 'adding an excess of solid and then filtering it off' method?

Answer 39

That method requires an insoluble base, and potassium, sodium and ammonium salts and compounds are always soluble.

Question 40

What method can be used to make a soluble salt which is not a sodium, potassium or ammonium?

Answer 40

• Get the correct metal oxide, carbonate or hydroxide, making sure it is insoluble • Get the correct acid • Keep adding the insoluble base to the acid until the reaction stops and there is an excess at the bottom of the acid • Filter off this excess, heat the remaining solution for some time and evaporate it to get crystals REQUIRES AN ACID

Question 41

How can you test for carbon dioxide?

Answer 41

Bubble through limewater, turns cloudy white

Question 42

How can you test for hydrogen?

Answer 42

Lighted splint would cause a squeaky pop