chap 8: acids and bases

Question 1

what is an acid?

Answer 1

it is a substance that dissociates in water to produce hydrogen ions, H+

Question 2

list 3 properties of acids

Answer 2

1. sour taste
2. produce ions when dissolved in water hence acids are able to conduct electricity (due to presence of mobile ions
3. turns blue litmus paper red

Question 3

what is the product of acid and reactive metals?

Answer 3

salt + hydrogen gas (H2)

Question 4

how to check if an acid + metal reaction has taken place?

Answer 4

effervescence observed and metal dissolves

Question 5

how to test for hydrogen gas?

Answer 5

use a lighted splint. in the presence of hydrogen gas, the lighted splint will extinguish with a ‘pop’ sound

Question 6

what are some unreactive metals?

Answer 6

lead, copper, silver, gold

Question 7

what are metals that are too reactive?

Answer 7

potassium, sodium, calcium

Question 8

what is the product of acid + base

Answer 8

salt + water (H2O)

Question 9

how to check if an acid reaction with base has occured?

Answer 9

solid base dissolves. resulting mixture feels warm to touch.

Question 10

what is the reaction, where water is the only product other than salt?

Answer 10

neutralisation

Question 11

what is the product of the reaction of acid with carbonates?

Answer 11

salt + carbon dioxide (CO2) + water (H2O)

Question 12

how to check if an acid + carbonate reaction has taken place?

Answer 12

effervescence observed and metal carbonate dissolves

Question 13

how to test for carbon dioxide gas?

Answer 13

bubble gas into limewater (calcium hydroxide). in the presence of carbon dioxide gas, white precipitate will be formed in the limewater. the white precipitate that forms is calcium carbonate.

Question 14

what does the strength of an acid refer to?

Answer 14

strength of an acid refers to the extent of dissociation / ionisation of the acid when dissolved in water

Question 15

what is a strong acid?

Answer 15

a strong acid is an acid that completely dissociates/ionises in water to give a high concentration of hydrogen (H+) ions.

Question 16

what is a weak acid?

Answer 16

a weak acid is an acid that partially dissociates/ionises in water to give a low concentration of hydrogen (H+) ions

Question 17

what does concentration refer to?

Answer 17

concentration refers to the amount of solute dissolved in 1 dm3 of water or solvent

Question 18

what does basicity of acids refer to?

Answer 18

basicity of acids refer to the maximum number if hydrogen ions that can be produced by the ionisation of one molecule of the acid when dissolved in water

Question 19

what is a base?

Answer 19

a base is any metal oxide or metal hydroxide. they contain either the oxide (O2-) or the hydroxide (OH-) ions

Question 20

what are the characteristics of bases?

Answer 20

most bases are insoluble in water
bases react with acids in a neutralisation reaction to give salt and water only

Question 21

what is an alkali?

Answer 21

an alkali is a soluble base that dissociates/ionises in water to produce hydroxide (OH-) ions

Question 22

what is a strong alkali?

Answer 22

a strong alkali is an alkali that completely ionises /dissociates in water to give a high concentration of hydroxide (OH-) ions

Question 23

what is a weak alkali?

Answer 23

a weak alkali is an alkali that partially ionises/dissociates in water to give a low concentration of hydroxide (OH-) ions

Question 24

what are some properties of alkalis?

Answer 24

• bitter taste
  -feel slippery and soapy
  -produces ions when dissolved in water hence alkalis are able to conduct electricity (presence of mobile ions)
  -turns red litmus paper blue

Question 25

what are the products of an acid + alkali reaction

Answer 25

salt + water (H2O)

Question 26

what are the products of an alkali +ammonium salt reaction?

Answer 26

salt + ammonia gas (NH3) + water (H2O)

Question 27

how to check if an alkali + ammonia salt reaction has taken place?

Answer 27

effervescence observed and pungent gas produces

Question 28

how to test for ammonia gas?

Answer 28

-use a piece of moist/damp red litmus paper -if ammonia gas is released, the moist/damp red litmus paper turns blue

Question 29

how does a pH scale work?

Answer 29

1-6: solution is acidic - concentration of H+ higher than concentration of OH- 7: solution is neutral - concentration of H+ ions equals to concentration of OH- 8-14: solution is alkaline - concentration of OH- higher than concentration of H+

Question 30

what are the type of indicators to measure pH?

Answer 30

1. methyl orange -red colour in acidic solution -changes colour from pH 3-5 -yellow colour in alkaline solution 2. screened methyl orange -violet in acidic solution -changes colour from pH 3-5 -green in alkaline solution 3. litmus -red colour in acidic solution -changes colour from pH 5-8 -blue colour in alkaline solution 4. thymolpthalein -colourless in acidic solution -changes colour from pH 9-10.5 -blue colour in alkaline solution 5. universal indicator 0-2: strong acid - red colour 3-6: weak acid - orange/yellow colour 7: neutral - green colour 8-10: weak alkali - blue colour 11-14: strong alkali - purple/violet colour

Question 31

what nutrients do plants need to grow?

Answer 31

Nitrogen, Potassium and Phosphorus

Question 32

what can cause the soil to be unsuitable for plant growth?

Answer 32

-too much fertiliser added -environmental pollution such as acid rain

Question 33

how is the pH of soil controlled?

Answer 33

chemicals are often added to the soil to adjust its pH. soil that is too acidic can be treated with bases such as slaked lime (calcium hydroxide). this process is known as “liming” the soil. adding too much slaked lime can result in the soil becoming too alkaline, which is unsuitable for plant growth ( cannot add sodium/potassium hydroxide —> too alkaline)

Question 34

how are oxides classified?

Answer 34

1. metallic oxides -basic oxides -amphoteric oxides 2. non-metallic oxides -neutral oxides -acidic oxides

Question 35

what are basic oxides?

Answer 35

-all metal oxides (except ZAP oxides) are basic oxides -most basic oxides are insoluble in water -basic oxides are solids at room temperature -they react with acids to form salt and water

Question 36

what are amphoteric oxides?

Answer 36

-zinc, aluminium and lead (ii) oxide -metallic oxides that react with both acids and bases to form salt and water -can act as both a basic oxide and/or an acidic oxide

Question 37

what are acidic oxides?

Answer 37

-most oxides of non-metals are acidic oxides -most acidic oxides dissolve in water to form acids - react with alkalis to form salt and water

Question 38

what are neutral oxides?

Answer 38

-H2O (water), CO (carbon monoxide), NO (nitrogen monoxide) -shows neither basic nor acidic properties -insoluble in water

Question 39

what are some strong acids?

Answer 39

HCl (hydrochloric acid), H2SO4 (sulfuric acid). HNO3 (nitric acid)

Question 40

what are some weak acids?

Answer 40

H3PO4 (phosphoric acid), CH3COOH (ethanoic acid), H2CO3 (carbonic acid)

Question 41

what are some weak acids?

Answer 41

H3PO4 (phosphoric acid), CH3COOH (ethanoic acid), H2CO3 (carbonic acid)