6 Acid, alkali and salts

Question 1

What is an acid?

Answer 1

Proton donor

HCl dissociates (breaks apart) in water to give H⁺ ions

Question 2

What is a base?

Answer 2

A proton acceptor

Question 3

What is an alkali?

Answer 3

An alkali is a soluble base which dissociates in water making an OH^- ion

Example NaOH is a soluble base, it dissociates into Na⁺ and OH^- in water

Question 4

Name three common acids

Answer 4

Hydrochloric acid

HCl

Sulphuric acid

H₂SO₄

Nitric acid

HNO₃

Question 5

Name three common alkali.

Answer 5

sodium hydroxide

NaOH

Potassium hydroxide

KOH

Ammonium hydroxide

NH₄OH

Question 6

What is the chemical formula for hydrochloric acid?

Answer 6

HCl

Question 7

What is the chemical formula for sulphuric acid?

Answer 7

H₂SO₄

Question 8

What is the chemical formula for nitric acid?

Answer 8

HNO₃

Question 9

Complete the general equation

Acid + Alkali –>

Answer 9

Acid + Alkali –> Salt + Water

Question 10

Explain how an alkali can neutralise an acid.

Answer 10

You need to add an indicator such as phenolphthalein to a sample of the alkali. It will turn pink.

Add small drops of the acid using a pipette until one drop turn the solution from pink to colourless.

You now have equal numbers of H⁺ ions and OH^- ions making H₂O or water

Question 11

Name three bases

Answer 11

Copper oxide

CuO

Aluminium oxide

Al₂O₃

Copper hydroxide

Cu(OH)₂

Question 12

What is the chemical formula for carbonic acid?

Answer 12

H₂CO₃

Question 13

What colour is methyl orange in acid and alkali?

Answer 13

acid - red

alkali- yellow

Question 14

Finish the general equation

Acid + metal carbonate –>

Answer 14

Spot the carbonate!

Think neutralisation + carbon dioxide

Acid + metal carbonate –> Salt + water + carbon dioxide

Question 15

What colour is phenolphthalein in acid and alkali?

Answer 15

Acid - colourless

Alkali- pink

Question 16

What colour is litmus in acid and alkali?

Answer 16

Acid- red

Alkali- blue

Question 17

What colour is univeral indicator in strong acid, weak acid, neutral, weak alkali and strong alkali?

Answer 17

strong acid- red

weak acid- yellow

neutral- green

weak alkali- blue

strong alkali- purple

Question 18

Name a strong acid and strong alkali

Answer 18

strong acid- HCl - stomach acid pH 2

strong alkali - NaOH - pH 14

Question 19

Name a weak acid and alkali

Answer 19

weak acid - carbonic acid

weak alkali - ammonia

Question 20

Name a neutral substance

Answer 20

water- universal indicator turns green

Question 21

Finish the reaction

HCl + NaOH –>

Answer 21

This is an acid + alkali - think neutralisation!

Salt + water!

HCl + Na_OH_ –> NaCl + H₂O

Question 22

Finish the reaction

H₂SO₄ + KOH –>

Answer 22

This is an acid + alkali - think neutralisation

salt + water

remember a salt is metal/non-metal or cation/anion

H₂SO_{4 (aq)} + 2KOH_(aq) –> K₂SO_{4 (aq)} + 2H₂O _(l)

don’t forget to balance it!

Question 23

Finish the general reaction

Acid + base –>

Answer 23

acid + base –> salt + water

Question 24

How do you spot an acid from its chemical formulae?

Answer 24

All acids have a hydrogen atom at the front of the chemical formula

HCl

H₂SO₄

H₂CO₃

HNO₃

Question 25

How do you spot a base from its chemical formulae?

Answer 25

The chemical formula would end with an oxide, hydroxide

CuO

Mg(OH)₂

Question 26

What will the products be in this reaction?

HNO₃ + CuO –>

Answer 26

This is an acid + base- think neutralisation

salt + water

2HNO_3(aq) + CuO_(s) –> Cu(NO₃)_{2 (aq)} + H₂O_(l)

Think of your solubility rules to help figure out the state symbols

All oxides are insoluble except for Na, K or NH₄⁺ - therefore CuO (s)

All nitrate salts are soluble- therefore Cu(NO₃)₂ (aq)

Question 27

What will the products be?

HNO₃ + CaCO₃ –>

Answer 27

Spot the carbonate!

carbonate + acid - fizzing and carbon dioxide made!

2HNO_3(aq) + CaCO_{<strong>3</strong>(s)} –> Ca(NO₃)_2(aq) + H₂O_(l) + CO_{<strong>2</strong>(g)}

Ca(NO₃)₂ is soluble - all nitrates are soluble

CaCO₃ is insoluble- all carbonates are insoluble except for Na, K and NH₄+

Question 28

What are the products?

H₂SO₄ + MgCO₃ –>

Answer 28

Spot the carbonate + acid?

Think neutralisation with carbon dioxide

H₂SO_4(aq) + MgCO_3(s) –>MgSO_4(aq) + H₂O_(l) + CO_2(g)

MgCO₃ is insoluble

All Carbonates are insoluble except for Na, K and NH₄⁺

MgSO₄ is soluble (aq)

All sulfates are soluble except for Pb and Ba

Question 29

Complete the general equation

Metal + Acid –>

Answer 29

Think fizzing

Metal + acid –> salt + hydrogen

The metal must be more reactive than hydrogen in the reactivitiy series (copper, silver, gold and platinum will not react with acid)

Question 30

What products will form?

Mg + HCl –>

Answer 30

Think fizzing and spot the hydrogen in the acid- what is left is a salt

Mg_(s) +2 HCl_(aq) –> MgCl_2(aq) + H_2(g)

HCl is aqueous- all acids are aqueous

MgCl₂ is aqueous- all halides are soluble except for Pb & Ag

Question 31

Name the products

Ca + H₂SO₄ –>

Answer 31

Think fizzing and spot hydrogen

Ca(s) + H₂SO_4(aq) –>CaSO_4(aq) + H_2(g)

Hydrogen is diatomic- H₂

Question 32

Name all the diatomic elements

Answer 32

H₂ , N₂ , O₂, Cl₂, Br₂, I₂, F₂

Question 33

Name the three oxides formed when petrol is burnt in a car engine

Answer 33

Sulfur in fuel reacts with oxygen to form SO₂

Nitrogen in air reacts with oxygen to form NO₂

Carbon in fuel reacts with air to for CO₂

Question 34

State two environmental impact of acid rain?

Answer 34

Acid rain lowers the pH of lakes and streams and aquatic life dies

Acid rain leaches minerals from the soil and trees die

Question 35

The following forms in a car engine

Sulfur in fuel reacts with oxygen to form SO₂

Nitrogen in air reacts with oxygen to form NO₂

Carbon in fuel reacts with air to for CO₂

What happens with all these non-metal oxides dissolve in the rain?

Answer 35

Non-metal oxide form acidic solution in water- Acid rain

SO₂ –> H₂SO₄

NO₂ –> HNO₃

CO₂ –> H₂CO₃