Chapter 8 - Reactivity Trends

Question 1

What are group 2 metals called?

Answer 1

Alkaline earth metals

Question 2

What type of agent are group 2 metals known as?

Answer 2

Reducing agents

Question 3

How do group 2 metals work as reducing agents?

Answer 3

Each metal atom is oxidised, losing two electrons to form 2+ ions which causes another species to gain these electrons and so get reduced

Question 4

What is formed when a group 2 metal reacts with oxygen?

Answer 4

Metal oxide

Question 5

What is formed when a group 2 metal reacts with water?

Answer 5

Metal hydroxide + hydrogen gas

Question 6

What is formed when a group 2 metal reacts with dilute acids?

Answer 6

Salt + hydrogen gas

Question 7

Why does reactivity increase down group 2 metals?

Answer 7

• Atomic radius increases
• More inner shells so heleiding increases
• Nuclear attraction decreases so less energy to lose electrons
• Formation of 2+ ions requires input of two ionisation energies

Question 8

Ionisation energies ________ down group 2 elements

Answer 8

Decreases

Question 9

Group 2 elements become _________ reducing agents down the group

Answer 9

Stronger

Question 10

What happens when a group 2 oxide reacts with water?

Answer 10

Hydroxide ions released to form alkaline solutions of the metal hydroxide

Question 11

What is the equation for reaction between calcium oxide and water?

Answer 11

CaO_(s) + H2O_(l) -> Ca²⁺ _(aq) + 2OH^- _(aq)

Question 12

What is formed when a solution of calcium oxide reacting with water becomes saturated?

Answer 12

Calcium hydroxide precipitate
Ca(OH)₂

Question 13

Solubility of group 2 hydroxides _________ down the group so resulting solutions contain _________ OH- ions and are more _________. Which means pH _________

Answer 13

Increases
More
Alkaline
Increases

Question 14

Compare the solubilities of Mg(OH)₂ and Ba(OH)₂

Answer 14

Mg(OH)₂ very slightly souble in water -> low OH- concentration in solution so pH ~ 10
Ba(OH)₂ much more soluble in water -> greater OH- concentration in solution so pH ~ 13

Question 15

What are the uses of calcium hydroxide, Ca(OH)₂? Give equation

Answer 15

Agriculture - added to fields to increase pH of acidic soils by neutralising the acids in soil
Ca(OH)_{2 (s)} + 2H⁺ _(aq) -> Ca²⁺ _(aq) + 2H₂O _(l)

Question 16

What are the uses of magnesium hydroxide Mg(OH)₂? Give equation

Answer 16

Medicine - treatment for acid indigestion by neutralisation
Mg(OH)_{2 (s)} + 2HCl _(aq) -> MgCl_{2 (aq)} + 2H₂O _(l)

Question 17

What are the uses of calcium carbonates, CaCO₃? Give equation

Answer 17

Medicine - treatment for acid indigestion by neutralisation
CaCO_{3 (s)} + 2HCl _(aq) -> CaCl_{2 (aq)} + 2H₂O _(l) + CO_{2 (g)}

Question 18

Trend in boiling point of halogens down the group?

Answer 18

Increases

Question 19

Why does boiling point increase down group 7 halogens?

Answer 19

• More electrons
• Stronger London forces
• More energy required to break intermolecular forces

Question 20

What type of agent are group 7 halogens known as?

Answer 20

Oxidising agents

Question 21

How do group 7 halogens work as oxidising agents?

Answer 21

Each halogen atom is reduced, gaining one electron to form 1- ions which causes another species to lose this electron and so get oxidised

Question 22

What happens in a displacement reaction of halogens?

Answer 22

More reactive halogen displaces halide from solution

Question 23

Colours of Cl₂, Br₂ and I₂ solution in water?

Answer 23

Pale green
Orange
Brown

Question 24

Colours of Cl₂, Br₂ and I₂ solution in cyclohexane?

Answer 24

Pale green
Orange
Violet

Question 25

What can displace I-?

Answer 25

Chlorine and bromine

Question 26

What can displace Br-?

Answer 26

Chlorine

Question 27

What can displace Cl-?

Answer 27

Nothing

Question 28

More reactive halogen gets __________ (________ electrons)

Answer 28

Reduced Gains

Question 29

Explain why reactivity decreases down the group 7 halogens?

Answer 29

- Atomic radius increases - More inner shells so heleiding increases - Nuclear attraction decreases so harder to gain electron

Question 30

Halogens become _______ oxidising agents down the group

Answer 30

Weaker

Question 31

What is disproportionation?

Answer 31

Redox reaction in which the SAME element is both reduced and oxidised

Question 32

Give the equation for chlorine purifying water?

Answer 32

Cl₂ + H₂O -> HClO + HCl

Question 33

Why is chlorine reacting with cold, dilute aqueous sodium hydroxide a better bleach than reacting chlorine with water?

Answer 33

Chlorine has a low solubility in water, so reacting with NaOH allows for a larger concentration of chlorate ions which act as a bleach

Question 34

Give the equation for the reaction between chlorine with cold, dilute aqueous sodium hydroxide?

Answer 34

Cl₂ + 2NaOH -> NaClO + NaCl + H₂O

Question 35

Which ion acts as a bleach?

Answer 35

Chlorate (I) ions, ClO-

Question 36

What are the benefits and risks of using chlorine in water treatment?

Answer 36

Benefits - kills bacteria Risks - hazards of toxic chlorine gas and formation of chlorinated compounds

Question 37

How is the carbonate test is carried out?

Answer 37

Add dilute HNO₃ to solution being tested

Question 38

What is the positive result for a carbonate test?

Answer 38

Effervescence (bubbles) to indicate the release of a gas (CO₂)

Question 39

How can the gas of a positive carbonate test be tested?

Answer 39

Bubble through limewater, it will turn cloudy in the presence of CO₂

Question 40

Barium sulfate is ___________ in water

Answer 40

Insoluble

Question 41

How is sulfate test carried out?

Answer 41

Add Ba(NO₃)₂ to solution being tested

Question 42

What is a positive result for a sulfate test?

Answer 42

White precipitate

Question 43

How is halide test carried out?

Answer 43

Add AgNO_{3 (aq)} to aqueous solution of sample being tested

Question 44

What is the positive result of a halide test if CHLORINE is present?

Answer 44

**White** precipitate which is soluble in **dilute** NH_{3 (aq)}

Question 45

What is the positive result of a halide test if BROMINE is present?

Answer 45

**Cream** precipitate which is soluble in **concentrated** NH_{3 (aq)}

Question 46

What is the positive result of a halide test if IODINE is present?

Answer 46

**Yellow** precipitate which is **insoluble** in concentrated NH_{3 (aq)}

Question 47

Give the ionic equation for reaction of CHLORINE with AgNO₃?

Answer 47

Ag⁺ + Cl^- -> AgCl

Question 48

Give the ionic equation for reaction of BROMINE with AgNO₃?

Answer 48

Ag⁺ + Br^- -> AgBr

Question 49

Give the ionic equation for reaction of IODINE with AgNO₃?

Answer 49

Ag⁺ + I^- -> AgI

Question 50

What is the sequence of tests for anions?

Answer 50

1. Carbonate test 2. Sulfate test 3. Halide test

Question 51

Why is carbonate test carried out before the sulfate and halide test?

Answer 51

BaCO₃ and AgCO₃ are both insoluble in water and form precipitates so carbonate ions need to be removed first

Question 52

Why is sulfate test carried out before the halide test?

Answer 52

AgSO₄ is insoluble in water and will form a precipitate so sulfate ions need to be removed first

Question 53

In a mixture of ions why should HNO₃ be used in the carbonate test and not H₂SO₄ or HCl?

Answer 53

Would affect sulfate and halide test otherwise

Question 54

In a mixture of ions why should Ba(NO₃)₂ be used in the sulfate test and not BaCl₂?

Answer 54

Would affect halide test otherwise

Question 55

How is the test for ammonium ions, NH₄⁺ carried out?

Answer 55

Add NaOH to solution being tested and warm it

Question 56

What is the positive result from ammonium ion test?

Answer 56

Moist pH indicator paper will turn blue in the presence of ammonia gas

Question 57

Give the equation for the ammonium ion test?

Answer 57

NH₄⁺ + OH^- -> NH_{3 (g)} + H₂O _(l)