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Chemistry > 8- Reactivity Trends > Flashcards

8- Reactivity Trends Flashcards

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1
Q

What is the outer shell electron configuration for Beryllium ions?

A

(Be2+) - [He]

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2
Q

What is the outer shell electron shell of Calcium ions?

A

(Ca2+) - [Ar]

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3
Q

How many electrons are in the outer shell of group 2 elements?

A

2

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4
Q

What happens when a Group 2 electron undergoes a redox reaction?

A

-metal atom is oxidised
-losses two electrons
-forms a 2+ ions (with electron configuration of a noble gas)
-group 2 metals are reducing agents (reduced another species)

Ca → Ca2+ 2e-

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5
Q

How do group 2 elements react with oxygen?

A

-form at metal oxide

2Mg + O2 → 2MgO

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6
Q

What are the changes in oxidation numbers when magnesium reacts with oxygen?

A

2Mg + O2 → 2MgO

Mg - starts with oxidation state of 0 and ends in +2
O- starts with oxidation state of 0 and ends in -2

Mg is oxidised
O2 is reduced

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7
Q

What is the reaction of the group 2 elements with water?

A

-form an alkaline hydroxide (general formula M(OH2) )
-form hydrogen gas

Sr + 2H2O ➝ Sr(OH)2 + H2

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8
Q

How does reactivity change down Group 2?

A

least reactive at the top (Beryllium)
most reactive at the bottom (Radium)

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9
Q

What is the reaction of group 2 elements with dilute acids?

A

-form a salt + hydrogen gas

metal+acid ➝ salt + hydrogen

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10
Q

What is the reaction between magnesium and dilute hydrochloric acid?

A

Mg + 2HCl ➝ MgCl2 + H2

Mg - goes through oxidation (goes from oxidation state of 0 to +2)
H- goes through reduction (oxidation state of +1 to 0)

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11
Q

Why does the first ionisation energies decrease down group 2?

A

The first ionisation energies decrease down the group because the attraction between the nucleus and the outer electrons decrease due to increased atomic radius and increased shielding

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12
Q

Why does reactivity increase down group 2?

A

-↑atomic radius ∴ increase in shielding
-decreased attraction between the outer electrons and the positive nucleus
-less energy is required to remove outer electrons

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13
Q

What happens when you react a carbonate with an acid?

A

carbonate + acid = salt + water + C02

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14
Q

What is the reaction like between Group 2 oxides and water?

A

-release hydroxide ions (OH-)
-form alkaline solutions of the metal hydroxides

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15
Q

Write an equation for the reaction between calcium oxide and water

A

CaO + H2O ➝ Ca2+ + 2OH-

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16
Q

Are group 2 hydroxides soluble in water?

A

-slightly
-when the solution becomes saturated, any further metal and hydroxide ions will for a solid precipitate
eg.

Ca2+ + 2OH- ➝ Ca(OH)2

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17
Q

How does the solubility of hydroxides change down group 2? And why?

A

-increases as you go down the group
-results in solutions containing more OH- ions are more alkaline
-solubility increases along with pH and alkalinity

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18
Q

How are Group 2 compounds used in agriculture?

A

-Calcium Hydroxide (Ca(OH)2)
-Added to fields as lime
-Increase the pH of acidic soils
-Neutralises the soil forming neutral water

Ca(OH)2 + 2H+ ➝ Ca2+ + 2H2O

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19
Q

How are Group 2 compounds used in medicine?

A

-used as antacids for treating acid indigestion
-magnesium and calcium carbonates as main ingredients
-milk of magnesia is a suspension of magnesium hydroxide (Mg(OH)2) in water
-because magnesium hydroxide is only slightly soluble in water
-acid in stomach is mainly HCl and a neutralisation reaction takes place

Mg(OH)2 + 2HCl ➝ MgCl2 + 2H20
CaCO3 + 2HCl ➝ CaCl2 + H20 + CO2

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20
Q

How do halogens exist?

A

-diatomic molecules at room temperature and pressure (Cl2, Br2)

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21
Q

What is the trend of boiling points of halogens?

A

-boiling point increases as you go down the group
-more electrons
-stronger london forces
-more energy required to break the intermolecular forces

22
Q

How many electrons do halogens have in there outer shell?

A

7

23
Q

What is the charge of a halide ion?

A

1-

24
Q

How do halogens react in a redox reaction?

A

-halogen atom is reduced
-gain one electron to form a 1- halide ion (electron configuration of nearest noble gas)
-oxidising agent (oxidised another species)

Cl2 + 2e- ➝ 2Cl-

25
Q

What happens in a reaction if a halogen is more reactive then the halide?

A

-halogen displaces halide
-colour change occurs

26
Q

What do displacement reactions between halogens and halides show?

A

-reactivity of halogens decrease down the group

27
Q

Due to I2 and Br2 being hard to tell apart in water what can happen to be able to tell them apart?

A

-organic non-polar solvent (cyclohexane) is added
-mixture shaken
-non-polar halogens dissolve more readily in cyclohexane
-colours much easier to tell apart

28
Q

What are the colours of Cl2, Br2 and I2 in water?

A

Chlorine - pale green
Bromine - orange
Iodine - brown

29
Q

What are the colours of Cl2, Br2 and I2 in water?

A

Chlorine - pale green
Bromine - orange
Iodine- violet

30
Q

What is the reaction between chlorine and Br-?

A

Cl2 + 2Br- ➝ 2Cl- + Br2

31
Q

What is the reaction between bromine and I- ions?

A

Br2 + 2I- ➝ 2Br- + I2

32
Q

What are the trends in reactivity of the halogens?

A

-reactivity decreases down the group
-atomic radius increases
-more inner shells so shielding increases
-less nucleus attraction to capture an electron from another species

33
Q

Which halogen is the strongest oxidising agent?

A

-fluorine
-gaining electrons from other species more readily than the other halogens

34
Q

What is a disproportionation reaction?

A

-a redox reaction in which the same element is both oxidised and reduced

35
Q

What is the reaction of chlorine with water like?

A

-Cl2 + H20 ➝ HClO + HCl
-disproportionation reaction

36
Q

How is the reaction of chlorine with water used?

A

-drinking water treatment

37
Q

What is the reaction of chlorine with cold, dilute aqueous sodium hydroxide? What is it used for?

A

-limited by the low solubility of chlorine in water
-water contains dissolved NaOH, much more chlorine dissolves
-disproportionation reaction

Cl2 + 2NaOH ➝ NaClO + NaCl + H2O

-results in a large concentration of ClO- ions from sodium chlorate
-use as household bleach

38
Q

What are the benefits and risks of chlorine use?

A

-ensures our water is fit to drink and bacteria are killed, no risk of diseases like typhoid,cholera

-extremely toxic gas
-respiratory irritant in small concentrations, large concentrations are fatal
-chlorine can react with organic hydrocarbons which are suspected of causing cancer

39
Q

What is the reaction between aqueous halide ions and aqueous silver ions?

A

Ag+ + X- ➝ AgX (aq)

X = aqueous soloution of any halide

40
Q

How do you preform the carbonate test?

A
  1. In a test tube, add dilute nitric acid to the solid or solution
  2. If you see bubbles the unknown gas could be a carbonate
  3. To prove gas is carbon dioxide, bubble the gas through limewater (aqueous calcium hydroxide) . If CO2 if present will make a white precipitate
41
Q

What is the reaction between sodium carbonate and nitric acid?

A

Na2CO3 + 2HNO3 ➝ 2NaNO3 + CO2 + H2O

42
Q

How do you perform the sulfate test?

A

-add a few drops of dilute HCL
-add a few drops of Barium Chloride
-positive result = white precipitate formed

43
Q

Write an equation for the sulphate ion test

A

Ba2+ + SO4 2- ➝ BaSO4

44
Q

How do you test for halide ions?

A
  1. Add aqueous silver nitrate , AgNO3
  2. Record the colour change
  3. If difficult to tell colours apart, add aqueous ammonia
  4. Note the solubility of the precipitate
45
Q

What is the equation and result for the Cl- test?

A

-white precipitate, soluble in dilute aqueous ammonia

Ag+(aq) + Cl-(aq) → AgCl(s)

46
Q

What is the equation and result for the Br- test?

A

-cream precipitate
-soluble in concentrated ammonia only

Ag+(aq) + Br-(aq) → AgBr(s)

47
Q

What is the equation and result for the I- test?

A

-yellow precipitate
-insoluble in concentrated and dilute aqueous ammonia

Ag+(aq) + I-(aq) → AgI(s)

48
Q

When testing for carbonate, sulfate and halide ions, in which order should you carry out the tests and why?

A
  1. Carbonate
  2. Sulfate
  3. Halide

Because barium ions forms insoluble precipitate of BaCO3 and silver ions form insoluble precipitate Ag2SO4

49
Q

How do you test fir ammonium ions, NH4+?

A
  1. add sodium hydroxide (NaOH) to the sample
  2. Warm the mixture
  3. Test the gas produced with red litmus paper
50
Q

What are the observations for positive ammonia test?

A

-litmus paper turns blue
-ammonia has a pungent smell

51
Q

Write an equation for the ammonia test?

A

NH4+ (aq) + OH- (aq) ➝ NH3 (aq) + H2O (aq)

Chemistry (16 decks)

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