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4 Flashcards

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1
Q

Trends in Group 2:

Atomic radius

A

Atomic radius INCREASES as you go down the group

As you go down group, a full energy level of electrons are added between each element

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2
Q

Trends in Group 2:

1st Ionisation energy

A

1st ionisation energy DECREASES as you go down the group

All outer electrons are in a full s orbital

Shielding increases, so effective charge on nucleus decreases

This causes a decrease in the attraction to the outer electrons, therefore, less energy is needed to remove it

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3
Q

Trends in Group 2:

Melting/boiling points

A

Melting/boiling points DECREASES as you go down the group

All form 2+ ions in a metallic structure

Increased shielding causes weaker effective nuclear charge

This leads to a decrease in the strength of the electrostatic attractions with delocalised electrons

Therefore, less energy is needed to overcome them, so melting/boiling point is lower

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4
Q

Group 2 elements and water:

Reactivity of group 2 elements

A

Reactivity of group 2 elements INCREASES, as you go down the group

Group 2 metals are oxidised , as they lose 2 electrons when they react

Ionisation energies decrease as you go down the group, so the outer electrons are lost more easily

This is due to the increased shielding which causes a lower effective charge on the nucleus, therefore, they react more easily

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5
Q

Group 2 elements and water:

Magnesium and water

A

Mg (s) + H2O (g) —–> MgO (s) + H2 (g)

  • Heat/steam needed in order to react
  • Insoluble MgO formed.
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6
Q

Group 2 elements and water:

Cs/Sr/Ba and water

A

X (s) + 2H2O (l) ——-> X(OH)2 + H2 (g)

  • React with cold water
  • Basic metal hydroxide formed

Nb: Solubility of group 2 oxides increases down group, so state symbol varies

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7
Q

Reaction of Mg with oxygen

A

2Mg (s) + O2 (g) ——-> 2MgO (s)

Bright white flame

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8
Q

Reaction of Ca with oxygen

A

2Ca (s) + O2 (g) ——–> 2CaO (s)

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9
Q

Reaction of Sr with oxygen

A

2Sr (s) + O2 (g) ———> 2SrO (s)

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10
Q

Reaction of Ba with oxygen

A

2Ba (s) + O2 (g) ———> 2BaO (s)

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11
Q

Reaction of Mg with chlorine

A

Mg (s) + Cl2 (g) ———-> MgCl2 (s)

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12
Q

Reaction of Ca with chlorine

A

Ca (s) + Cl2 (g) ———-> CaCl2 (s)

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13
Q

Reaction of Sr with chlorine

A

Sr (s) + Cl2 (g) ———-> SrCl2 (s)

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14
Q

Reaction of Ba with chlorine

A

Ba (s) + Cl2 (g) ———-> BaCl2 (s)

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15
Q

Trend in solubility of group 2 hydroxides?

A

The solubility of group 2 INCREASES as you go down the group

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16
Q

Trend in solubility of group 2 hydroxides?

A

The solubility of group 2 hydroxides INCREASES as you go down the group

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17
Q

Trend in solubilty of group 2 sulfates

A

The solubility of group 2 sulfates DECREASES as you go down the group

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18
Q

Trend in solubility of group 2 sulfates

A

The solubility of group 2 sulfates DECREASES as you go down the group

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19
Q

Trend in solubility of group 2 carbonates

A

Group 2 carbonates are INSOLUBLE

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20
Q

Tests for group 2 salts

A

-Add Na2CO3 (aq) ——> White precipitate for ALL

-Add Na2SO4 (aq) ——–> MgSO4 = no ppt
BaSO4 = Thick ppt

-Add Na2OH (aq) ———> Mg(OH)2 = white ppt
Ba(OH)2 = No ppt

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21
Q

Thermal decomposition:

A

The use of heat to break down a reactant into multiple products

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22
Q

Thermal decomposition of carbonates

A

The positive ion causes heterolytic fission of the C—O- bond

The greater the charge density of the positive ion, the more readily this occurs

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23
Q

Thermal decomposition of Group 1 carbonates

A

Li2CO3 (s) ——-> Li2O (s) + CO2 (g)
Only Lithium carbonate (LiCO3) decomposes

Charge density in the other group 1 carbonates too low, and decomposition does not occur

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24
Q

Thermal decomposition of Group 2 carbonates

A

Thermal stability of group 2 carbonates INCREASES as you go down the group.

ie. they become more difficult to decompose as charge density DECREASES.

Therefore, the carbonate ion is less likely to be POLARISED.

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25
Q

Test for sulfate ions

A

Ba2+ ions test for sulfate ions and sulfate ions test for Ba2+

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26
Q

Thermal decomposition of Group 1 nitrates

A

Lithium:
4LiNO3 (s) ———> 2LiO (s) + 4NO2 (g) + O2 (g)

Rest of group 1 nitrates:
2XNO3 (s) ———–> 2XNO3 (s) + O2 (g)

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27
Q

Thermal decomposition of Group 2 nitrates

A

2X(NO3)2 (s) ——–> 2XO (s) + 4NO2 (g) + O2 (g)

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28
Q

NO2 (nitrate) observation

A

Brown gas

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29
Q

Trend in thermal decomposition of Group 2 nitrates

A

Thermal stability of group 2 nitrates INCREASES down the group

ie. they become more difficult to decompose as charge density DECREASES.

Therefore, the nitrate ion is less likely to be POLARISED.

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30
Q

How do we test the stability of carbonates?

A

One is to heat a known mass of carbonate in a side arm boiling tube and pass the gas produced through lime water.

Time for the first permanent cloudiness to appear in the limewater.

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31
Q

How do we test the stability of nitrates?

A

Measure length of time it takes until a specific amount of NO2 is produced.

NO2 is a brown gas that can easily be observed, but is toxic so must be done in a fume cupboard

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32
Q

How to carry out a flame test?

A
  1. Use a nichrome wire
  2. Sterilise the wire by dipping in concentrated hydrochloric acid and then heating in Bunsen flame
  3. Make sure the sample powdered or grinded
  4. Dip wire in solid and put in Bunsen flame and observe flame
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33
Q

Group 1 flame test colours:

A 
Li - red
Na - Yellow/orange
K - Lilac
Rb - Deep red
Cs - Violet
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34
Q

Group 2 flame test colours:

A

Mg - No colour
Ca - Orange/red
Sr - Red
Ba - Apple green

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35
Q

Explanation of the flame test colours

A

The heat causes the electron to get excited and be promoted to higher energy levels in the atoms

As they fall back down their ground state, they emit excess energy in the form of an electromagnetic wave

The further they fall, the higher the frequency emitted

Different frequencies = different colours

36
Q

Why does magnesium show no colour in a flame test

A

The frequency emitted by Mg may not fall in the visible light part of the spectrum

37
Q

Reaction of group 2 oxides with water

A

They are basic metal oxides, and react readily with water
Same equation for all, but magnesium hydroxide is solid, whereas rest are aqueous

Mg (s) + H20 (l) ——-> Mg(OH)2 (s)

X (s) + H20 (l) ——-> X(OH)2 (AQ)

38
Q

Reaction of group 2 oxides with dilute acids

A
  • Neutralisation reaction
  • Forms basic salt and water

MO (s) + HCl (l) ——-> MCl2 (aq) + H20 (l)

MO (s) + H2SO4 (l) ———> MSO4 + H20 (l)

39
Q

Why is the Mg(OH)2 formed from the reaction between MgO and H20 only PH9 but the other hydroxides formed are PH12?

A

Mg(OH)2 is not as alkaline as it is only slightly soluble in water, so fewer OH- (aq) ions in solution

40
Q

Note on group 2 sulfates

A

State symbol of MSO4 can be (s) or (aq).

Solubility of group 2 sulfates DECREASES down the group

41
Q

Reaction of group 2 hydroxides and acid

A

-They neutralise acids

M(OH)2 + 2HCl (l) ——–> MCl2 (aq) + 2H20 (l)

42
Q

Trend in melting/boiling points of the group 7 elements

A

Melting/boiling points INCREASE down the group

Halogens exist as non polar diatomic molecules

Weak induced dipole forces exists between the molecules (these are broken when melted or boiled)

Induced dipole forces become stronger as you go down the group as Mr increases. This is because more electrons are involved in the induced dipoles

43
Q

Trend in electronegativity of the group 7 elements

A

Electronegativity DECREASES down the group

Fluorine is the most electronegative as it has the greatest effective charge on the nucleus due to low shielding

This increases its ability to attract a bonding pair of electrons

44
Q

Testing for halide ions

A
  1. Acidified silver nitrate

2. Aqeuous ammonia

45
Q

Why is the silver nitrate acidified?

A

Nitric acid is added to test solution first to remove (neutralise) any CO3^2- or OH- impurities present

CO3^2- / OH- interfere with test because:

Ag2CO3 -white ppt
AgOH - brown ppt

46
Q

Results after adding acidified silver nitrate:

Fluoride ions

A

Ag+ (aq) + F- (aq) ——> AgF(aq)

No ppt

47
Q

Results after adding acidified silver nitrate:

Chloride ions

A

Ag+ (aq) + Cl- (aq) ——> AgCl (s)

White ppt

48
Q

Results after adding acidified silver nitrate:

Bromide ions

A

Ag+ (aq) + Br- (aq) ——> AgBr (s)

Cream ppt

49
Q

Results after adding acidified silver nitrate:

Iodide ions

A

Ag+ (aq) + I- (aq) ——> AgI (s)

Pale yellow ppt

50
Q

Results after adding aqueous ammonia:

Chloride ions

A

AgCl (s) dissolves in DILUTE NH3 (aq)

51
Q

Results after adding aqueous ammonia:

Bromide ions

A

AgBr (s) dissolves in CONC NH3 (aq)

52
Q

Results after adding aqueous ammonia:

Iodide ions

A

AgI (s) will NOT dissolve

53
Q

Reaction of chlorine and water

A

Water reacts with chlorine to form HCl and chloric acid

Cl2 + H20——–> HCl + HClO

It is a disproportionation reaction as chlorine is oxidised from 0 in Cl2 to +1 in HClO and reduced from 0 in Cl2 to -1 in HCl

HClO is antibacterial (oxidising agent), hence addition of chlorine to swimming pools and in water treatment

54
Q

Reaction of chlorine and water in the presence of UV light

A

In the presence of UV light, chlorine and water do not produce chloric acid

2Cl2 + 2H20 ——> 2HCl + O2

Occurs in the presence of UV light, so outdoor pools need chlorinating more often

55
Q

Reaction of chlorine and COLD DILUTE sodium hydroxide solution to form bleach

A

Chlorine reacts with COLD DILUTE sodium hydroxide solution to form sodium chloride, sodium chlorate (1) and water

Cl2 + 2NaOH ——–> NaCl + NaClO + H20

Chlorine is oxidised from 0 in Cl2 to +1 in NaClO and reduced to -1 in NaCl

ClO- ions are oxidising agents and the active ingredient in bleach

56
Q

Reaction of chlorine and HOT CONC sodium hydroxide solution to form bleach

A

Chlorine reacts with HOT CONC sodium hydroxide solution to form sodium chloride, sodium chlorate (5) and water

3Cl2 + 6NaOH ——–> 5NaCl + NaClO3 + 3H20

Chlorine is oxidised from 0 in Cl2 to +5 NaClO3 and reduced to -1 in 5NaCl

57
Q

What are halogens?

A

Halogens are oxidising agents

The oxidising power DECREASEs down the group, with fluorine being the strongest oxidising agent and iodine the weakest

This is because as you go down, the effective nuclear charge decreases due to the increase in shielding

58
Q

What are halides?

A

Halides are reducing agents

The reducing power INCREASES down a group with fluorine being the weakest reducing agent and iodine the strongest

This is because as you go down, the effective nuclear charge decreases due to the increase in shielding

59
Q

Displacement

A

redox reaction between a halogen and a halide

A stronger oxidising agent displaces a weaker oxidising agent

60
Q

Observation when chlorine is displaced

A

Pale green

61
Q

Observation when bromine is displaced

A

Brown

62
Q

Observation when iodine is displaced

A

Orange

63
Q

Test for sulfate ions

A

Acidified barium solution. Produces barium sulfate which is a thick white ppt

64
Q

Testing for group 1 ions

A

ALL are soluble

65
Q

Testing for group 2 nitrate ions

A

All are soluble

66
Q

Testing for group 2 hydroxide ions

A

Insoluble at top, soluble at bottom

67
Q

Testing for group 2 sulfate ions

A

Soluble at top, insoluble at bottom

68
Q

Testing for group 2 halide ions

A

All are soluble

69
Q

Testing for group 2 carbonate ions

A

All insoluble white ppts

70
Q

Reaction between Ag+ and OH- ions

A

Brown ppt

AgOH(s)

71
Q

Reaction between Ag+ and S04^2- ions

A

White ppt

Ag2SO4

72
Q

Reaction between Ag+ and CO3^2- ions

A

White ppt

Ag2CO3

73
Q

Reaction between Ag+ and NO3- ions

A

Soluble

74
Q

Reaction of halide ions and concentrated sulfuric acid:

Fluoride ions

A

NaF + H2SO4 ——–> No reaction

No redox

75
Q

Reaction of halide ions and concentrated sulfuric acid:

Chloride ions

A

NaCl + H2SO4 ——–>HCl + NaHSO4
Acid/ base reaction
No redox
HCl = steamy fumes

76
Q

Reaction of halide ions and concentrated sulfuric acid:

Bromide ions

A

NaBr + H2SO4 ——–> HBr + NaHSO4

2H+ + 2Br- + H2SO4 ——–> Br2 + SO2 + 2H2O
Redox - sulfur reduced from +6 to +4

77
Q

Reaction of halide ions and concentrated sulfuric acid:

Iodide ions

A

NaI + H2SO4 ——–> HI + NaHSO4

2H+ + I- + H2SO4 ——–> I2 + SO2 + 2H20

6H+ + 6I- + H2SO4 ——–> 3I2- + S + 4H20

8H+ + 8I- +H2SO4 ——–> 4I2- + H2S + 4H20

78
Q

Observations during reactions of sodium halides with conc sulfuric acid:
Hydrogen halides

A

HCl, HBr, HI

Steamy fumes

79
Q

Observations during reactions of sodium halides with conc sulfuric acid:

Bromine

A

Brown fumes

80
Q

Observations during reactions of sodium halides with conc sulfuric acid:

Iodine

A

Purple fumes

81
Q

Observations during reactions of sodium halides with conc sulfuric acid:

sulfur dioxide

A

colourless gas with choking smell

82
Q

Observations during reactions of sodium halides with conc sulfuric acid:
Sulfur

A

Yellow solid

83
Q

Observations during reactions of sodium halides with conc sulfuric acid:
Hydrogen sulphide

A

H2S

pungent gas with rotten egg smell

84
Q

Reactions of hydrogen halides with water

A

All readily dissolve in water

Hx (g) + H2O (l) ——–> H3O+ (aq) + X- (aq)

Classed as strong acids as so they fully disassociate to form H+ (aq). This increases the concentration of hydrogen ions, so creates an acidic solution

85
Q

Reactions of hydrogen halides with ammonia

A

All readily react with ammonia

Hx (g) + NH3 (g) ——–> NH4x (s)
solid salt produced but presents as white smoke

chemistry (13 decks)

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