Group 2 And 7 Flashcards
Why are the group 2 metals placed in the s block?
-outermost/highest energy electron is in the s orbital
Why does melting point decrease down the group?
-ionic radius increases so ions become less charge dense
-weaker ESFA between cations and delocalised electrons
Why does reactivity increase down Group 2
-In chemical reactions group 2 metals lose 2 electrons
-extra energy level every time so shielding and atomic radius increase
-weaker ESFA between nucleus and outermost e- so more easily lost
What type of reaction is a group 2 metal with cold water?
-Redox
State the equation for a group 2 metal and cold water
M + 2H2O -> M(OH)2 + H2
What is magnesium hydroxide known as?
-milk of magnesia
-used in indigestion tablets to neutralise excess stomach acids
What is calcium hydroxide known as?
-slaked lime
-used to reduce the acidity of soil
Are group 2 reactions with steam more or less vigorous than those with cold water?
More
What type of reaction is a group 2 metal with steam?
-Redox
State the reaction of a group 2 metal with steam
M(s) + H2O (g) -> MO(s) + H2(g)
What colour are all the insoluble group 2 hydroxides?
White
The solubility of group 2 hydroxides…
Increase down the group
Mg(OH)2 is almost…
Insoluble and may be sold as a suspension in water
Ca(OH)2 is sparingly…
Soluble and may be sold in solution as limewater
What is the formula for limewater?
Ca(OH)2
What colour are the insoluble group 2 sulphates?
White
How does solubility of the group 2 sulphates change down the group?
Decrease
What is barium sulphate known as?
A barium meal
Why is it safe to ingest barium sulphate despite it being highly toxic?
Because it is so insoluble
What is barium meal used for?
To outline the gut in medical x rays
What else can barium sulphate be used for?
-to test the presence of sulphate ions in an unknown sample
Why is a solution acidified with nitric or hydrochloric acid before testing for sulphate ions?
-to get rid of any carbonate ions that may interfere with the experiment
-barium carbonate would be formed
What do you do after you acidify the solution to test for sulphate ions?
-add barium chloride
-if a white precipitate (BaSO4) forms that’s means sulphate ions are present
What is the ionic equation for barium and sulphate ions?
Ba2+ + SO42- -? BaSO4
What else can magnesium be used for?
-Production of titanium
How is titanium extracted?
-titanium ore is converted to titanium chloride which is then reduced to titanium by reaction w/ magnesium
State the equation for reduction of titanium chloride using magnesium
TiCl4 + 2Mg -> Ti + 2MgCL2
What can calcium oxide to be used for?
Flue gas desulfurisation
What type of reaction is CaO with SO2?
Acid-base
Before flue-gases are released into the atmosphere they are…
Scrubbed with calcium oxide
State the reaction of calcium oxide with sulfur dioxide?
CaO + SO2 -> CaSO3
What type of structure do halogens have?
Simple molecular structure
What is electronegativity?
The ability of an atom to withdraw e- density towards itself in a covalent bond
How does electronegativity change down the group?
-decreases
-extra energy level each time so shielding and atomic radius increase
-weaker ESFA between nuclear and bonding electrons
The combination of reagents required to test for halide ions is:
(I) dilute nitric acid
(II)silver nitrate (AgNO3)
What is the purpose of dilute nitric acid in the tests for halide ions?
-to get rid of impurities such as carbonate
-carbonate would cause fizzing
When are the precipitates formed in a test for halide ions using silver nitrate?
-When aqueous Ag+ reacts with an aqueous halide ion X- to form a solid silver halid, AgX
Ag+ + X- -> AgX(s)
What silver halide does not form a precipitate as it is soluble?
Silver Fluoride
AgF
What is the white silver halide precipitate?
AgCl
What is the cream silver halide precipitate?
AgBr
What is the yellow silver halide precipitate?
AgI
What is the only silver halide precipitate that dissolves in dilute ammonia
AgCl
What is the equation of the reaction with silver chloride and ammonia?
AgCl + 2NH3 -> [Ag(NH3)2]+ + Cl-
What is [Ag(NH3)2]+
-a silver complex present in toluene’s reagent
-silver ion with two ammonia molecules in a linear arrangement
-lone pairs on N atoms in the ammonia molecules form dative covalent bonds with silver ion in the centre
How do you differentiate between AgBr and AgI
-add concentrated ammonia
-AgBr dissolves and AgI doesn’t
What is the equation for the dissolving of AgBr?
AgBr (s) + 2NH3 -> [Ag(NH3)2] + Br-
What is the trend in solubility of the silver halide down the group?
-decreases down the group
What is oxidising power?
-ability to gain electrons
Do halides or halogens have oxidising power
Halogens
What is halogen displacement?
-when a more reactive halogen displaces a less reactive halogen from a solution of one of its salts
What happens when Cl2 reacts with KBr
-colourless to orange
(Cl2 is a pale green solution)
What colour change happens when Cl2 is added to Ki
Colourless to brown
What colour change happens when Br2 is added to potassium iodide?
-colourless to brown
(Br2 is an orange solution)
State the overall and ionic equation for Chlorine and potassium bromine
-Cl2 + 2Kbr -> 2KCl + Br2
-Cl2- + 2Br -> 2Cl- + Br2
What is the strongest oxidising agent?
Cl2 as it can displace Br2 and I2
How does oxidising power change down the group
Decreases
why does oxidising power change down the group?
X2 + 2e- -> 2x-
-extra energy level each time
- increase in atomic radius and shielding
-weaker ESFA between nucleus and incoming electron so its harder to gain a electron
How are relative oxidising or reducing powers of species quantified?
Using standard electrode potentials
The more positive the value on the SEP the more feasible the…
Reduction process is
What is the strongest oxidising agent?
F2
What is the weakest oxidising agent?
I2
What is the strongest reducing agent?
I-
What is the weakest reducing agent?
F-
What is reducing power?
-the ability to reduce
-ability to be oxidised
When we are looking at reducing power we look at the ease with which the following process occurs:
2X- -> X2 + 2e-
How does reducing power change down the group?
Increases
What happens where KCL is added to H2SO4
Observations:
-white fumes
-effervesence
HCl
What is the equation for KCl and H2SO4
H2SO4 + KCl -> KHSO4 + HCl
Is the reaction between sulphuric acid and potassium chloride redox?
No
-no change in oxidation state
‘Cl- will not reduce H2SO4’
This is an acid-base reaction
What happens when you add KBr to H2SO4
-White fumes (HBr)
-Effervesence (SO2) (choking gas)
-orange vapour (Br2)
How many equations are there for the reaction between KBr and H2SO4
2
-redox
-acid base
What is the acid base reaction between H2SO4 and KBr
H2SO4 + KBr -> KHSO4 + HBr
What does a reaction between H2SO4 and KBr produce?
HBr
Br2 (redox)
SO2 (redox)
Why is Br- and better reducing agent than Cl-?
As there is a redox reaction with conc H2SO4
What observations are there when KI is added to H2SO4
-effervesence (choking gas) (SO2)
-white fumes (HI)
-yellow solid (S)
-black solid (I2)
-rotten egg smell (H2S)
Whart is the Acid-base reaction when potassium iodide is added to sulphuric acid?
KI + H2SO4 -> KHSO4 + HI
Why do we know iodide is the most powerful reducing agent?
-I- can reduce S in H2SO4 from +6 down to +4 (in SO2,) 0 (in S) and -2 (in H2S)
Why does reducing power of the halides change down the group?
-ionic radius increases (extra energy level each time)
-shielding increases
-weaker ESFA between nucleus and outer e-
-e- lost more easily
What happens when Cl2 is bubbled into water?
-A pale green solution is formed
What is the equation for when chlorine is bubbled into water?
Cl2 + H2O <—> HCl + HClO
What is HClO?
Chloric (I) acid
What type of reaction is the reaction of Cl2 with H2O?
Disproportional reaction
What happens in a disproportionate reaction?
When one species is simultaneously oxidised and reduced
ClO- is a powerful…
Bleach
Where does the reaction of Cl2 with H2O take place?
-swimming pools and drinking water
-ClO- is an oxidising agent that kills bacteria
Why is chlorine still ok to treat water despite it being toxic?
-only used in small amounts
-health benefits outweigh the risk
Rewrite Cl2 + H2O <—> HCl + HClO
Cl2 + H2O <—> 2H+ + Cl- + ClO-
What happens to the yield of ClO- ions if acid (H+) is added?
Cl2 + H2O <–> 2H+ + Cl- + ClO-
-Le Chateliers principle
-Reaction works to remove added H+
-Backwards reaction favoured
-POE moves to left
-Yield of ClO- decreases
Using Le Chateliers principle, how would the system rep one if NaOH was added?
Cl2 + H2O <–> 2H+ + Cl- + ClO-
-When OH- is added, OH- reacts w/ H+ ions, removing them
-Reaction works to replace lost H+
-forwards reaction favoured
-POE moves to RHS
-yield of ClO- increases
Why is NaOH added to swimming pools?
-OH reacts with H+
-Forwards reaction favoured
-More ClO-
-More bacteria killed
What is the reaction that takes place when NaOH is added to chlorine?
Cl2 + 2NaOH -> NaCl + NaClO + H2O
What is the reaction of Cl2 with H2O in the presence of sunlight?
2Cl2 + 2H2O -> 4HCl + O2
Why do outdoor swimming pools require more frequent additions of chlorine
-Chlorine is lost from swimming pools
What is an alternative to the direct chlorination of swimming pools?
-Add sodium chlorate
-Dissolves in water to form chloric acid
NaClO + H2O -> NaOH + HCLO
Why do pools that are treated with Sodium Chlorate require a pH less than 7?
-H+ reacts with OH- (in NaOH) removing OH- reaction works to replace lost OH-
-forward reaction favoured
-P.o.E moves to RHS
-increased yield of HCLO (CLO- kills bacteria)
What is NaCLO?
Sodium Chlorate
