Chapter 8 - Reactivity trends Flashcards
outer shell configuration of G2 elements?
s (^2)
- are in s block
ions formed by G2 elements?
2+ ions
- loss of S(^2) electrons in in redox reactons
G2: properties from Magnesium to Barium (not Bryllium)?
- High MP & BP
- low densities
- form colourless compounds
which G2 element has a lower BP than expected and why?
Mg bc of the way atoms pack toegther when metallically bonded
Trend in reducing ability of G2 elements (1st and 2nd IE)
- ⬇ G electrons are lost more readily
- NC ⬆, but AR & S also ⬆
- overall, outer 2e-s attracted less strongly
- ⬇ G, elements become stronger reducing agents
the type of bonding in G2 is?`
GIANT METALLIC BONDING`
why does MP decrease down G2 from Ca?
- as go down group
- all of G2 ‘lose’ the 2 outer e- to the sea of delocalised e-s
- AR and S inc
- Change in charge density
- electrostatic attraction from + ions for delocalised e- decreases, so less energy needed to break metallic bond
G2: change in charge density?
bc the AR inc and the charge is the same, the charge is spread over a larger ‘volume’
reactions of G2 with Oxygen equations (2)
- Ca + O2 -> 2CaO(s)
- Sr + O2 -> SrO(s)
- ONLY METALOXIDE IS FORMED!!
Metals are always ___ ions?
+
G2 oxides and hydroxides are?
bases
G2 oxides and hydroxies are neutralised by acids to form ?
salt + water
G2 oxide + acid equation
CaO + HCl -> CaCl2 + H20
- salt and hydrogen are formed
G2 elements react with water to form?
metal hydroxides with a pH between 10 -12
- mg hydroxide = pH 9
- CaOH2 = 10/11
CaO and water reaction?
CaO +H20 -> Ca(OH)2
G2 hydroxides dissolve in water to form ?
alkaline solutions, with a pH between 10-12
solubility ____ down G2
increases (of hydoxides)
- meaning pH increases, become more alkali
solubility of hydroxide equation>?
Mg(OH)2 -> Mg 2+ + 2OH -
general equation for G2 reactions?
M - 2e(^-) -> M 2+
Ca - e- -> Ca2+
- is like the 1st and 2nd IE
trends down G2 are:
- Reactivity inc
- AR inc
- IE dec
- Solubility of hydroxides inc
- pH of hydroxides increases
physical properties of the halogens:
- Chlorine - yellow/pale green gas at RTP
- Br2 - dark orange liquid at RTP
- I2 - grey solid at RTP
- F2 - colourless gas at RTP
Why don’t we keep F or As in college?
- F is v reactive, dangerous
- As - radioactive element
Bromine is used to test for?
- alkenes
iodone is used to test for?
starch
Down G7, Mp ?
inc
electron arrangement of halogens ?
p5
TREND IN MP &BP DOWN G7 EXPLAINED?
- down G , they increase
- induced dipole forces between molecules, broken during M&B
- Strength of these induced dipole inc down G as no. of e-s increases, more energy required to break them, higher Mp&BP
Colours of the Halogens - Chlorine?
- in water: pale/ yellow
in cyclohexane: yellow
Colours of the Halogens - Bromine?
- in water: orange
- in cyclohexane - darker orange
Colours of the Halogens - iodine?
- in water: dark red/ brown
- in cyclohexane: purple layer
Colours of the Halogens - fluorine?
- in water - colourless
- in cyclohexane - colourless
what do the colours show about the solubility of the halogens in the 2 solvents?
- the darker colours in cyclohexane show the halogens dissolve better in cyclohexane
- water is a polar solvent, water mols stick together due to strong H bonds
- cyclohexane has no permanent dipole so can form induced dipoles with halogen
(GCSE) a more reactive halogen will ____ a less reactive halogen from a halide compound?
displace
when halogens react with a solution, the halide solution formed will be….
- colourless but the halogen will be coloured
Chlorine, Bromine Ionic equation?
Cl2 + 2Br - -> 2CL - + Br2
use _____ ___ instead of displacement?
oxidising ability
explain the trend in reactivity down G7 in terms of oxidising ability?
- halogens at top are the best oxidising agents
- down G7, eventho NC ⬆, S ⬆, so AR⬆
- = less attration between nucleus and outer shell electron
- = more diff for nucelsut o attract the 1 e- needed
In an explaining trend in reactivity of G7 ques, always include
- oxidising agents
- overall, down the group, halogens have less attractive force on the incoming electron
what is a disproportionation reaction?
the same element is both oxidised and reduced
halogens have ______ ____?
disproportionation reactios
reaction of chlorine and water?
Cl2 + H20 -> HCl + HClO
- hydrochloric acid/ hydrogen chloride produced
- and chloric acid hydrogen chlorate (I)
Benefit of adding chlorine to water?
- hydrogen chlorate (I) is produced which will kill germs/b bacteria/ viruses
suggest a risk of adding chlorine to water?
- Cl2 in the envir forms chlorinated hydrocarbons with organic chemicals. These may cause cancer
(Disproportionation) reaction of chlorine with sodium hydroxide solution
Cl2 (g) + 2NaOH(aq) -> NaCl(aq) + NaClO(aq) + H2O
- Sodium Chlorate (I)
- sodium chloride
Chlorine and sodium hydroxide ionic equation?
Cl2 + 2OH -> Cl- + ClO- + H2O
sodium chlorate use?
- powerful oxidising agent that kills bacteria and acts as a bleach, removing colour
overall the increase and decrease in Ox no. must be
equal
- use ox no when equations diff to balance
colours of aqueous solutions of halide ions?
- F- = colourless
- Cl- = colourless
- Br- = colourless
- I- = colourless
- a chemical test is needed to identify the halide ions
testing for halides?
1 - add dilute nitric acid
2 - add silver nitrate
3 - add ammonia, dilute then conc to see if precipitate dissolves
identifying chloride ion?
- white precipitate forms - AgCl
- Ag+ (aq) + Cl-(aq) -> AgCl(s)
- dissolves in dilute ammonia
identifying Bromide ions?
- cream precipitate forms - AgBr
- dissolves in conc ammonia to form a colourless solution, not in dilute tho
identifying Iodide ions?
- yellow precipitate -AgI
- insoluble - doesn’t dissolve in both dilute & conc ammonia
when doing a test for halides on foods?
- ,make a SOLUTION by DISSOLVING food
- make clear by filtering
Boiling as water purification?
- is extremely effec in eliminating microbiological contaminants from the water
- removes: microrganisms
- doesn’t remove: heavy metals
+ = no cost involved, very effective in removing harmful organisms - = time consuming, smell and taste not improved
distillation as water purification?
- water is first heated to boiling, water vapour rises to a condenser where vapour is condensed, collected + stored. most contaminants remain behin din the liquid phase vessel
- = organics with BP < 100 cannot be remove effec and can become conc in the product H20
- requires large amounts of energy
Filtration as water purification?
- good for dealing with all types of water contaminants
removes: bacteria, cysts, some will eliminate chemicals, heavy metals, pesticides, virsuses - don’t remov: depends on type
+ = usually light, portable, quick and cost effective - = filters will eventually need to be replaced, flow rate may be slow
UV light as water purification?
- great for neutralising microbiological contaminants such as bacteria, viruses
- kills: microorganisms
- DR: chemicals, heavy metals, sediments, debris
+ = small + lightweight - = won’t remove sediment, odours, debris
Iodine crystals as water purification?
- relatively convenient, comes in a no. of forms
kills: bacteria, viruses
+ = light weight, easy to use - = 20-30 min delay b4 drinking, no safe for preg women, some tablets leave a strong after taste
purification tablets/ halogens as water purification?
- use chemicals to kill microbiological contaminants. The most comn tablets are made from CL, AG, Cl dioxide, iodine was BANNED
- kill: microorganisms
- DR: chemicals, pesticides, heavy metals, sediments
+ = small, lightweight, cheap, cost effective - = usually have foul taste, waiting time, still drink the chemicals and addetives
to avoid false positives?
the sequence of the tests should be perormed in is carbonate, sulfate, then halide. (Barium Carbonate and silver sulfate are both insoluble)
test for carbonates?
- add 1moldm-3 nitric acid
- cloudy
- salt + water + carbon dioxide formed
tests for sulphates?
- dilute nitric acid
- add barium chloride solution
- white precipitate of BaSO4 (s)
(Ba2+ + SO42-)
why do we test for carbonates 1st?
- CO2 + H20 -> H2CO3
carbon dioxide from air, reversible reaction - thfr, any sol may contain carbonate ions
- if carbonate present, false +
- nitric acid removes dissolved CO2 and carbonate ions
TEST FOR AMMONIUM ION: CATION?
- add 2cm3 of 1moldm-3 NaOH to a spatula of solid ammonium compound
- gently warm
- gas released turns red litmus paper blue
NH4+ +OH- -> NH3(g) + H2O - ammonia = alkali
qualitative test?
- presence not conc
- observed changes
which electrons are lost when G2 metals react?
outer shell s2 electrons to gain a noble gas configuration
why are G2 elements reducing agents?
they r very easily oxidised
G2 metal and water equation?
Mg +2H2O -> H2 + Mg(OH)2
- Mg so v slow reaction
- metal hydroxide and hydrogen gas formed
why does the pH of solutions increas ⬇ G2?
- ⬇ G, oxides react more readily with water
- giving more hydroxide ions in solution
what does the solubiity of g2 hydroxides do ⬇ G
increases
use of calcium hydroxide?
- neutralisation
- used in agriculture to neutalise acidic salts
- Ca is used as more soluble than Mg hydroxide, more alkaline, saves farmer money
- calcium hydroxide + nitric acid -> cal nitrate + water
use of Mg hydrox and calcium carbonate?
- as ‘antacids’
- treating indigestion
- alkali’s are corrosive, Mg hydrox is milder alkali so safer to take into our bodies, less soluble so doesn’t dissolve and go into blood - needed in stomach
- Mag hydrox + hydrochloric acid -> mag chloride + water
why is G2 know as the alkali earth metals?
- react with water to form alkali solutions
- earth - old term that comes from metals that aren’t very soluble and are heat resistant
RULE - nitrates?
- all nitrates and G1 compounds tend to be soluble
the more soluble the hydroxide, the less…
precipitate will form
G2 - what increases ⬇ G
- AR
- A no
- Solubility
- pH of hydroxides
- Reactivity/ reducing ability
- Density
G2 - what decreases ⬇ G ?
- 1st IE
- MP
- Electronegativity
- its not abt the masses that react,
its abt no. of moles
how to test for H2 gas?
squeaky pop test
reactions of Limewater - cloudy, then clear?
- cloudy - Ca Hydrox + CO2 -> CaCO3 + water
- CaCO3 is insoluble, white precipitate
clear = CaCO3 + H2O + CO2 -> Ca(HCO3)2 - soluble product
G2 elements physical properties?
- all G2 have similar physical properties
- relatively high MP & BP
- generally low density, light materials
- form white compounds
reaction of G2 with oxygen need to be ____ to start?
heated
- w/o heat slow reaction will occur
All G2 elements react with water except ?
- Beryllium
- others react to form hydroxides and H gas
all G2 react with dilute acids except?
Beryllium
why will a solution of these metal hydroxides be alkaline?
- they r soluble in water
- they will release Hydroxide ions
trend in reactivity of G2 sulphates?
- ⬇ G, solubility of sulphates decreases
Magnesium Hydroxide is also known as ?
milk of magnesia
why are G2 compounds used?
hydroxides, oxides, carbonates are basic, can neutralise acids
g2 metals can also be used in?
titanium extraction
Ca uses?
- building materials - limestone and marble used in construction - both contain cal carbonate
- buildings made of these will gradually erode as CaCo3 will react with acids in rainwater
Ba uses?
- Barium Meal
- Ba2+ poisounous to humans, but aren’t free to move
- so Ba sulf can be safely ingested
- helps with visualisation of soft tissue on X ray
- often used in GI tract imaging - identifies blockages ect
down G7 electronegativity ?
- decreases
- outer e held further away from nucleus
( F most elecronegative elemrnt)
advantages of the chlorination of water?
- sanitises water
- prevents spread of infection: espec: water bourne diseases like cholera
disadvantages of the chlorination of water?
- water is chlorinated before reaching the customer - potentially w/o their direct consent
- possible that cl would react with organic matter forming chlorinated hyrocarbons - thought to cause cancer
- chlorine is a toxic gas
Halogens/ halides
agents
- halogens = oxidising agents
- halide ions = reducing agents
down G7
haogen/ halides - agents
- ⬇ G, oxidising ability of halogens decreases
- ⬇ G, reducing power of halide ion increases
halides with water?
form colourless acidi solutions:
Hydrofluoric, hydrochloric, hydrobromic, hydroiodic acid ect…
carbonate test can also be done for?
hydrogen carbonate ions
suphate test?
barium sulfate formed
- insoluble
- so white precipitate
wat does adding nitric acid do?
- removes any soluble impurities, wich could interefre w results
- incl: carbonates - woulf form insoluble silver carbonate
- & hydroxides - would form silver hydroxide
why is the halide test not used on fluoride ions?
- silver fluoride IS soluble
order of tests? (G7)
- Carbonate
- Sulfate
- Halide
reason for test order?
- carbonate test must be done b4 sulfate as BaCO3 is insoluble and not easily distnguishabe from barium sulfate
- the sulfate test must be done b4 halide test as silver sulfate is insoluble and could be mistaken for a silver halide
halide test results?
- silver chloride: white
- silver bromide: cream
- silver iodide: yellow
(white ppl add chlorine to swimming pools)
