Chapter 8 Reactivity Trends Flashcards
What type of agents are group 2 elements ?
Reducing agents
- X—> X2+ +2e-
What three redox reactions do they undergo?
What are products
- with oxygen : gives you magnesium OXIDE
- with water : gives you magensium HYDROXIDE and HYDROGEN
- with dilute acids : gives SALT AND HYRDROGEN
Specific reaction of magensium with oxygen? (What observations?)
Burns with a brilliant white light
2) What is the trend of reactivity in general for the group 2 and how does work in water
It increases lower you go
- doesnt react with berrilium
- slowly with magnesium
- VIGOUROUS THE MORE YOU GO DOWN
In a redox reaction with water how does redox (in terms of numbers) work?
Hydrogen will reduce but some stay the same, others increase and thus oxidise
Why are group two elements more reactive down they go?
Why even thiugh other energy changes happen
What does this make them?
- to become 2+ ions from gaseous form requires the input of TWO IONISATION ENERGIES
- inionsstion energy lowers lower you go due to INCREASED SHIELDING and increased atomic radius, which both lower the overall nuclear attraction (and thus energy)
- EVEN THOUGH other energy changes take place when react the first /second ionisation male up most of the energy input
== this means they are stronger REDUCING AGENTS lower you go
In reaction of group 2 with water to make alkaline solution, what is the trend the lower you go?
Alkalinity + solubility increases
Why is grouo 2 more solubke / alklaine lower you go
Essentially last point
- The attraction between higher up metals is greater with the hydroxide ion (due to less shielding and less radius).
- as a result higher up there are less OH- ions aqeuos in the soltuion (more are still combined with the metal ).
- thus less alklaine higher and also less solible
Barium more alklaine and solible then magnesium due to HIGHER OH-(aq) CONCENTRATION!
How can the group 2 compounds be used as bases (3 different ones)?
A hydroxide
An oxide
A carbonate
How can group 2 compounds be used in agriculture (which compound)+ ionic equation
Calcium hydroxide Ca(OH)2 is added the acidic fields as LIME to increase pH of soil - white powder , neutrilises acid to water
Ca(OH)2 + 2H+—> H2O+ Ca2+
How can group 2 compounds be used in medicine?
Used as antacids fo neutrilse acid in stomach to cure acid indigestion
- these are either magnesium or calcium carbonates
- or magensium hydoxide which is suspended in water (slightly soluble ) as milk of magnesia
Reactions are :
Mg(Co3) + 2HCl—> MgCl2 + H2O + Co2
Mg(OH)2 + 2HCl—>MgCl2 + 2H2O
Why is milk of magnesia useful?
As it is only slightly soluble ots soluble enough to get to stomach but all that doesnt react can pass through your system as not soluble enough
Physical properties of group 2
How does boiling + melting change
- light
- compounds white or colourless
- high melting boiling but lower you go decrease
Finally what happens to groupn2 hydroxides when you hest
As only slightly soluble they become saturated and form a precipate like Ca(OH)2 lime
What do the halogens exist as lower down you go
Diatomic molecules, as gas and then solids as simole molecular
What is the trend in boiling point and why
Lower down you go = INCREASE
- this because the greater number of electrons cause greater and stronger number of london forced between and thus more energy needed to overcome so boiling point is higher
What is the appearance and state of all 5 halogens at RTP
Fluorine = pale yellow gas Chlorine = pale green gas (think dulce) Bromine = red brown liquid Iodine = shiny grey black SOLID astanine = never been seen but solid
What is the most common reaction, like group 2 metals, group 7 halogens take part in?
What are they referred to as
Redox reactions, hain electron and become reduced
As they make another species lose electrons they are OXIDISING AGENTS
How to test for alkalinity of group 2 hydoxides?ðŸ˜
Test water with it yiu should get dome thwt didnt react at end
Of different metals use different universal indicator and see pH, lower more alkaline and higher pH
How can we show the trend in reactivity fir these? What type of reaction?
Halogen- halid displacement reaction, here a more reactive halid will displace a less reactive one in redox reactions, kicking them out and thus changing colour of solution
What are the results of this test with chlorine everything?
Chlorine displaces all so in chlorine stays same = pale green pale green
In bromine kicks out so orange orange
In iodine kicks out so brown then purple /violet
Second is cyclohexane
Results for bromine with other halides?
Iodine
Bromine chrloine no reaction = pale green pale green
Bromine bromine no resction = orange orange
Bromine iodine iodine kicked = brown purple
Iodine chlorine no = pale green pale green
Iodine bromine = no = orange orange
Iodine iodine = no = brown purple
Why do we mix it with cyclohexane in halogen -halide displacements?
Cyclohexane or any other organic solvent that is NON POLAR is used ss halogens being non polar dissolve more readilly in cyclohexane than water (cuz polar polar).
Thus in cyclohexane it is easier to tell colours apart especially bromine and iodien which orange and brown can be confused with so orange orange and brown PURPLE
What is trend in reactivity lower you go and thus which is stringer oxidising agent
Lower go lower resctive, fluorine is the strongest oxidising agent
Why does reactivity decrease lower you go in group 7
Group 7 need to attract an electron to become a negative ion, but tendency to do this lower you go decreases
Lower you go the nuclear attraction decreases due to
- more shielding
-atomic radius
Thus harder to attract electron
And reactivity decrease
What is disproportionation reaction
What two reactions we lewrn
Where same element is both oxidised and reduced
1) chlorine with water
2) chlroine with cold dilute sodium hyroxide
Reaction of chlroine with water
How do product disenfect water?
What else does product act as?
How to test this —> what happens?
H20 + cl2 —> HClO + HCl
It is the chloric (I) acid that kills bacteria (their ions)
2) Chloric (I) acid also acts as a bleach
- test for this using blue litmus paper of chlorine with water
- due to their being two acids it becomes red
- but then due to chloric (I) acid being bleach it becomes white
Reaction disproportionation of chlroinenwith dilute cold aqueous sodium hyroxide
Why does chlorine react and dissolve more here compared to water
What use can you use product in
Cl2 (AQ) + 2NaOH (aq) —> NaClO(aq) + NaCl (aq) + H2O(l)
Chlroine rescts more with sodium hydroxide compared to water because not that soluble in water
This gives sodium chlorate where these ions uses in household bleach
Benefits and risks of chlorine use
Conlcusion
Benefit = disenfects water makes it safe to use and swim
Risk=
- toxic and large conc can kill
- in water can make way to decaying vegetation which produce methane and react with this. Chlorinated hydrocarbons increase cancer
However benefit of water outweighs this risk, water so importwnt
How to do carbonate anion test
What acid
What you di after (what id limewater) what is equation
What else can you do as substitiute
1) mix carbonate with NITRIC ACID = it will produce CO2 (salt and water)
2) bubble CO2 collected through limewater which is Aqueous soltition of Ca(OH)2 and a white precipatet of CaCO3 should be made and observed
Co2 + ca(OH)2 —> CaCO3 + H2O
See the effervescence
How to do sulfate test
What TO ADD IMPORTANT AND WHY
Modt sulfates are soluble in water except barium sulfste which is white
Add a few drops of HCL first to ensure no carbonate ions present or a white precipate woukd be made here too
Add barium NITRATE (not chloride cuz you gon do halide tesr after) to a sulfste compound.
- white precipate = barkum sukfste = positive for sulfate
How to do halide tests
Most halides solubke in water except silver halides which form coloured precipates
1) add aqueous silver nitrate to aqueos solution of a halide
2) milk cream butter
3) can confirm using aqueous ammonia to see which disolve ad a way to confirm ad some are close colours
Chlorine white and disolve in bith ammonia
Bromine cream and disolve in conc only
Iodine yellow and dont dissolve
What are ionic equations for halide test and sulfate
Ba2+ + So42- —> Ba2so4
Ag + + X- —> AgX
What order should you carry out test in
Why
Carbonate
Then sulfate
Then halide
Why?
Carbonate test is only test to produce bubbles so no fear of gettin wrong but
- in sulfate test barium nitrate can react to make barium carbonate which also forms white precipate so confusing. Need to do carbonate test first to ELLIMINATE OPTION
Then do halide test
- silver nitrate reacted with halides but it can reacr with both carbonate and sulfate to make white precipatets each. Thus do last once ELIMINATED OTHERS
How to do sequence of tests if trying to work out a MIXTURE OF IONS
Yiu need to do on same solution all three but follow steps
1) do carbonate test by continually adding HNo3 until stop bubbling. Here if there were any carbonate ions they wouldve turned into co2 and water so gone now.
- cant use sulfuric acid or HCl as this ruins other tesrs
2) do sulfate test by adding EXCESS barium nitrate in. If any sulfate this will go in amd become white barium sulfate. Now filter this out
- dont use BaCl2 again mess up next test
3) now you know all carbinate ion and sulfste gone no risk of silver these that give white precipatets
- do silver nitrate tedt
- CONFIRM WITH AMMONIA CONC TEST!
Finally how to do cation ammonium test ion
What equation + soltution needed
When heated together aqueous ammonium ions and hydroxide ions form AMMONIA AND WATER
NH4+ + OH- —> NH3 (g) + H20(l)
1) add aqeuous ammonia hydroxide to solution of ammonium ion
2) heat and the ammonia gas is released from being dissolved in water
3) hold DAMP RED LITMUS PAPER AND AS AMMONIA ALKALINE IT WILL TURN IT BLUE
Everything what
Nitrwte and aqueos
What to make sure mention abotu ammonia
CONC or not
Only alaklaine one
Ionic equations where possible
Confitions for ammonia to dissolve silver precipates?
Cold AND DILUTE
Why chlorinated hydrocabron bad
Carciongenic toxic positinus
What type of reactiin redox
Preicpwtiom
