reactivity Trends Flashcards
why are group 2 elements defined as ‘s’ block elements
the highest energy electron is found in an ‘s’ subshell
why does electronegativity decrease down the group
atomic radii increases, bonding electrons further from the nucleus , sheilding the nucleus is less able to attract these electrons
why does reactivity increase down the group
increased atomic radius , increased sheilding , which leads to decreased attraction between nucleus and outer shell electrons which means it can lose electrons easier
group 2 metal with water forms
Metal hydroxide + hydrogen
group 2 metal with oxygen
metal oxide
group 2 metal with dilute acid
metal acid and hydrogen
group 2 metals react ….. with oxygen
vigorously
what is the type of reaction that takes place when group 2 metal reacts with oxygen
redox reaction
what is produced when oxides react with water
metal hydroxide ( alkaline)
what are oxides and hydroxides of group 2 metals
bases
are the solid oxides and hydroxides soluble in acid
yes
what is the typical PH for a metal hydroxide
10-12
the group 2 hydroxides are only slightly ………… in water . when it becomes saturated any further metal and hydroxide ions will form a solid precipitate
soluble
solubility of the group 2 hydroxides
increases down the group
what happens to the ph as you go down group 2 and why
ph increases ( becomes more alkaline ) as conc of OH- ions increases as higher solubility so more alkaline
what is calcium hydroxide used for
used by farmers to neutralise acidic soils
what is magnesium hydroxide used for
indigestion remedies to neutralise excess stomach acid
what is calcium carbonate used for
neutralise stomach acid
how reactive are the halogens
the halogens are highly reactive
what do the halogens exist as
diatomic molecules
what melting points do the halogens have
they have low melting and boiling points
what happens to boiling points down the group and why
boiling points increase down the group because number of electrons increases which makes the london forces (induced dipole - dipole interactions ) between molecules stronger so more energy is needed to overcome them
what happens to the physical states down the group
gas - liquid - solid
what is the configuration of the halogens
(noble gas ) s2 p5
where is the highest energy electron
p sub shell
what happens to reactivity down the group and why
reactivity decreases down the group and oxidising power decreases because atomic radius increases as number of shells increases. electron sheilding increases , decrease nuclear attraction down the group and ability to gain an electron decreases.
why are the halogens strong oxidising agents
they gain electrons . oxidising power decreases down the group . therefore less reactive down the group
what happens to the halogens
the more reactive halogen will oxidise and displace a halide of the less reactive halogen . this is a displacement reaction
what is the defenition of a displacement reaction
is a reaction in which a more reactive element displaces a less reactive element from an aqueous solution of the latters ions
what colour is chlorine in water
pale green
what colour is chlorine in chlorohexane
pale green
what colour is bromine in water
orange
what colour is bromine with cyclohexane
orange
what colour is iodine with water
brown
what colour is iodine with cyclohexane
violet
why has asatine never been observed
because it is highly reactive
why are small amounts of chlorine added to drinking water
to kill bacteria. a mixture of two acids hydrochloric and chloric(I) is formed
what is the formula for chloric(I)
HCLO(aq)
what is the defenition for disproportionation
disproportionation is the oxidation and reduction of the same element in a redox reaction
How is household bleach formed
If you mix chlorine gas with cold , dilute aqueous sodium hydroxide you get sodium chlorate(1) solution , sodium chloride and water
What is the formula for household bleach
NACLO
What is the equation for household bleach forming
2NAOH + CL2 -> NACLO + NACL + H20
What are some uses of sodium chlorate(I) solution
Water treatment, bleach paper and textiles , cleaning
What are the benefits of chlorine use
-Typhoid and cholera might break out if chlorine is not used
-chlorine prevents the growth of algae eliminating bad smells and tastes and removes discolouration caused by organic compounds
-it kills disease causing microorganisms
-some chlorine remains in the water and prevents reinfection further down the supply
What are the risks of chlorine use
It is an extremely toxic gas and it is a respiratory irritant in small concentrations and large concentrations can be fatal .
Chlorine in drinking water can react with organic hydrocarbons eg methane and these chlorinated hydrocarbons are suspected of causing cancer
Additionally liquid chlorine on skin or eyes can cause chemical burns p
What are the risks of chlorine use
It is an extremely toxic gas and is a respiratory irritant in small concentrations and large concentrations can be fatal . Chlorine in drinking water can react with organic hydrocarbons eg methane and these chlorinated hydrocarbons are suspected of causing cancer additionally liquid chlorine on skin or eyes can cause chemical burns
What else can we use to treat water
Ozone (03) - a strong oxidising agent which makes it great at killing microorganisms. However it’s expensive to produce and it’s half life in water means that treatment isn’t permanent
Ultraviolet light - it kills microorganisms by damaging their DNA but it is ineffective in cloudy water and like ozone it won’t stop water being contaminated down the line
How do we tell apart the colours of the displaced halogens
To tell them apart we add organic , non polar solvent eg cyclohexane and shake the mixture. The non polar halogen molecules dissolve more readily in organic solvents than in water .
What are the phases in the tubes
The lower phase is the aqueos phase (water) and the upper the organic phase (hexane)
What colour is chlorine water and potassium chloride before and after cyclohexane
Pale Green and pale Green
What colour is chlorine water and potassium bromide before and after cyclohexane
Yellow and orange
What colour is chlorine water and potassium iodide before and after cyclohexane
Orange/brown and purple
What colour is bromine water and potassium chloride before and after cyclohexane
Yellow and orange
What Is the colour of bromine water and potassium bromide before and after cyclohexane
Yellow and orange
What is the colour of potassium iodide and bromine water Before and after cyclohexane
Orange/brown and purple
What is the colour of iodine water and potassium chloride before and after cyclohexane
Orange/ brown and purple
What is the colour of iodine water and potassium bromide before and after cyclohexane
Orange/ brown and purple
What is the colour of iodine water and potassium iodide before and after cyclohexane
Orange/brown and purple
what substance is used to test for halide ions
silver nitrate solution is used to test for halides
describe the test for halide ions
first you add dilute nitric acid to remove ions that might interfere with the test, the colour of the precipitate identifies the halide then we add ammonia as each halide has a different solubility in ammonia. ( the larger the ion the more difficult to dissolve)
what is the general ionic equation for silver nitrate and halide ion
Ag+ + X- -> AgX
what colour is chloride
white precipitate
what colour is bromide
cream precipitate
what colour is iodide
yellow precipitate
what does chloride dissolve in
dilute ammonia ( NH3)
what does bromide dissolve in
concentrated NH3
what does iodide dissolve in
insoluble in conc or dilute nh3
What are qualitative tests for ions
They rely on observations , not measurements .
What do we look for in qualitative tests for ions
Gas bubbles , precipitate appearance , colour changes or identification of gases
How do you test for carbonate ions ( co3 2-)
Add dilute acid ( eg HCl) and if carbonate ions are present fizzing will occur and co2 is produced. If the evolved gas is co2 it will form a milky / cloudy precipitate when bubbled through limewater .
What is the ionic equation for carbonate ions test
( 2H+ + CO32- —> CO2 + H20) with acid. (CO2 + Ca2+ + 2OH- —> caco3 + h20) with limewater
How do you test for sulphate ions (SO42-)
Add dilute acid followed by a solution of barium ions ( eg barium chloride solution ) and a white precipitate of barium sulphate forms . Most sulphates are soluble in water but barium sulphate is insoluble
Why is it important that you do the carbonate test before the sulphate test
Barium carbonate and barium sulphite are also white precipitates so only do the sulphate test if sure not carbonate is present
What is the issue with using barium chloride solution to test for sulphate ions
You cannot then use the same sample to test for halide ions (chlorine present ) therefore we should use barium nitrate
How do we remove carbonate ions
Keep adding dilute acid until no more effervescence
What is the benefit of using nitric acid
The benefit of using nitric acid is that we can then go on and test the same sample for sulphate ions and halide ions (after testing for carbonate ) . If we used sulfuric acid to test for carbonate we cannot then use this sample to test for sulphate ions ( sulfuric acid contains sulphate ions ) additionally hydrochloric acid cannot be used to test for halide ions ( chlorine present )
What is the test for ammonium ions (NH4+)
Add sodium hydroxide solution and gently warm . A gas that has a choking smell is evolved , this gas will turn damp red litmus paper blue
Why do you heat the solution when testing for ammonium ions
It will not produce fizzing as ammonia gas is highly soluble in water and immediately goes into solution . However if we warm our solution then the ammonia is released from solution back to a gas
How does the ammonia turn the litmus paper blue
It is alkaline and it dissolves in the water in the damp paper
What is the sequence we have to test in if we want to do all three tests ( carbonate , sulphate and halide)
Carbonate test : if bubbles obtained keep adding acid until bubbling stops . This will have removed all carbonate ions . Nitric acid is used so no chloride or sulphate ions are introduced .
Sulphate test: now add an excess of barium nitrate . Filter to remove barium sulphate
Don’t use barium chloride as has halide ions
Halide test :
Any carbonate and sulphate ions will have been removed so any precipitate must be halide .
What is an equation to prove ammonia is an alkali
NH3 + H20 —> NH4+ + OH- ( alkali as OH- ions produced )
Why do we need to test for sulphate ions before we test for halide ions
Sulphate ions also produce a precipitate with silver nitrate causing a false positive
What is the reaction between calcium carbonate to form calcium oxide
Thermal decomposition caco3 with heat —> cao + co2
What happens to the melting points down group 2
Melting points decrease down the group . The metallic bonding weakens as atomic size increases , this is because the distance between the positive ions and delocalised electrons increases , therefore the electrostatic attractive forces between the cations and delocalised electrons increases weaken
Carbon dioxide and limewater equation
Ca(OH)2 + CO2 ——> CaCO3 + H20
What happens to the reactions with group 2 metals and heat down the group
The solutions heat up down the group
Magnesium and steam
Mg + h20 (g) —> mago + h2
Why do you need to use emery paper before doing a reaction with mg and oxygen
Mg will slowly react with oxygen without a flame . Mg ribbon will often have a thin layer of magnesium oxide in it this needs to be cleaned off by emery paper before doing reactions as if we are measuring reaction rates with mg and acid for example an uncleared mg ribbon would give a false result because both the mg and mgo would react at different rates
How come magnesium hydroxide is safe to use to neutralise stomach acid
Because it is very weakly alkaline
Mg burns with oxygen to produce a what flame
White flame
Why is there no reaction with sodium bromide and iodine but a reaction with chlorine and sodium bromide
Because iodine is a weaker oxidising agent than chlorine and therefore cannot displace sodium bromide
