3.1.2 Group 2 Flashcards
What are group 2 elements sometimes called
Why
The alkaline earth metals
Their oxides + hydroxides are alkaline
What block are group 2 metals in
What electrons are in their outer shell
S block
2s electrons in outer shell
When does group 2 atomic radius increase
Why
Going down the group
Each element has extra shell
What generally happens to melting points going down group
Why
What element is the exception
Why
Decrease
As as atoms get larger, the sea of delocalised electrons are further away from positive nuclei so strength of attraction gets smaller
Mg is exception
It’s lattice atom arrangement is different to other alkaline metals
What do group 2 elements do in all their reactions
Lose their 2 outer electrons to form doubly positively charged ions
What’s the 1st and 2nd IE Equations of any group 2 elememts
1st : M (g) -> M+ (g) + e-
2nd: M+(g) -> M2+ (g) + e-
Why does it get easier to remove the 2 outer electrons in reactions going down the group
As they get further away from the nucleus
What makes an element more reactive
The easier it is to remove electrons
What reactions occur when group 2 elements react with water
Redox
E.g of magnesium reacting with water
Calcium reacting with water
Mg(s) + 2H20(l) -> Mg(OH)2(aq) + H2(g)
Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g)
What does calcium produce when reacting with water
What’s this used for
Limewater (slaked lime)
Used to treat acidic soil by farmers
What does magnesium produce when it reacts with water
What’s this used for
Milk of magnesia
Used as an antacid to treat indigestion
What does magnesium reacts slowly and fast with
Reacts slowly with cold water
Reacts fast with steam
What do all of the alkaline metal hydroxides look like
All white solids
What is solubility of metal hydroxides like going down group 2
Solubilities increase
What’s the pH of the hydroxide like if it’s more soluble
More soluble, the more OH- is released and the pH is higher
How do you test for the sulfate ion
2 steps
Using BaCl2/Ba(NO3)2
- Acidity with dilute HNO3(aq)/dilute HCl (aq)
- Add Ba(NO3)2(aq)/BaCl2(aq)
What will form if the SO4 2- ion is present
What’s the equation
A white ppt of BaSO4
Ba2+(aq) + SO4 2-(aq) -> BaSO4(s)
What ions could interfere with the results of testing for sulfate ion, id it’s present
What’s the equation
CO3 2- ions would also produce a white pot with Ba2+
Ba2+(aq) + CO3 2-(aq) -> BaCO3(s)
Why is the acidifying step in place when testing for sulfate ions
To safeguard against CO3 2- ions interfering
Acid will destroy the carbonate ion by producing CO2 gas
What do group 2 metals form when they react with oxygen
Metal oxide
What charge is the metal and oxygen in reactions with oxygen
Metal is 2-
Oxygen is 2+
What does Mg burn with in oxygen
Brilliant white light
What occurs in reactions with oxygen (R+O)
Oxidation of metal
Reduction of oxygen
What reaction is when group 2 metals react with dilute acids
MASH
Metal + Acid -> Salt + Hydrogen
What happens to the metal and H+ in the acid in reactions with dilute acids
Metal oxidised from 0 -> +2
Acids reduced from +1 -> 0
What do group 2 metal oxides form when they react with water
Alkaline solutions of metal hydroxides
What metal only reacts very very slowly with water to form a metal hydroxide
Magnesium
What do reducing agents do
Donate/lose electrons
What are classed as reducing agents
Why
Halides
As they can lose electrons
General eq for halides acting as reducing agents
2X- -> X2 + 2e-
What’s the weakest reducing agent
Strongest oxidising agent
F- weakest reducing agent
F2 strongest oxidising agent
What’s the strongest reducing agent
Weakest oxidising agent
I- strongest reducing agent
I2 weakest oxidising agent
What’s the halide ion like going down a group
Halide ion increases in size so outer electrons are less strongly attracted by nucleus and so ions can lose electrons more readily
Also increased shielding
If a halogen is a strong oxidising agent what’s its halide like
Halide will be a weak reducing agent
How can some halide ions be precipitated (2)
- Acidification with dilute nitric acid HNO3(aq)
2. Addition of silver nitrate solution AgNO3(aq)
Why is HNO3 used to acidify the sample when testing for halide ions
As it removes cons that could effect the result
If fluorine is produced what precipitate is there
None
If chlorine is produced what precipitate is there
White
If bromine is produced what precipitate is there
Cream
If iodine is produced what precipitate is there
Yellow
How can halides be further distinguished
By dilute, then concentrated ammonia (NH3)
What solution does AgCl form when it dissolves with dilute ammonia solution
A colourless solution
AgBr dissolves in concentrated ammonia solution but what is it insoluble in
Dilute ammonia
Ionic Equations of testing for halide ions with chloride, bromide and iodide
Ag+(aq) + Cl-(aq) -> AgCl(s)
Ag+(aq) + Br-(aq) -> AgBr(s)
Ag+(aq) + I-(aq) -> AgI(s)
How would u know if NaOH is present
Pungent smell
Turns red litmus paper blue
What 2 things in the sample could affect the results as they react with AgNO3(aq)to produce white ppts
Soluble carbonates (CO3 2-) Hydroxides OH-
When chlorine dissolves in water what does it form
What’s the equation
A mixture of hydrochloric acid,HCl and chloric acid, HClO
Cl2(g) + H2O(l) HCl(aq) + HClO(aq)
What’s the process called when chlorine dissolves in water
what happens to the chlorine
Disproportionation
Chlorine has been simultaneously oxidised (lost electrons) and reduced (gained electrons)
What does the presence of Cl2 and an equilibrium make the solution look
What does addition of alkali (OH- ions) cause to happen
Pale green
Adds water pushing the equilibrium to the right causing the green to fade
What happens if addition of acid (H+ ions) occurs when chlorine water dissolves in water
The green intensifies and Cl2 has can be emitted which is TOXIC
What’s an advantage of Cl2 in drinking water and swimming pools despite its toxicity
It’s dissolved in water in low concentrations to kill any bacteria
What is chloric acid (HClO)
What does it also do
It’s an oxidant agent and a bleach
Kills bacteria
What happens to blue litmus paper when testing for chlorine water
Blue litmus paper turns red (due to HCl), followed by white
Why does litmus paper go white if chlorine waters present
As HClO is a bleach
As chlorine isn’t very soluble in water, what can it easily be lost by
Evaporation
What’s the active ingredient in household bleach as well as an oxidising agent
How is it produced
Sodium chlorate(l) (NaClO)
Produced when chlorine reacts with cold, dilute sodium hydroxide
What’s the equation for chlorine reacting with sodium hydroxide
What type of reaction is this
Cl2(g) + 2NaOH(aq) -> NaClO(aq) + NaCl(aq) + H2O(l)
Disproportionation of chlorine
What can chlorine in tap water react with and do
Can react with methane (CH4) decaying vegetation and forming chlorinated hydrocarbons that are suspected carcinogens
What could we get if we didn’t chlorinate water
E.g
Waterborne diseases e.g typhoid, cholera
What are 2 alternatives to using Cl2 that aren’t as good
Ozone (O3)
UV light
