AS Inorganic Chemistry Flashcards
How is the periodic table arranged?
- by atomic number (proton number)
- periods (across/rows) = same number of electron shells
- groups (down/columns) = same number of electrons in their outer shells
How can the periodic table be used to work out electronic configuration?
Sally died painfully = SDP
Why does atomic radius decrease across a period?
- as the number of protons increases across the period the electrostatic attraction between the nucleus and outer shell electrons increases reducing the atomic radius
What how does melting point change across a period 3 for the first three metals?
- mp and be increases across the period because the metal-metal bonds get stronger
What is the melting point like from silicon?
- macromolecular with a tetrahedral structure = strong covalent bonds link all its atoms together so it has a high melting point
What is the trend in melting point across period 3 for P, S and Cl?
- all molecular substances
- their melting points depend on their van der waals
- sulphur has the most van der walls so has a higher melting point than p and cl
Why is argon’s melting point so low?
- it exists as individual atoms resulting in very weak van der waal forces
What is the trend ionisation energy across a period?
- increases across a period, due to the increasing attraction between the outer shell electrons and the nucleus due to the number of protons increasing
What is the trend in atomic radius down group 2?
Atomic radius increases down the group = as electron shells are added increasing the shielding and reducing strength of the electrostatic attraction between
What is the trend in first ionisation energy down group 2?
- each element down a group has an extra electron shell compared to the one above
- extra inner shells shield the outer electrons from the attraction of the nucleus
- making it easier to remove outer electrons
What is the trend in reactivity down group 2?
Reactivity increases down the group as group 2 elements lose 2 electrons forming positive ions. It is easier to lose electrons the more reactive the element
What is the trend in melting points down group 2?
Decreases down the group as more shielding means electrostatic attraction is weaker and it is easier to break the bonds
- magnesium is much lower because of its crystal structure
What happens when group 2 elements react with water?
When group 2 elements react they are oxidised from a state of 0 to +2
- group 2 metals react with water to from metal hydroxides and hydrogen
- they react more readily down the group because ionisation energies decrease
How does solubility in group 2 depend on the compound anion?
Group 2 elements that contain singly charged negative ions (e.g. OH-) increase in solubility down the group
Group 2 elements that contain doubly charged negative ions (e.g. SO42-) decrease in solubility down the group
Barium sulphate is said to be insoluble
What is the test for sulphate ions?
- add acidified barium chloride to a solution containing sulphate ions
- if a white precipitate is formed there are sulphate ions present
How are group 2 compounds used to neutralise acidity?
- calcium hydroxide (slaked lime) is used in agriculture to neutralise acid soils
- magnesium hydroxide is used in some indigestion tablets as an antacid
What is barium sulphate used in barium metals for?
- barium sulphate is opaque to x-rays = they wont pass through it but will pass through soft tissues
- a patient swallows the barium meal, barium sulphate coats the tissues making them show up on x-rays
Why is magnesium used in the extraction of titanium?
The main titanium ore, titanium(IV) oxide is first converted to titanium(IV) chloride by heating it with carbon in a steam of chlorine gas
Then the titanium chloride is purified by fractional distillation, before being reduced by magnesium in a furnace at 1000’C
How is calcium oxide and calcium carbonate used to remove sulphur dioxide?
Acidic sulphur dioxide can be removed from flue gases by reacting with an alkali = wet scrubbing
Powered calcium oxide and calcium carbonate can be used
A slurry is made by mixing the calcium oxide or calcium carbonate with water, which is then sprayed onto the flue gases, producing a solid waste product of calcium sulphite
What are the properties of the first 4 halogens?
F2 = gas and pale yellow
Cl2 = gas and green
Br2 = liquid and red-brown
I2 = solid and grey
Their boiling points increase down the group = increasing strength of van der waals forces as the size and mr increases
Electronegativity decreases down the group = increased shielding
Why do halogens displace less reactive halide ions from solution?
A halogen will displace a halide from solution if the halide is below it in the periodic table
- when the halogens react they gain an electron, they get less reactive down the group, less oxidising
- Br will displace Cl, I will displace Br and Cl
How do chlorine and sodium hydroxide make bleach?
Mix chlorine gas with cold, dilute, aqueous sodium hydroxide you get sodium chlorate(I) solution = bleach
2NaOH(aq) + Cl2(g) —> NaClO(aq) + NaCl(aq) + H2O(I)
How does chlorine kill bacteria in water?
Chlorine + water = disproportionation, end up with a mixture of chloride ions and chlorate(I) ions
Cl2(g) + H2O <=> 2H+(aq) + Cl-(aq) + ClO-(aq)
In sunlight = chlorine can decompose water to from chloride ions and oxygen
2Cl2(g) + 2H2O <=> 4H+(aq) + 4Cl-(aq) + O2(g)
Chlorate ions kill bacteria, so adding chlorine to water can make it safe to drink or swim in
What are benefits and drawbacks of using chlorine to treat water?
Pros:
- kills disease-causing microorganisms
- prevents reinfection
- prevents the growth of algae, bad toasters and smells
Cons:
- very harmful to respiratory system when inhaled
- liquid chlorine can cause chemical burns
What happens to the reducing power of halides down a group?
To reduce something the halide ion needs to lose an electron from its outer shell
As you go down the group the attraction gets weaker
- the ions get bigger, so the electrons are further away from the positive nucleus
- there are extra inner electron shells, so there’s a greater shielding effect
What is the reaction NaF with H2SO4?
NaF(s) + H2SO4(l) —> NaH2SO4(s) + HF(g) = misty fumes, HF not strong enough reducing agents so the reaction stops here
Not a redox reaction
What is the reaction of NaCl with H2SO4?
NaCl(s) + H2SO4(l) —> NaH2SO4(s) + HCl(g) = misty fumes, HCl not stone enough so reaction stops here
What are the reactions for NaBr with H2SO4?
NaBr(s) + H2SO4(l) —> NaH2SO4(s) + HBr(g) = misty fumes of hydrogen bromide gas
2HBr(g) + H2SO4(l) —> Br2(g) + SO2(g) + sH2O(l) = HBr is a stronger reducing agent then HCl and reacts with the H2SO4 in a redox reaction, reaction produces choking fumes of SO2 and orange fumes Br2
What are the reactions of NaI with H2SO4?
NaI(s) + H2SO4(l) —> NaHSO4(s) + HI(g) = same initial reaction giving HI gas
2HI(g) + H2SO4(l) —> I2(s) + SO2(g) + 2H2O(I) = HI then reduces H2SO4
6HI(g) + SO2(g) —> H2S(g) + 3I2(s) + 2H2O(l) = HI very strong reducing agent so it keeps reducing the SO2 to toxic H2S, resulting in solid iodine too
What is the silver nitrate test for halides?
Add dilute nitric acid to remove ions which might interfere with
Add few drops of silver nitrate solution AgNO3
A precipitate is formed
Ag+(aq) + X-(aq) —> AgX(s) Where X = F,Cl,Br,I
What are the colours of the precipitates formed in the silver nitrate test for the halides?
F- = no precipitate
Cl- = white precipitate
Br- = cream precipitate
I- = yellow precipitate
What are the solubilises of silver halide precipitates in ammonia?
Cl- = white ppt dissolves in dilute NH3
Br- = cream ppt dissolves in conc. NH3
I- = yellow ppt insoluble in conc. NH3
How can you use flame test to identify group 2 ions?
- dip a nichrome wire loop in concentrated HCl
- dip wire loop into unknown compound
- hold the loops in the clear blue part in the flame
- observe the colour change
Ca2+ = brick red
Sr2+ = red
Ba2+ = pale green
How can you identify group 2 metals using dilute sodium hydroxide?
Add NaOH drop wise to test tube containing the metal ion solution and observe the precipitation that forms
Keep adding the NaOH until it is in excess
Mg2+ = slight white ppt with OH- and white ppt with excess OH-
Ca2+ = slight white ppt with OH- and slight white ppt with excess OH-
Sr2+ = slight white ppt with OH- and slight white ppt with excess OH-
Ba2+ = no change with OH- and no change with excess OH-
How can you use red litmus paper to test for ammonium ions?
If ammonia is present it will turn damp red litmus paper, blue
If you add hydroxide ions to a solution containing ammonium ions they will react to produce ammonia gas and water and gently heat
How can you test for sulphates with HCl and Barium Chloride?
Add a little dilute HCl and Barium chloride solution
If a white precipitate of barium sulphate it means the original compound contained sulphate
How can you use a pH indicator to test for hydroxides?
Red litmus paper will turn blue of hydroxide ions are present
How can HCl help to detect carbonates?
- add dilute HCl, a solution contains carbonate ions will fizz
- because ions react with the hydrogen ions in the acid to give carbon dioxide
- carbon dioxide turns limewater cloudy
