Chapter 8-Group 2, The Halogens and Quantative Analysis Flashcards
What is th common name given to group 2 metals?
Alkaline earth mentals
What is the trend in reactivity down group 2?
Reactivity increases down the group
What are three physical properties of group 2 metals?
- High melting and boiling points
- Low density metals
- Form colourless/white compoiunds
The highest energy electrons of group 2 metals are in which subsell?
S subshell
Why does reactivity increases down group 2?
The atoms in group 2 elements react by losing 2 electrons. Going down electrons are lost more easily due to the increase in shielding and atomic radius
What is the trend in the first ionisation energy going down group 2?
The first ionisation energy decreases because
- atomic radius increases
- nuclear attraction decreases
- shielding increases
What type of reaction is the reaction between group 2 elements and oxygen?
REDOX
What are the two products when group 2 elements react with water?
Hydroxide and hydrogen gas
Which group 2 element doesnt react with water?
Beryllium
What type of reaction is the reaction between a group 2 element and water?
REDOX
What is oxidised and what is reduced in a reaction between a group 2 element and water?
The metal is oxidised
One hydrogen atom from each water is reduced
What are the products when a group 2 element reacts with a dilute acid?
Salt and hydrogen gas
Write an equation for the reaction of calcium and hydrochloric acid
Ca (s) + 2HCl (aq) —> CaCl2 (s) +H2 (g)
What is formed when group 2 oxides react with water?
Metal hydroxide
Write an equation for the reaction between a group 2 oxide and water
MO (s) + H2O —> M(OH)2 (aq)
Which group 2 metal oxide is insoluble in water?
Beryllium oxide
What is the trend in hydroxide solubility down group 2?
Increases going down the group
Mg(OH)2 is slightly soluble
Be(OH)2 creates a strong alkaline solution
What is Ca(OH)2 used for? Include an equation
Its used to neutralise soil
Ca(OH)2 (aq) + 2HCl (aq) —> 2H2O (l) + CaCl2 (aq)
What is Mg(OH)2 used for?
Milk of magnesia is an antiacid used to treatt indigestion, heartburn etc.
This may be due to it slight solubility
What is calcium carbonate used for?
Found in limestone and marble which is used in the building industry
What is the drawback of using calcium carbonate in construstion? Include and equation
Group 2 carbonates react with acid
CaCO3 (s) + 2HCl (aq) —> CaCl2 (aq) + H2O (l) + CO2 (g)
What is the trend in melting point going down group 2 ? Why?
DECREASES
Due to ionic radius increasing and the electrostatic attraction between the nuclei and delocalised electrons decreasing
What is barium sulphate used for?
Used as barium meals for Xrays of the stomach and digestive system. This occurs because the barium atoms are heavy and good at absorbing Xrays. It can occur safely because barium has a poor solubility
What is the use of barium chloride?
Used to test for sulphate ions
1. Add an acid to remove any carbonate ions
2. Add barium chloride
If any sulphate ions are present a white ppt will form
List 2 properties of the halogens
- low melting and boiling points
- exist as diatomic molecules
What is the trend in boiling point going down group 7? Why?
As you go down group 7 molecules have more elctrons.
This menas that going down, london forces become stronger which are harder to break, so more energy is required.
Therefore boiling point INCREASES going down group 7
What is the trend in reactivity going down group 7? Why?
Reactivity DECREASES because,
Atomic radius increases
Electrons shielding increases
Nuclear attraction decreases
Electron affinity decreases
What is the trend in oxidising ability doing down gorup 7? Why?
Oxidising ability DECREASES
This is because Cl has the fewest occupied electron shells, the greatest force of attaction between the outer electrons and nucleus and therefore it is easiest to gain electrons and be reduced.
Oxidising agent-take an electron from a substance that has been oxidised
What is the trend in reducing ability going down group 7? Why?
Reducing ability INCREASES going down
This is because I- has the most occupied electron shells, so the outer electrons are further from the nucleus, there is a weaker force of attraction between the nucleus and outer electrons. Therefore it is the easiest to be oxidised and lose electrons- bets reducing agent
What is the colour of chlorine in water?
Pale green
What is the colour of bromine in water?
Orange
What is the colour of iodine in water?
Brown
What is the colour of chlorine in cyclohexane?
Pale green
What is the colour of bromine in cyclohexane?
Orange
What is the colour of iodine in cyclohexane?
Violet
Out of the three halides Cl-, Br- and I- which one can be oxidied by chlorine?
Br- and I- ions
Write the equation ofr chlorine oxidising bromide ions
Cl2 (aq) + 2I- (aq) —> 2Cl- (aq) + I2 (aq)
Out of the three halides Cl-, Br- and I- which one can be oxidised by bromine?
I- ions
Write the equation for bromine oxidising iodide ions
Br2 (aq) + 2I- (aq) —> 2Br- (aq) + I2 (aq)
Out of the three halides Cl-, Br- and I- which one can be oxidised by iodine?
None
Define disproportionation
The oxidation and reduction of the same elment in a redox reaction
What is the equation for the reaction of chlorine with water?
Cl2 (g) + H2O (l) —> HClO (aq) + HCl (aq)
What type of reaction is the reaction of chlorine with water?
Disproportionation
Chlorine is both oxidised and reduced simultaneously
Why is chlorine added to drinking water?
To kill the bacteria in the water (remove waterborne diseases) to make it safer to drink
What are the two forms of the chlorate ion?
ClO- is chlorate (I)
ClO3- is chlorate (V)
What is the equation for forming bleach?
Cl2 (aq) + 2NaOH (aq) —> NaCl (aq) + NaClO (aq) + H2O (l)
NaClO is bleach
What are the objections to chlrine being added to water?
- Chlorine is toxic when in excess
- Chlorine can react with hydrocarbons to form chlorinated hydrocarbons, some of which are carcinogens
What are anions also known as?
Negative ions
How can you test for carbonate ions?
- Add strong acid to the sample
- Collect the gas produced
- Pass through lime water
If positive fizzing will occur and lime water will turn cloudy
Write an equation for the carbonate test
CO ₃ 2- (aq) + 2H+ (aq) —> H ₂O (aq) +CO ₂ (g)
How can you test for sulphate ions?
- Add dilute hydrochloric acid
- Add barium chloride
If positive a white ppt will form
Write an equation for the sulphate test
Ba2+ (aq) + SO ₄2- (aq) —> BaSO ₄ (s)
What do you use to test for halide ions?
Acidified Silver nitrate, AgNO ₃
Why do you add HNO ₃ to test for halide ions and not HCl?
The HNO ₃ removes carbonate ions.
Adding HCL would add Cl- ions which would give a false positive result
How can you test for halide ions?
- Dissolve the sample in water
- Add aqueous silver nitrate
- Record the colour change
- If difficukt to distinguish the colour, add aqueous ammonia, first dilute ammonia then conc. ammonia
- Note the solubility of the precipitate
Write the result and equation for Cl- test
White precipitate, soluble in dilute aqueous ammonia
Ag+ (aq) + Cl- (aq) —> AgCl (s)
Write the result and equation for Br- test
Cream ppt, soluble in conc. aqueous ammonia only
Ag+ (aq) + Br- (aq) —> AgBr (s)
Write the result and equation for I- test
Yellow ppt, insoluble in conc. and dilute aqueous ammonia
Ag+ (aq) + I- (aq) —> AgI (s)
When testing for carbonate, sulphate and halide ions, which order should these tests be carried out and why?
- Carbonate test
- Sulphate test
- Halide test
They are tested in this order because barium ions form insoluble ppt of BaCO ₃ and silver ions form insoluble ppt of AgSo ₄
What are cations also known as?
Positive ions
How can you test for ammonium ions?
- Add sodium hydroxide to the same and warm gently
- Test the gas produced with red litmus paper
If positive the red litmus paper will turn blue and the ammonia will produce a pungent smell
Write the equation for the ammonium test
NH ₄+ (aq) + OH- (aq) —> NH ₃ (aq) + H ₂O (l)
