Unit 2: Section 2- Group 2 and Group 7 Elements + RP4 Flashcards
What are group 2 known as?
The alkaline earth metals
How many electrons do group 2 elements have in their outer shell?
2
Name three trends that happen as you go down group 2
- Increasing atomic radius
- Decreasing first ionization energy
- Decreasing melting points
Explain the change in atomic radius as you go down group 2
Atomic radius increases as you go down group 2, as the number of shells increases by one as you go down group 2. This increases the distance and shielding between the outer electrons and the nucleus, decreasing the electrostatic attraction between them.
Explain the change in first ionization energy going down group 2
First ionization energy decreases down the group because the outermost electrons are further away from the nucleus, so less energy required for an electron to be removed. There is also an increase in shielding down the group, which decreases the attraction of the outer electron to the nucleus
Explain the change in melting point down group 2
Melting point decreases down the group because the metallic bonds become weaker as the size of the atoms increase. The greater the distance between the delocalized electrons and positive ions, the weaker the electrostatic forces of attraction
What forms when you react a group 2 metal with oxygen?
it forms a metal oxide
What is the general equation for group 2 metals reacting with oxygen?
2M + O2 –> 2MO
What is a useful property of magnesium?
It is very easy to ignite
What flame does magnesium burn with?
bright white flame
What happens when magnesium is ignited?
bright white flame
formation of a white powder
What happens to the magnesium when it is oxidized without being ignited?
Without a flame this reaction happens very slowly. The MgO in this case is formed as a thin layer that covers the surface of the magnesium.
What must happen to Mg if a thin layer of MgO has formed if the metal is to be used in electrolysis?
It must be rubbed down with emery paper to remove this oxide layer.
How does most of group 2 react with water?
very vigorously
What is the general equation for group 2 metals reacting with water?
M + H2O –> M(OH)2 + H2
forms metal hydroxide and hydrogen gas
What happens to metal hydroxides that are soluble?
They stay in solution, so an alkaline aqueous solution is formed in the reaction
How reactive is magnesium compared to the rest of group 2?
Magnesium is the least reactive of the group 2 metals
What is the only thing that magnesium will react with?
Magnesium will only react with warm water
What is the chemical reaction with Mg and warm water, also describe it
Mg (s) + 2H2O (l) –> Mg(OH)2 (aq) + H2 (g)
- tame reaction
- doesn’t produce a flame
What happens if magnesium reacts with steam?
If magnesium reacts with steam, it forms magnesium oxide and hydrogen.
This reaction does produce a flame, with magnesium burning with a bright white colour:
What is the only element in group 2 that does not react with water?
Beryllium
What observations could you observe from reactions of group 2 metals with water? (6)
- increase in temp
- metal dissolving
- melting of the metal into a ball
- metal moving around surface of water
- ignition of the metal, burning with a colored flame
- effervescence (hydrogen gas)
What happens to the reactivity of the metals as you go down group 2?
it increases
As the metals become more reactive, the reactions become more explosive.
How can titanium be extracted?
It can be extracted from its ores using the Group 2 metal magnesium
Name some uses/properties of titanium (2+3)
- used in aircrafts and
- in hip replacements
for its resistance to
- corrosion,
- abundance
- low density.
Why is titanium so expensive? (4)
- high temperatures are needed in the extraction
- The extraction process also requires an argon environment which is expensive.
- Magnesium is also required for extraction, which is expensive
- Extracting titanium is a batch process, which means that a lot of labour is required and energy is lost whenever the process stops.
Why cant titanium be extracted using carbon?
It would lead to the production of titanium carbide instead of titanium metal.
Why cant titanium be extracted via electrolysis?
It is not reactive enough
List the three steps of extracting titanium using magnesium
- solid titanium oxide is converted to liquid titanium chloride
- the liquid titanium chloride is then purified by fractional distillation
- magnesium is added to the liquid titanium chloride to extract solid titanium. As magnesium is more reactive than titanium, it will displace it in the salt to form magnesium chloride
What temperature is solid titanium chloride converted to liquid titanium chloride at and why?
9000 C
Done for purification as TiCl4 is liquid at room temperature
What is the reaction for the extraction of titanium using magnesium?
TiCl4 (l) + 2Mg (s) → Ti (s) + 2MgCl2 (l)
What do group 2 metals form when reacting with water?
Metal hydroxides
What happens to solubility as you go down group 2?
solubility increases
Why does solubility increase as you go down group 2?
Because there is an increasing radius of the metal cations
How does ions being similar in size effect electrostatic attraction?
Ions that are similar in size will experience stronger electrostatic attractions to one another as they are able to get closer together
Why does the metal cation being small effect the solubility of hydroxides ionic compounds?
As the hydroxide ion is quite small, smaller metal cations will create stronger, and so less soluble ionic compounds.
What happens if you dissolve a group 2 metal in solution?
when dissolved in solution they will form alkaline solutions, with the alkalinity of the solutions increasing down the group as solubility increases
Why is magnesium hydroxide considered to be ‘sparingly’ soluble?
Though magnesium hydroxide is considered insoluble in water, in a solution of magnesium hydroxide and water, the solution will become slightly alkaline. This solution will be about pH 9, meaning that some hydroxide ions are present.
Describe how magnesium hydroxides can be used in medications
Magnesium hydroxides lack of solubility makes it ideal for use in anti-acid medications. Usually taken in the form of a chewable tablet, Mg(OH) reaches the stomach as a solid, where upon it neutralizes with excess stomach acid.
What pH solution does calcium hydroxide produce with water?
Calcium hydroxide is partially soluble in water, producing an alkaline solution (pH 11).
What is another name for limewater?
aqueous calcium hydroxide
What can be used to test for carbon dioxide?
limewater
What happens in a positive test for carbon dioxide?
Aqueous solutions of calcium hydroxide (limewater) can be used to test for carbon dioxide. In this test, CO2 is bubbled through limewater causing calcium carbonate to be formed which presents as a white precipitate
What is the equation for a positive test for carbon dioxide?
Ca(OH)2 (aq) + CO2 (g) →CaCO3 (s) + H2O (l)
What is calcium carbonate used in the removal of?
used in the the removal of sulfur dioxide from flue gasses.
A slurry of CaCO3 is sprayed into the gasses and reacts reacts with acidic sulfur dioxide to produce solid calcium sulfite.
What can calcium hydroxide be used for?
Calcium hydroxide is also used in agriculture to maintain soil quality. When soil becomes too acidic for a crop, Ca(OH)2 can be added to increase its pH
What is barium hydroxides solubility in water?
barium hydroxide is very soluble in water. this means that a solution of barium hydroxide and water is very strongly alkaline
What do the group 2 metals form when they are reacted with sulfuric acids?
metal sulfates
What trend does the solubility of group 2 metal sulfates follow in comparison to metal hydroxides?
hydroxides increase in solubilty
sulfates decrease in solubility
Why are the metal sulfates more soluble than the metal hydroxides in group 2?
because the sulfate ion is larger, and larger cations form stronger ionic compounds
How can barium sulfate be used?
in medicine, can be used as a contrast medium in certain types of X-ray due to its insoluble nature
can be used to allocate blockages in the digestive system
How can barium be used to test for sulfate ions in solution?
The insolubility of BaSO4 means that barium can also be used to test for sulfate ions in solution.
When barium chloride is added to a solution containing sulfate ions, the chloride ions will be displaced by the sulfate ions.
produces solid insoluble barium sulfate, which falls to the bottom of the reaction as a white precipitate.
Why does barium react slowly with sulfuric acid?
Barium reacts slowly with sulfuric acid because solid barium sulfate forms on the surface of the barium metal, slowing down the reaction
What states are fluorine, chlorine, bromine and iodine at room temperature?
gas
gas
liquid
solid
What color is fluorine, chlorine, bromine and iodine at room temperature?
pale yellow,
pale green,
dark orange liquid OR orange vapor
grey solid, purple vapor
What is the trend in electronegativity down group 7?
Electronegativity decreases down the group.
Why does electronegativity decrease down group 7?
because the atomic radii of the elements increase down the group, so the attraction between the nucleus and outer electrons decreases.
What happens to the melting point and the boiling point of the halogens down the group?
The melting and boiling point of the halogens increases down the group.
Explain why the MP/BP increases down group 7
molecules get larger down the group
more electrons therefor
and so increased Van der Waals
increased Van der Waals forces mean that more energy is needed to break the attraction between molecules, and so melting/ boiling point increases.
What charge ions do halogens form when they react with a metal?
1-
Why do halogens form a 1- ion when reacting with a metal?
They form these negative ions by oxidising metals to form positive metal ions (making them oxidising agents).
What happens when a metal is oxidised by a halogen to make a postive and negative ion?
They can come together to form an ionic compounds.
Then, these ionic substances can then undergo displacement reactions with other halogens. A displacement reaction is one in which a more strongly oxidising halogen replaces a weaker one in an ionic compound.
What determines which halogen will displace which in an ionic compound?
the oxidising strength of the halogen
Which compounds have the higher oxidation strength from chlorine, bromine and iodine?
- chlorine
- bromine
- iodine
What visible change would you be able to see if you added bromine to sodium chloride?
No reaction, solution remains orange.
What visible change would you be able to see if you added iodine to sodium chloride?
No reaction, solution remains brown.
What visible change would you be able to see if you added chlorine to sodium bromide?
Orange solution formed
What would the chemical reaction be if you added chlorine to sodium bromide?
Cl2 (aq) + 2Br- (aq) → 2Cl- (aq) + Br2 (aq)
What visible change would you see by adding iodine to sodium bromide?
No Reaction, solution remains brown.
What visible change would you see by adding chlorine to sodium iodide?
Brown solution formed
What visible change would you see by adding bromine to sodium iodide?
Brown solution formed
What is the chemical reaction for adding chlorine to sodium iodide?
Cl2 (aq) + 2I- (aq) → 2Cl- (aq) + I2 (aq)
What is the chemical reaction for adding bromine to sodium iodide?
Br2 (aq) + 2I- (aq) → 2Br- (aq) + I2 (aq)
Why can halides be identified in solution?
Because they form different coloured precipitates when they undergo certain reactions
How can you identify a halide ion?
To identify halide ions, an acidified silver nitrate solution (AgNO3) is added to the solution containing halide ions. Nitric acid is first added to react with any carbonates, hydroxides, or sulphites in the silver nitrate solution so that they will not form a precipitate that would interfere with the colour of the precipitates.
What is the visible change when you add silver nitrate to identify a fluoride ion and why?
No ppt. Silver fluoridei is soluble in water.
What is the chemical reaction for adding silver nitrate to identify a fluoride ion?
Ag+ (aq) + F- (aq) → AgF (aq)
What is the visible change when you add silver nitrate to identify a chloride ion?
A white ppt is formed
What is the visible change when you add silver nitrate to identify a bromide ion?
A cream ppt is formed
What is the visible change when you add silver nitrate to identify an iodide ion?
A pale yellow ppt is formed
What is the chemical reaction for adding silver nitrate to identify a chloride ion?
Ag+ (aq) + Cl- (aq) → AgCl (s)
What is the chemical reaction for adding silver nitrate to identify a bromide ion?
Ag+ (aq) + Br- (aq) → AgBr(s)
What is the chemical reaction for adding silver nitrate to identify a iodide ion?
Ag+ (aq) + I- (aq) → AgI (s)
What can be added to differentiate between the different silver halides?
Ammonia
Why is ammonia added to the different silver halides?
It can be difficult to differentiate between the different colours sometimes
What can be used to clearly identify chloride ions and why?
Dilute ammonia can be used to clearly identify Cl- ions since the precipitate dissolves.
What can be used to clearly identify I- ions and why?
Concentrated ammonia can be used to clearly identify I- ions as the precipitate is the only one that does not dissolve.
What is the reaction if you add dilute ammonia to AgF?
no reaction
What is the precipitate formed if you add dilute ammonia to AgF?
no ppt
What is the visible reaction when you add dilute ammonia to AgCl?
Silver chloride is dissolved by dilute ammonia
What happens to the precipitate formed when you add dilute ammonia to AgCl?
Silver chloride ppt dissolves into solution
What is the visible reaction when you add dilute ammonia to AgBr and why?
No reaction
Silver bromide is insoluble by dilute ammonia
What happens to the precipitate formed when you add dilute ammonia to AgBr?
cream ppt formed
What is the visible reaction when you add dilute ammonia to AgI and why?
No reaction
Silver iodide is insoluble in dilute ammonia
What happens to the precipitate formed when you add dilute ammonia to AgI?
yellow ppt formed
What is the visible reaction when you add concentrated ammonia to AgF?
no reaction
What is the visible reaction when you add concentrated ammonia to AgCl?
no reaction
What is the visible reaction when you add concentrated ammonia to AgBr?
silver bromide is dissolved by concentrated ammonia
What is the visible reaction when you add concentrated ammonia to AgI and why?
No reaction.
Silver iodide is insoluble in concentrated ammonia.
What happens to the precipitate formed when you add concentrated ammonia to AgF?
no ppt
What happens to the precipitate formed when you add concentrated ammonia to AgCl?
silver chloride ppt dissolves into solution
What happens to the precipitate formed when you add concentrated ammonia to AgBr?
silver bromide ppt dissolves into solution
What happens to the precipitate formed when you add concentrated ammonia to AgI?
yellow ppt formed
define an oxidizing agent
a species that accepts electrons
state and explain the trend in electronegativity for the elements down group 7
- electronegativity decreases down the group
- because atomic radii increases (shielding increases/ number of shells increase)
- so there is a weaker attraction between the nucleus and outer electrons
What is a reducing agent?
a reducing agent is a substance that reduces another substance that reduces another substance, while itself is oxidised
What is the reducing power of a substance?
its ability to reduce other substances
What is the trend in reducing power as you go down group 7?
increases down group 7
Why does reducing power of halides as you go down group 7?
As the ions get bigger, it is easier for outer electrons to be lost and taken by other substances, since the attraction between the nucleus and outer electrons is smaller.
What type of reaction occurs when you react fluoride and chloride containing halide salts with concentrated sulphuric acid?
acid base reaction
Why does an acid base reaction occur instead of a redox reaction when you react fluoride and chloride containing halide salts with concentrated sulphuric acid?
This happens because fluoride and chloride ions do not have a lot of reducing power, so cannot reduce sulfuric acid.
What are the chemical reactions for fluoride and chloride containing halide salts reacting with concentrated sulphuric acid?
NaF (s) + H2SO4 (l) → NaHSO4 (s) + HF (g)
NaCl (s) + H2SO4 (l) → NaHSO4 (s) + HCl (g)
What can be observed when you react fluoride and chloride containing salts with concentrated sulphuric acid?
white steamy fumes
What type of reaction do bromine containing halide salts undergo?
acid base reaction OR redox reaction
because of the strong reducing power of the bromide ions
Write two equations (acid-base and redox) to show how sodium bromide initially reacts with concentrated sulphuric acid
NaBr (s) + H2SO4 (l) → NaHSO4 (s) + HBr (g)
2HBr (aq) + H2SO4 (l) → Br2 (g) + SO2 (g) + 2H2O (l)
What observations would you see when sodium bromide initially reacts with concentrated sulphuric acid (acid base and redox)
- white steamy fumes of HBr released
- orange fumes from Br2 and colourless acidic gas, SO2 are evolved
Why can iodide ions react more readily than the other halide ions with sulphuric acid?
because iodide ions have a stronger reducing power than fluoride, chlorine and bromide ions
Write 4 equations to show the extent of how iodide ions can reduce H2SO4
1) NaI (s) + H2SO4 (l) → NaHSO4 (s) + HI (g)
2) 2HI (g) + H2SO4 (l) → I2 (s) + SO2 (g) + 2H2O (l)
3) 6HI (g) + H2SO4 (l) → 3I2 (s) + S (s) + 4H2O (l)
4) 8HI (g) + H2SO4 (l) → 4I2 (s) + H2S (g) + 4H2O (l)
What observations could be observed and why when you react iodide ions with sulphuric acid
- HI is released in the form of white misty fumes.
- When iodine is produced, purple fumes are released and a black solid is formed.
- When sulphur is produced, a yellow solid is formed.
- When H2S is formed fumes with a strong eggy smell are evolved.
How does chlorine react with water with the presence of bright sunlight?
In the presence of bright sunlight, chlorine reacts with water to produce hydrochloric acid and oxygen.
What is the chemical reaction for chlorine reacting with water in bright sunlight?
2Cl2 (g) + 2H2O (l) → 4HCl (aq) + O2 (g)
How does chlorine react with water without the presence of bright sunlight?
In the absence of sunlight, disproportionation takes place. This is because chlorine is both oxidised and reduced, resulting in chloride ions (Cl-) and chlorate (I) ions (ClO-) being formed.
What is the chemical reaction for chlorine and water without the presence of sunlight?
Cl2 (g) + H2O (l) ⇌ HClO (aq) + HCl (aq)
How does chlorine react with sodium hydroxide?
In a reaction between chlorine and cold sodium hydroxide, water, sodium chloride and sodium chlorate (NaClO) are formed.
What is the chemical equation for chlorine reacting with sodium hydroxide?
Cl2 (aq) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (l)
Evaluate how chlorine can be used
- commonly used as a water treatment because it is effective in killing bacteria.
- although chlorine can have some toxic effects, it is only used in small amounts
so the benefits far outweigh the drawbacks.
How can the reaction between chlorine and sodium hydroxide be used in industry?
It makes sodium chlorate which can be used as bleach
RP 4- How can group 2 metals be identified? (3)
- reacting them with ammonium solution
- dilute sodium hydroxide
- dilute sulphuric acid
RP4- How does ammonium solution test for group 2 cations?
magnesium will be the only one to form a white precipitate
RP4- How can dilute sodium hydroxide be used to test for group 2 metal cations?
- Mix an equal amount of the test solution containing the group 2 metal cation and dilute sodium hydroxide.
- Then continue adding sodium hydroxide dropwise until it is in excess.
Group 2 metal cations usually form a colourless solution. In excess NaOH, some of them will form precipitates
RP4- What do Mg, Ca, Ba and Sr do when they react with dilute hydroxide and in excess?
Equal volume of NaOH
Mg- off white ppt
Ca- off white ppt
Ba- colourless solution
Sr- off white ppt
Excess NaOH
Mg- white ppt
Ca- off white ppt
Ba- colourless solution
Sr- off white ppt
RP 4- How can dilute sulphuric acid be used to test for group 2 cations?
- In a test tube, mix an equal amount of the test solution containing the group 2 metal cation and dilute sulfuric acid.
- Then continue adding sulfuric acid by drops until it is in excess.
RP 4- What would the results be after reacting group 2 cations with sulphuric acid, and in excess
Equal volume of H2SO4
Mg- white ppt
Ca- off white ppt
Ba- off white ppt
Sr- white ppt
Excess H2SO4
Mg- white ppt
Ca- off white ppt
Ba- colourless solution
Sr- white ppt
RP 4- How can ammonium ions be identified?
reacting them with sodium hydroxide solution
RP 4- Describe a test for ammonium ions with sodium hydroxide solution
- In a test tube, mix an equal amount of the solution containing ammonium ions and sodium hydroxide solution.
- Warm the mixture gently. If ammonium ions are present, fumes of ammonia gas should evolve.
- Place damp red litmus paper at the mouth of the test tube. If the litmus paper changes colour to blue, the gas is ammonia and ammonium ions must be present.
RP 4- How can you test for hydroxide ions?
Damp red litmus paper will turn blue when placed in an aqueous solution containing hydroxide ions.
RP 4- What chemical can you use to test for carbonate ions?
Carbonate ions can be identified through a reaction with hydrochloric acid.
RP4- Describe how you could test for carbonate ions
- In a test tube, mix an equal amount of the test solution containing carbonate ions and dilute hydrochloric acid.
- Bubble the gas produced through limewater. If the lime water goes cloudy, carbonate ions are present.
RP 4- What can you use to identify sulphate ions?
Sulphate ions can be identified through a reaction with barium chloride
RP 4- Describe how you would test for sulphate ions
- In a test tube, mix an equal amount of the substance containing sulfate ions, dilute hydrochloric acid and barium chloride.
- If a white precipitate is formed, sulfate ions are present
RP4- Describe how to test for halide ions (aqueous)
Halide ions in an aqueous solution can be identified through a reaction with silver nitrate. For different halides, different coloured precipitates are formed.
RP4- What chemical can be used to test for solid halide ions?
Halide ions in solids can be identified through a reaction with concentrated sulfuric acid.
RP4- Describe how you would test for solid halide ions using concentrated sulphuric acid
- Using a spatula, place a small amount of the solid containing halide ions into a test tube and then add a few drops of concentrated sulfuric acid.
- Record the observation.
- Fumes from the above reaction should always turn damp blue litmus paper red if halide ions are present
RP4- What would the results be if you tested the halide ions with concentrated sulphuric acid?
Chloride- white, steamy fumes
Bromide- orange fumes
Iodide- Purple fumes and black ppt
