Chapter 8 Groups Flashcards
What are the chemical properties of all group 2 elements, in terms of redox?
Easily oxidised (lose two electrons)
Good reducing agents
e.g Mg –> Mg2+ + 2e-
What are the products when Mg reacts with Oxygen?
MgO
What are the products when Mg reacts with Water?
Magnesium Hydroxide and Hydrogen gas
What are the products when Mg reacts with HCL?
Magnesium Chloride and Hydrogen Gas
What are the product(s) when MgO reacts with water?
Magnesium Hydroxide
What is the trend in solubility of group 2 hydroxides?
Down the group, solubility increase usually aqueous from around Calcium Hydroxide
What is the trend in pH of group 2 hydroxide solutions?
pH increases, greater alkalinity
More soluble down the group, greater percentage of OH- ions released, increase pH
What is the trend in reactivity down group 2 and why?
At each new period, a new shell is added, further from the nucleus, increasing atomic radius
Also more electron shielding with more shells
Therefore, there is a decrease in nuclear attraction upon the outer shell, decrease first ionisation energy
Therefore reactivity increases
What are uses of group 2 products in life?
Agriculture- Calcium Hydroxide used to treat acidic soil
Medicine- Magnesium Carbonate/ Hydroxide used to treat acid reflux, neutralise excess stomach HCl
What is the trend in boiling down the halogens and why?
Down the group, the number of electrons of each molecule increases
Increases the strength of instantaneous and induced dipoles, increasing the strength of the london forces
More energy needed to overcome the stronger intermolecular forces, higher boiling point
What are the colours of the halogens naturally?
Fluorine= Pale Yellow Gas
Chlorine= Pale Green Gas
Bromine= Orange/Brown liquid
Iodine= Purple liquid/ vapour, grey crystalline solid
What are the chemical properties of the halogens in terms of redox?
Very easily reduced
Very good oxidising agents
What are halogen-displacement reactions?
A more reactive halogen will displace a less reactive halogen in a compound
Why and what solvent is used in halogen displacement reactions?
Cyclohexane, non polar easily dissolves non polar halogen
Top layer shows more distinct halogen colour to avoid confusion
What are the colours of the halogens in cyclohexane?
Chlorine=Pale Green
Bromine=Orange
Iodine=Violet
What is the trend in reactivity down the halogens and why?
At each period, a new shell is added which is further away from the nucleus, increasing atomic radius
Increased electron shielding with new shells
Decreases the nuclear attraction upon the outer shell, making it harder to gain an electrons, so decreases reactivity
What are disproportion reactions?
Redox reactions where the same element is oxidised and reduced in the same reaction
Give the equation for the reaction of Chlorine with water
Chlorine + Water —> Hydrochloric Acid + Chloric(I) acid
Cl2 + H20 —> HCl + HClO
Give the equation of the reaction of Chlorine with Sodium Hydroxide.
What conditions are necessary?
Chlorine + Sodium Hydroxide—> Sodium Chloride + Sodium Chlorate(I) + water
Cl2 + NaOH—> NaCl + NaClO + H2O
Needs to be cold and dilute NaOH
Which reaction pathway produces bleach more commonly? How does bleach work?
Reaction of dilute, cold NaOH with chlorine
Chlorate ions kill bacteria
How can bleach be detected with indicator?
Turns red then bleached white
What are the disadvantages of using chlorine in water purification?
Can kill bacteria which could otherwise cause disease
However:
Chlorine gas is toxic and can be a respiratory irritant
Chlorine can react with organic compounds from decaying vegetation in light to form haloalkanes, which are suspected carcinogens
What is qualitative analysis?
Relying on simple observations such as bubbles, colours or precipitates to identify compound
What is the carbonate test? Give the ionic equation
Add dilute, aqueous HNO3. If it bubbles, carbonates present, check by pumping into lime water Ca(OH)2
CO3 2- + 2 H+ —-> CO2+ H2O
What is the sulphate test? Give the ionic equation
Add aqueous Barium Nitrate. A white precipitate forms
Ba2+ + SO4 2- —–> BaSO4
What is the halide test?
Add aqueous Silver Nitrate. If a precipitate forms, halide present. Add excess NH3, dilute then aqueous
Cl-= White, soluble in dilute NH3
Br-= Cream, soluble in concentrated NH3
I-=Yellow, insoluble in NH3
What is the correct sequence of qualitative tests and why?
Carbonate, then Sulphate, then Halide
False positive from carbonates for sulphate and Halide
False positive from sulphate for halides
Therefore, sometimes add HNO3 before each test
What is the test for ammonium ions?
Add NaOH, if ammonia gas produced, distinct smell, but soluble in water so heat gentle
Damp red pH paper, moist, blue= positive test
Why is the reaction of chlorine and water not used often to produce bleach?
The reaction is limited by the low solubility of chlorine in water
So greater yield with NaOH
What are the products of when fluorine reacts with water?
Varies
Normally HF and oxygen
What is the observation when AgNO3 reacts with Na2SO4
White precipitate forms
Links to test, if sulphate ions present, precipitate forms with halide test, so need to be removed with Barium ions
What is the process of carrying out multiple tests on the same sample?
Add HNO3, if fizzing, keep adding until fizzing stops to remove all the CO3 2- ions
Add Ba(NO3)2. If a precipitate forms, add excess, filter out.
Halide test, remove with ammonia.
No halide ions so no HCl, no BaCl2
Why should you work in a well ventilated area for halogen displacements?
Bromine toxic
Cyclohexane solvent toxic
