Chapter 8 Groups
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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