C10. The Halogens Flashcards
What are the trends going down group 7?
Boiling point increases - More van der waals forces, increasing size and relative mass of atoms; Physical states go from gas to solid; Electronegativity decreases - Atomic radius increases, shielding increases; Less oxidising; Less reactive - Atomic radius increases
What are the physical appearances of F2, Cl2, Br2, I2?
F2, pale yellow gas; Cl2, pale green gas; Br2, brown-orange liquid; I2, grey solid
What is the prerequisite for displacement reactions to occur with halogens?
Halogen will displace halide ion if halide ion is less reactive (lower in the periodic table)
What is the half equation and observations of addition of chlorine water to potassium bromide?
Orange solution, Br2 formed;
Cl2 + 2Br- => 2Cl- + Br2
What is the half equation and observations of addition of chlorine water to potassium iodide solution?
Brown solution, I2 formed; Cl2 + 2I- => 2Cl- + I2
What is a disproportionation reaction?
A reaction where a compound is simultaneously reduced and oxidised
How is bleached created?
Disproportionation reaction; Mixing chlorine and sodium hydroxide will form sodium chlorate(I) solution (bleach)
2NaOH(aq) + Cl2(g) => NaClO(aq) + NaCl(aq) + H2O(l)
What are the uses of Sodium Chlorate(I)?
Treating water; Bleaching fabric, papers; Cleaning agent
How does chlorine sterilise water and what is the equation?
Water + Chlorine = Chlorate(I) ions which kill bacteria;
H2O(l) + Cl2(g) => 2H+(aq) + Cl-(aq) + ClO-(aq); Disproportionation reaction;
Why does chlorine have to be regularly replaced in swimming pools (use an equation to prove)?
Sunlight decomposes chlorinated water, no chlorate(I) ions produced;2H2O(l) + Cl2(g) => 4H+(aq) + 2Cl-(aq) + O2(g)
What are the advantages of chlorinating water?
Destroys microorganisms; Long lasting, reduces bacteria build up; Reduce growth of algae which discolour water and give it bad tase and smell
What are the disadvantages of chlorinating water?
Chlorine gas is toxic and irritates respiratory system; Liquid chlorine causes severe chemical burns; Chlorine can react with organic compounds formine chloroalkanes , linked to causing cancer
Are halide ions oxidising or reducing and why?
Reducing; Halogens gain an electron becoming -1 halide ions; Extra electron is removed
What are the trends in ions going down group 7?
Ionic radius increases; Distance between nucleus and outer electron increases; More shielding; Attractive forces get weaker; Outer electron more readily lost; I- stronger reducing agent than F-
How do chlorine level chlorides react with concentrated sulfuric acid?
Not redox reaction; NaCl, NaBr, NaI react same first stage;
H2SO4 + NaCl => NaHSO4 + HCl; White misty fumes produced
How do bromide level ions react with concentrated sulfuric acid?
Redox reaction; I-, Br- react same second stage;
2Br- => Br2 + 2e- (Br is oxidised)
H2SO4 + 2H+ + 2e- => SO2 + 2H2O (S is reduced)
H2SO4 + 2H+ +2Br- => SO2 + Br2 + 2H2O (overall ionic); In addition to NaBr; Orange vapour of Br2 produced
How do Iodide level ions react with concentrated sulfuric acid?
In addition to NaI, I2;
6I- => 3I2 + 6e- (I- ion oxidised)
H2SO4 + 6H+ + 6e- => S + 4H2O (S being reduced)
H2SO4 + 6H+ 6I- => 3I2 + S + 4H2O (overall ionic); Yellow solid produced (S);
8I- => 4I2 + 8e- (I- oxidised)
H2SO4 + 8H+ + 8e- => H2S + 4H2O (S being reduced)
H2SO4 + 8H+ + 8i- => 4I2 + H2S + 4H2O (overall ionic); Rotten egg smell (H2S)
What is the test for identifying halide ions?
Add dilute nitric acid (HNO3 reacts with any anions aside aside from halides); Add silver nitrate solution (AgNO3); Cl ions white precipitate, Br ions cream precipitate, I ions yellow precipitate; Add ammonia solution (NH3); Cl- dissolves in dilute NH3; Br dissolves in concentrated NH3; I- insoluble in concentrated NH3
What is the test for group 2 anions?
Dip nichrome wire in concentrated HCl; Dip into sample; Place loop into blue bunsen flame; Ca2+ dark red, Sr2+ red, Ba2+ green
What is the test for ammonia compounds?
Add NaOH, gently heat; NH3 gas produced; Test w/ damp red litmus paper; NH3 will dissolve in water and turn litmus blue;
NH4+(aq) + OH-(aq) => NH3(g) + H2O(l)
What is the test for hydroxides?
Hydroxides are alkaline; Turn red litmus paper blue; Not definitive; Red litmus turns blue in any alkali, further tests are needed
What is the test for carbonates?
HCl reacts with carbonates to form CO2(g); Bubble through limewater, turns cloudy;
CO3(2-) + 2H+ => CO2 + H2O
What is the test for sulfates?
Add HCl to remove carbonates; Add Barium Chloride; White precipitation (BaSO4);
Ba(2+)(aq) + SO4(-2)(aq) => BaSO4(s)
What is the order to tests unknown ions in?
Test for carbonates, CO2(g) produced?; Test for sulfates, BaSO4 precipitate?; Test for halides. white, cream, yellow precipitates?
