G7 (KEY MEMORY)
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What are the 4 steps in testing for halide ions
1) Add HNO3 2) Add AgNO3 3) Add dilute NH3 4) Add concentrated NH3
Why do we add HNO3 (nitric acid) in the first step of identifying halide ions (why is silver nitrate acidified) Write an equation for this reaction
Removes Co32- ions (essential as Ag2CO3 is a white ppt) 2 HNO3 + Na2CO3 —> 2 NaNO3 + H2O + CO2 (Na is from compound like NaBr)
Which element is clearly identified after adding DILUTE NH3 in the halide ion test. Write the equation for this reaction
Cl- (In Cl- white ppt dissolves, Br- and I- have no visible change) AgCl(s) + 2NH3(aq) —> [Ag(NH3)2]+(aq) + Cl- (aq)
Which element is clearly identified after adding CONCENTRATED NH3 in the halide ion test. Write the equation for this reaction
Br- (In Br- cream ppt dissolves, I- has no visible change) AgBr(s) + 2NH3(aq) —> [Ag(NH3)2]+ (aq) + Br - (aq)
What is the equation for the reaction of chlorine and water without UV light, what type of reaction is this
Cl2 + H2O –>HCl + HClO (reversible) Ionic: Cl2 + H2O –> 2H+ + Cl- + ClO- (Reversible) Disproportionation reaction (Cl2 both oxidised and reduced)
What is the equation for the reaction of Cl and water with UV (sunlight)
2Cl2 + 2H2O —> 4HCl + O2 Ionic: 2Cl2 + 2H2O —> 4H+ + 4Cl- + O2 (Green colour of Cl2 slowly fades as it reacts)
What is the chemical formula for bleach
Sodium Chlorate(I) NaClO
What is the equation for the manufacture of bleach What is the colour change for this reaction
Cl2 + 2NaOH –> NaCl + NaClO + H2O Ionic: Cl2 + 2OH- —> Cl- + ClO- + H2O Pale green to colourless
State the colours of precipitate formed when AgNO3 is added to Cl-,Br-, and I- Write the ionic equation for each
Chloride (Cl-) ions: Produce a white precipitate of silver chloride Ag+(aq) + Cl-(aq) –> AgCl(s) Bromide (Br-) ions: Produce a cream precipitate of silver bromide Ag+(aq) + Br-(aq) –> AgBr(s) Iodide (I-) ions: Produce a yellow precipitate of silver iodide Ag+(aq) + I-(aq) –> AgI(s)
What is the trend in reactivity of G7 HALIDES
Reactivity increases up the group For atoms reactivity increases down the group This is because halogen atoms are oxidising agents, and halide ions are reducing agents (e.g. they can reduce H2SO4)
What is observed when a solution of KCl is added to a solution of chlorine
Very pale green solution, no reaction
What is observed when a solution of KCl is added to a solution of bromine
Yellow-orange solution, no reaction
What is observed when a solution of KCl is added to a solution of iodine
Brown solution, no reaction
What colour is a test tube with chlorine present in solution
Very pale green solution (often colourless)
What colour is a test tube with bromine present in solution
Yellow - orange solution
What colour is a test tube with iodine present in solution
Brown solution (sometimes black solid present)
What is observed when a solution of KBr is added to a solution of chlorine Write the ionic equation for this reaction
Yellow-orange solution, Cl has displaced Br Cl2(aq) + 2Br –(aq) –> 2Cl –(aq) + Br2(aq) (NOT BROWN COS THATS I2)
What is observed when a solution of KBr is added to a solution of bromine
Yellow-orange solution, no reaction
What is observed when a solution of KBr is added to a solution of iodine
Brown solution, no reaction
What is observed when a solution of KI is added to a solution of chlorine Write the ionic equation for this reaction
Brown solution, Cl has displaced I Cl2(aq) + 2I–(aq) –> 2Cl –(aq) + I2(aq)
What is observed when a solution of KI is added to a solution of bromine Write the ionic equation for this reaction
Brown Solution, Br has displaced I Br2(aq) + 2I–(aq) —> 2Br–(aq) + I2(aq)
What is observed when a solution of KI is added to a solution of iodine
Brown Solution, no reaction
What does the colour of a test tube after a halogen displacement reaction tell us
The colour of the solution in the test tube shows which free halogen is present in solution. (NOT HALIDE ION) Chlorine =very pale green solution (often colourless), Bromine = yellow-orange solution Iodine = brown solution (sometimes black solid present)
Sketch the sable showing the products of the reaction between concentrated H2SO4 and Cl-, Br- and I-
NaF is the same as Cl
