G7 (KEY MEMORY) Flashcards by Saleh Taha

What are the 4 steps in testing for halide ions

1) Add HNO3
2) Add AgNO3
3) Add dilute NH3
4) Add concentrated NH3

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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)

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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)

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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)

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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)

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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)

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What is the chemical formula for bleach

Sodium Chlorate(I)

NaClO

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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

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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)

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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)

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What is observed when a solution of KCl is added to a solution of chlorine

Very pale green solution, no reaction

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What is observed when a solution of KCl is added to a solution of bromine

Yellow-orange solution, no reaction

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What is observed when a solution of KCl is added to a solution of iodine

Brown solution, no reaction

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What colour is a test tube with chlorine present in solution

Very pale green solution (often colourless)

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What colour is a test tube with bromine present in solution

Yellow - orange solution

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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

Write equations and state the observations for the reaction of NaF and NaCl with H2SO4 State what type of reaction occurs

NaF(s) + H2SO4(l) ---> NaHSO4(s) + HF(g) White steamy fumes of HF are evolved. NaCl(s) + H2SO4(l) ----> NaHSO4(s) + HCl(g) Observations: White steamy fumes of HCl are evolved. F- and Cl- ions are not strong enough reducing agents to reduce the S in H2SO4. No redox reactions occur. Only acid-base reactions occur.

What is the role of H2SO4 when it reacts with NaF or NaCl

H2SO4 plays the role of an acid (proton donor).

Write equations and state the observations for the reaction of NaBr with H2SO4 State what type of reactions occur

Acid- base step: NaBr(s) + H2SO4(l) ---> NaHSO4(s) + HBr(g) White steamy fumes of HBr are evolved. Redox step: 2HBr + H2SO4 ---> Br2(g) + SO2(g) + 2H2O(l) Red fumes of Bromine are also evolved and a colourless, acidic gas SO2 H2SO4 plays the role of acid in the first step producing HBr and then acts as an oxidising agent in the second redox step.

Write the half equations for the reaction of NaBr with H2SO4

Ox ½ equation 2Br- ---> Br2 + 2e- Re ½ equation H2SO4 + 2 H+ + 2 e- ---> SO2 + 2H2O LEARN HALF EQUATIONS THEN CAN PUT TOGETHER FULL EQUATIONS IN EXAM

Write equations and state the observations for the reaction of NaI with H2SO4 State what type of reactions occur

NaI(s) + H2SO4(l) ---> NaHSO4(s) + HI(g) White steamy fumes of HI are evolved. 2HI + H2SO4 ---> I2(s) + SO2(g) + 2H2O(l) Black solid and purple fumes of Iodine are also evolved A colourless, acidic gas SO2 6HI + H2SO4 ---> 3I2 + S (s) + 4H2O (l) A yellow solid of Sulphur 8HI + H2SO4 ---> 4I2(s) + H2S(g) + 4H2O(l) H2S (Hydrogen Sulphide), a gas with a bad egg smell H2SO4 plays the role of acid in the first step producing HI and then acts as an oxidising agent in the three redox steps

Write the half equations for the reactions of NaI with H2SO4

(1) Ox ½ equation 2I - ---> I2 + 2e- Re ½ equation H2SO4 + 2 H+ + 2 e- ----> SO2 + 2H2O (2) Ox ½ equation 2I - ---> I2 + 2e- Re ½ equation H2SO4 + 6 H+ + 6 e- ----> S + 4H2O (3) Ox ½ equation 2I - ---> I2 + 2e- Re ½ equation H2SO4 + 8 H+ + 8 e- ----> H2S + 4H2O LEARN HALF EQUATIONS THEN CAN PUT TOGETHER FULL EQUATIONS IN EXAM

Write the half equation for the formation of Br2 from Br- State whether this is oxidation or reduction

Ox ½ equation 2Br- ---> Br2 + 2e-

Write the half equation for the formation of I2 from I- State whether this is oxidation or reduction

Ox ½ equation 2I - ---> I2 + 2e-

Write the half equation for the formation of SO2 from H2SO4 State whether this is oxidation or reduction

H2SO4 + 2 H+ + 2 e- ---> SO2 + 2H2O

Write the half equation for the formation of S from H2SO4 State whether this is oxidation or reduction

H2SO4 + 6 H+ + 6 e- ----> S + 4H2O

Write the half equation for the formation of H2S from H2SO4 State whether this is oxidation or reduction

H2SO4 + 8 H+ + 8 e- ----> H2S + 4H2O

What does the MS often put in the H2SO4 with halide redox equations

Instead of HI etc, they put H+ + I-

What is the equation to show how AgCl dissolves in dilute NH3

AgCl(s) + 2NH3(aq) → Ag(NH3)2+(aq) + Cl−(aq)

What is the equation to show how AgBr dissolves in excess dilute NH3

AgBr(s) + 2NH3(aq) → [Ag(NH3)2]+(aq) + Br−(aq)