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Chem 3: Elements of the Sea > ES5: Chlorine + Iodine Sodium Thiosulfate Titration > Flashcards

ES5: Chlorine + Iodine Sodium Thiosulfate Titration Flashcards

1
Q

What are the risks of chlorine?

A
  • Toxic and corrosive so must be kept away from the skin and eyes
  • Dangerous to be inhaled at high concentrations
  • Must be kept away from flammable materials
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2
Q

Why must chlorine be kept away from flammable materials?

A

Because it is a powerful oxidising agent

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3
Q

Why is inhaling chlorine dangerous?

A
  • Reacts in the lungs to form HCl
  • This corrodes lung tissue
  • Drowns the person as liquid fills the lungs
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4
Q

What is chlorine stored in as it is transported?

A
  • Specially designed pressurised tank containers

- In cylinders

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5
Q

How does chlorine travel?

A

By road or by rail

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6
Q

What state is chlorine transported in?

A

Liquid

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7
Q

Why is chlorine transported as a liquid?

A

More chlorine can be stored in a fixed volume under pressure as a liquid than a gas

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8
Q

What do tanks used to transport chlorine have if the temperature/pressure gets too high?

A

Pressure release devices which vent the tank and release chlorine gas

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9
Q

What are the tanks used to transport chlorine made and lined with

A

Steel

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10
Q

What to do the inside of the tanks used to transport chlorine need to be?

A

Dry

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11
Q

Why do the inside of the tanks used to transport chlorine need to be dry?

A

Because chlorine reacts with water to produce HCl which is corrosive

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12
Q

What to the tanks used to transport chlorine have at the top?

A

Cylindrical protective housing through which all loading and unloading is done

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13
Q

What do the tanks used to transport chlorine have in them for safety during unloading?

A

A scrubber unit which ensures all air being displaced has chlorine removed

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14
Q

Name 2 uses of chlorine

A
  • Water treatment

- Bleach

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15
Q

How is chlorine used in water treatment?

A
  • To sterilise water for drinking/swimming
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16
Q

How is chlorine used in bleach?

A
  • To remove stains from clothing

- To kill bacteria on surfaces

17
Q

What are iodine-sodium thiosulfate titrations used for?

A

To find the concentration of an oxidising agent

18
Q

Describe a method for an iodine-sodium thiosulfate titration

A
  • Measure out a certain volume of the oxidising agent and pipette into a conical flask
  • Add excess potassium iodide + sulfuric acid
  • Put sodium thiosulfate in the burette
  • After the solution fades to pale yellow, add 2cm3 of starch solution in the flask as an indicator for iodine - turning blue when the iodine is detected
  • Add sodium thiosulfate one drop at a time until the blue colour disappears
  • Measure the amount of sodium thiosulfate needed to do this
  • Repeat
19
Q

What happens after potassium iodide is added to the oxidising agent? Give an equation with chlorate as the oxidising agent

A
  • Oxidising agent oxidises iodide ions to iodine

ClO- + 2I- + 2H+ =====> I2 + H2O + Cl-

20
Q

Give an equation for the reduction of iodine ions by sodium thiosulfate.

A

I2(aq) + 2S2O3^2- (aq) =====> 2I- (aq) + S4O62- (aq)

21
Q

What are the steps for calculating the concentration of an oxidising agent?

A
  • Convert all cm3 readings to dm3
  • Write the 2 ionic equations for the titration and calculate their stoichiometry
  • Calculate the moles of sodium thiosulfate
    (moles=conc x volume)
  • Calculate moles of iodine
    (moles of thiosulfate/2)
  • Calculate the moles of the oxidising agent
    (Use ratio of iodine produced:oxidising agent)
  • Calculate the conc. of the oxidising agent
    (conc=moles/volume)
22
Q

What’s the unit for concentration?

A

moldm-3

23
Q

Name 5 problems that could arise in a iodine-sodium thiosulfate titration

A
  • Contaminated apparatus could make inaccurate results
  • Burette could be read incorrectly
  • Random errors
  • Solutions could react with oxygen in the air
  • Adding starch too soon could make iodine “stick to the starch” and not react properly with the sodium thiosulfate
24
Q

What is the solution to the problem of contaminated apparatus making inaccurate results?

A
  • Ensure the burette is very clean

- Rinse with sodium thiosulfate (water could dilute the solution)

25
Q

What is the solution to the problem of the burette being read incorrectly?

A
  • Always read from the bottom of the meniscus

- Keep eyes level with the liquid

26
Q

What is the solution to the problem of random errors?

A

Repeat experiment until you obtain 3 results within 0.1cm3 of each other then take an average

27
Q

What is the solution to the problem of solutions reacting with oxygen air?

A

Solutions should be made up freshly

28
Q

What is the solution to the problem of adding starch too soon making iodine “stick to the starch” and not react with the sodium thiosulfate?

A

Only add the starch when the solution is pale yellow

Chem 3: Elements of the Sea (7 decks)

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