Elements From The Sea

Question 1

Give the reaction of hydrogen bromide with conc. sulfuric acid

Answer 1

2HBr + H2SO4 -> SO2 + Br2 + 2H2O

Question 2

Give the reaction for hydrogen iodide with conc. sulfuric acid

Answer 2

8HI + H2SO4 -> H2S + 4I2 + 4H2O

Question 3

What alternative oxidising agent for sulfuric acid can be used to create pure HBr and HI?

Answer 3

Phosphoric acid

Question 4

The thermal stability of the hydrogen halides _______ down the group

Answer 4

Decreases

Question 5

When dynamic equilibrium has been reached, what happens to the concentrations and reactions rates?

Answer 5

The concentrations remain CONSTANT
The backward and forward reaction RATES EQUAL

Question 6

What effects do the following factors have on the equilibrium constant? :
Pressure
Temperature
Concentration

Answer 6

Pressure -> no effect
Temperature -> will effect
Concentration -> no effect

Question 7

What do half equations involve?

Answer 7

Transfer of electrons

Question 8

Give the equation for the production of oxygen during electrolysis

Answer 8

4OH- -> O2 + 2H2O + 4e-

Question 9

What are the physical states and colours of the halogens (Cl, Br, I) at room temperature?

Answer 9

Cl2 -> Pale green gas
Br2 -> Orange liquid
I2 -> Grey solid

Question 10

What is the colour of iodine in aqueous solution, and in an organic solvent?

Answer 10

Aqueous -> Brown
Organic -> Purple

Question 11

What three positive ions are always soluble?

Answer 11

Potassium, Sodium, Ammonium

Question 12

What negative ion is always soluble?

Answer 12

Nitrate

Question 13

What ions will form a precipitate with OH- ions? Give their colours

Answer 13

Cu2+ -> Blue ppt of Cu(OH)2
Fe2+ -> Green ppt of Fe(OH)2
Fe3+ -> Orange-brown ppt of Fe(OH)3+

Question 14

What are the two major concerns about the danger of chlorine?

Answer 14

•Toxic to life
•Volatile; readily becomes gaseous

Question 15

Give the equation for atom economy

Answer 15

% atom economy = (mr of desired product/mr of all products) × 100

Question 16

What are the conditions for an ion to be reduced during aqueous electrolysis? Which electrode does this occur at?

Answer 16

Not part of group 1, 2 or Aluminium, occurs at the cathode

Question 17

What are the conditions for an ion to be oxidised during electrolysis? What electrode does this occur at?

Answer 17

Must be a halide ion, occurs at the anode

Question 18

Describe how you could investigate the relative reactivates of 1-iodo/chloro/bromobutane. Explain the results, giving relevant equations where appropriate

Answer 18

• Add equal volumes of each haloalkane to seperate test tubes
• Use same volume of ethanol as a co-solvent/universal solvent
• Add same volume of AgNO3 solution to 3 test tubes
• Place all test tubes in a water bath and give time for the temperatures to equilibriate
• Add the AgNO3 to the haloalkanes and time how long it takes for a precipitate to form/red cross method
• RX + H2O > ROH + H+ + X-
• Ag+(aq) + X-(aq) > AgX(s)
• Iodo will form a precipitate/obscure the cross fastest, and chlorine the slowest
•Reactivity is dependent on the bond enthalpy/strength; C-Cl is the strongest and C-I is the weakest