(a) In the Solvay process, explain briefly with equations the functions of the following substances:
(b) (i) Write a chemical equation for the fermentation of glucose.
(ii) Explain briefly why a tightly-corked glass bottle filled to the brim with fresh palm-wine shatters on standing for some time.
(c) Consider the following metals: Na, Fe, K and Cu.
(i) Arrange the metals in order of increasing reactivity.
(ii) Which of the metals will react with cold water?
(ii) Which of the metals could form coloured salts?
(d)(i) What is a redox reaction?
(ii) Identify which of the following reaction equations are redox.
(i) 2Na + Cl\(_2\) ? 2NaCl
(ii) AgCl + 2NH\(_3\) ? [Ag(NH\(_3\))\(_2\)]Cl
(iii) C\(_2\)H\(_2\) + H\(_2\) ? C\(_2\)H\(_4\)
(IV) HCl + KOH ? KCl + H\(_2\)O
(V) 2FeCl\(_3\) + 2KI ? 2FeCl\(_2\) + 2KCl + I\(_2\)
(iii) Give a reason for each of the answers in (d)(ii).
(iv) Write balanced equations of the half reactions for any two of the redox reactions in (d)(ii).
Solvay Process and Chemical Reactions
(a) Functions in the Solvay Process:
- Limestone (CaCO3):
- Function: Source of calcium oxide (CaO) for the regeneration of ammonia.
- Equation: CaCO3 (g) -> CaO (s) + CO2 (g) (Limestone decomposes to lime and carbon dioxide)
- Ammonia (NH3):
- Function:
- Reacts with calcium and chloride ions in brine to form ammonium chloride (NH4Cl).
- Makes the solution alkaline, favoring the precipitation of calcium carbonate.
- Equation: Not directly involved in a reaction, but participates in the overall process.
(b) Fermentation and Shattered Bottle:
(i) Glucose Fermentation:
C6H12O6 (aq) -> 2C2H5OH (aq) + 2CO2 (g) (Glucose ferments to ethanol and carbon dioxide)
(ii) Shattered Bottle:
Fresh palm wine undergoes fermentation by yeast. During fermentation, yeast consumes sugar and produces carbon dioxide gas. In a tightly sealed bottle, the CO2 gas gets trapped and builds up pressure. As pressure increases, the glass bottle can no longer withstand the force and shatters.
(c) Metal Reactivity:
(i) Increasing Reactivity: K > Na > Fe > Cu
(ii) Reacting with Cold Water: K, Na (These alkali metals react vigorously with water)
(iii) Colored Salts: Cu (Copper forms characteristic colored salts, like blue copper sulfate)
(d) Redox Reactions and Half Reactions:
(i) Redox Reaction:
A redox reaction is a type of chemical reaction where there is a transfer of electrons between the participating atoms or ions. Oxidation is the loss of electrons, and reduction is the gain of electrons.
(ii) Identifying Redox Reactions:
- Redox: (II), (V)
- Not Redox: (I), (III), (IV)
(iii) Explanation for Redox Reactions:
- (II) AgCl + 2NH3 -> [Ag(NH3)2]Cl:
- Silver (Ag) loses an electron to become Ag+ (oxidation).
- Nitrogen (N) in ammonia gains an electron to form the complex ion [Ag(NH3)2]+ (reduction).
- (V) 2FeCl3 + 2KI -> 2FeCl2 + 2KCl + I2:
- Iron (Fe) in FeCl3 loses an electron to become Fe2+ in FeCl2 (oxidation).
- Iodine (I) gains an electron to form I2 (reduction).
(iv) Balanced Half Reactions (Examples):
- Oxidation Half Reaction (from reaction II):
Ag -> Ag+ + e-
- Reduction Half Reaction (from reaction V):
I- -> I2 + e- (Note: I- needs to be balanced with Cl- from the reactant side)
Solvay Process and Chemical Reactions
(a) Functions in the Solvay Process:
- Limestone (CaCO3):
- Function: Source of calcium oxide (CaO) for the regeneration of ammonia.
- Equation: CaCO3 (g) -> CaO (s) + CO2 (g) (Limestone decomposes to lime and carbon dioxide)
- Ammonia (NH3):
- Function:
- Reacts with calcium and chloride ions in brine to form ammonium chloride (NH4Cl).
- Makes the solution alkaline, favoring the precipitation of calcium carbonate.
- Equation: Not directly involved in a reaction, but participates in the overall process.
(b) Fermentation and Shattered Bottle:
(i) Glucose Fermentation:
C6H12O6 (aq) -> 2C2H5OH (aq) + 2CO2 (g) (Glucose ferments to ethanol and carbon dioxide)
(ii) Shattered Bottle:
Fresh palm wine undergoes fermentation by yeast. During fermentation, yeast consumes sugar and produces carbon dioxide gas. In a tightly sealed bottle, the CO2 gas gets trapped and builds up pressure. As pressure increases, the glass bottle can no longer withstand the force and shatters.
(c) Metal Reactivity:
(i) Increasing Reactivity: K > Na > Fe > Cu
(ii) Reacting with Cold Water: K, Na (These alkali metals react vigorously with water)
(iii) Colored Salts: Cu (Copper forms characteristic colored salts, like blue copper sulfate)
(d) Redox Reactions and Half Reactions:
(i) Redox Reaction:
A redox reaction is a type of chemical reaction where there is a transfer of electrons between the participating atoms or ions. Oxidation is the loss of electrons, and reduction is the gain of electrons.
(ii) Identifying Redox Reactions:
- Redox: (II), (V)
- Not Redox: (I), (III), (IV)
(iii) Explanation for Redox Reactions:
- (II) AgCl + 2NH3 -> [Ag(NH3)2]Cl:
- Silver (Ag) loses an electron to become Ag+ (oxidation).
- Nitrogen (N) in ammonia gains an electron to form the complex ion [Ag(NH3)2]+ (reduction).
- (V) 2FeCl3 + 2KI -> 2FeCl2 + 2KCl + I2:
- Iron (Fe) in FeCl3 loses an electron to become Fe2+ in FeCl2 (oxidation).
- Iodine (I) gains an electron to form I2 (reduction).
(iv) Balanced Half Reactions (Examples):
- Oxidation Half Reaction (from reaction II):
Ag -> Ag+ + e-
- Reduction Half Reaction (from reaction V):
I- -> I2 + e- (Note: I- needs to be balanced with Cl- from the reactant side)
