B.Sc. chemistry lead silver system ZINC CADMIUM SYSTEM phase rule phase diagram TY SEMESTER 5 & 6

1. LEAD-SILVER SYSTEM
CECH-509
UNIT-4(B)
BY – Ms MAYURI R SOMPURA
HJD INSTITUTE - KUTCH

2. • These metals are completely miscible in liquid state.
• They do not form any compound together.

4. • Pure lead melts at 327℃.
• Addition of silver lowers its melting point.
• Pure silver melts at 961℃.
• Addition of lead lowers its melting point.
• Along AB solid lead and solution (melted) is present.
• Along BC solid silver and solution (melted) is present.
• System is monovariant among AB & BC.

5. B is the eutectic point where three phases solid lead, solid silver and
both their liquid forms si present.
The temperature of eutectic point is 303 ℃.
Composition of the solution phase is 2.6% silver.

6. • the phase diagram of Pb-Ag system has special significance in
connection with the ‘derivation of lead’.
• The argentiferous lead consisting of a very small percentage of silver
is first heated to a temperature well above its melting point.
• So, system only consists of the liquid phase represented by point a’’in
the figure.

7. • It is then allowed to cool.
• As soon as the point a’ is reached, lead will began to crystallize and
solution will contain relatively increasing amount of Ag.
• Further cooling will shift line along a’a .
• Lead continues to separate out and is constantly removed from the
melted solution.

8. • The melted liquid will constantly become richer and richer in silver
until point a is reached, where the % of Ag rises to 2.6%
• Thus, the original argentiferous lead which might have contained 0.1%
or less of silver can now contain upto 2.6% of Ag.
• This process is known as ‘Pattinson’s process’.

9. assignment :-
1. Explain two component system with the reference of Pb-Ag system.

10. ZINC-CADMIUM SYSTEM
CECH-509
UNIT-4(B)
BY – Ms MAYURI R SOMPURA
HJD INSTITUTE - KUTCH

12. • Pressure is kept constant at 1.0 atm.
• Degree of freedom is decreased by 1.0.
• The reduced phase rule ( F = C – P + 1 ) is used.
• No compound is formed in this system.

13. • Point A shows the melting point of pure zinc.
• When Cadmium is added the melting point of Zn is decreased along
AO.
• B is the freezing point of pure cadmium.
• When Zn is added the freezing point decreases along BO.

14. • We get minimum melting point at O, when three phase are in
equilibrium – solid Zn, solid Cd and liquid.
• This is the eutectic point.
• The eutectic mixture contains 17% Zn and 83% Cd.

15. assignment :-
1. Explain two component system with the reference of Zn-Cd system.