Dalton's Law of Partial Pressures Lecture Demonstrations
Draw 4 mL of any gas (A) into a 10 cc syringe (a colored gas such as nitrogen dioxide is ideal, but not necessary). Draw 6 mL of a second gas (B) into the syringe. See Graham's Law of Diffusion Lecture Demonstrations#Graham's Law of Effusion for convenient means of handling gases.
Now, for the two gases in the syringe,
1. What is the volume of A?
- (10 cc) (all gases expand to fill their containers).
2. What is the volume of B?
- (10 cc)
The amounts of the two gases cannot be distinguished by their volumes!
3. What is the pressure of A, since it expanded from 6 to 10 mL?
Boyle's law tells us:
(1Atm)(6 mL) = PB (10 mL)
- P2 = 0.6 Atm
4. What is the pressure of B?
Dalton's Law tells us: If the pressure of A is 0.6 Atm, and the total pressure is 1.0 Atm, the pressure of B must be 0.4 Atm.
5. Use Avogadro's Law to derive other useful forms of Dalton's Law.
PA / Ptot = nA / ntot