To determine the order of decreasing freezing points for the given aqueous solutions, you need to consider the concept of freezing point depression.
Freezing point depression is a colligative property that depends on the number of solute particles present in a solution, rather than the identity of the solute. The greater the concentration of solute particles, the lower the freezing point of the solution compared to the pure solvent.
In this case, we have five aqueous solutions: 0.10 m Na3PO4, 0.35 m NaCl, 0.20 m MgCl, 0.15 m C6H12O6, and 0.15 m CH3COOH.
First, let's count the number of solute particles for each compound by determining the number of dissociated ions (if applicable) or individual solute particles. This will give us an idea of the resulting freezing point depression.
1. Na3PO4:
Na3PO4 dissociates into three Na+ ions and one PO4(3-) ion, giving a total of four solute particles.
2. NaCl:
NaCl dissociates into one Na+ ion and one Cl- ion, giving a total of two solute particles.
3. MgCl:
MgCl does not dissociate, so it remains as one solute particle.
4. C6H12O6 (glucose):
C6H12O6 remains as one molecule, so it also remains as one solute particle.
5. CH3COOH (acetic acid):
CH3COOH can partially dissociate into H+ ions and CH3COO- ions. However, since the concentration is relatively low (0.15 m), we can consider that it remains mainly as one molecule and therefore one solute particle.
Now let's arrange the solutions in order of decreasing freezing points based on the number of solute particles:
1. Na3PO4 (four solute particles)
2. NaCl (two solute particles)
3. MgCl (one solute particle)
4. C6H12O6 (one solute particle)
5. CH3COOH (one solute particle)
So, the correct order of decreasing freezing points (lowest to highest temperature) for the given solutions is:
Na3PO4 < NaCl < MgCl < C6H12O6 = CH3COOH