Which will freeze the fastest in water salt sugar or baking soda?

Answer 1

The question is not worded well because the salt or sugar or baking soda in the water doesn't itself freeze. The whole solution freezes.

But I understand what you're asking, and there is not really enough information to answer the question.

IF:

(1) The number of moles of water and the number of moles of the three solutes added to the water is the same for each respective solution.

AND

(2) Each solution is cooled at the same rate.

The answer would be that the sugar water would freeze faster.

The reason why:

Freezing point depression is a collagitave property. It depends on the number of (not the nature of) the dissolved particles.

In other words, the amount the freezing point of water is depressed (lowered) is proportional only to the number of moles of dissolved particles, whether the dissolved particles are ions from salt or big molecules from sugar.

One mole of sugar dissolves to give one mole of aqueous sugar molecules.

One mole of baking soda, however, will give one mole of aqueous Na+ ions AND one mole of aqueous HCO3- ions, which gives twomoles of dissolved particles overall.

Salt is similar to baking soda 1NaCl (s) --> 1Na+ (aq) + 1Cl- (aq), yielding two moles of solvated particles for each one mole of salt added.

Thus the salt and baking soda will lower the freezing point of water more than sugar will (again, provided you add the same number of moles) and thus the sugar water will freeze at a higher temperature than the salt or b.s. water.

If you want to demonstrate this in an experiment, molar mass must be taken into account here, because same mass/weight/volume does NOT mean same number of moles.

Salt and baking soda have a much lower molar mass than sugar, so even a little salt will produce more dissolved particles than a lot of sugar.

This stuff is covered briefly at the end of most college chemistry courses. They also deal with the question of which would boil faster and other questions.

Look up "freezing point depression" and "collagitive properties."