48 votes

Which "exotic salt" can lower water's freezing point by 70 °C?

I recently got a chance to attend a talk by someone who was working on developing analytical instrumentation on Mars. The interesting story is that the initial results by ion-selective electrode was ...
AChem's user avatar
  • 40.2k
20 votes

Which "exotic salt" can lower water's freezing point by 70 °C?

Your Question: Which "exotic salt" can lower water's freezing point by $\pu{-70 ^\circ C}$? Here is your "exotic compound" although it is not a salt by definition. It is a base: Aqua ammonia, also ...
Mathew Mahindaratne's user avatar
15 votes

How much salt (or any other substance one can find in a kitchen) do I need to add to make water boil at 104 °C?

According to [1, pp. 281–282], solution of sodium chloride $\ce{NaCl}$ prepared by dissolving 25 g of salt in 100 g of water has boiling point of 104.6 °C. Additional data is available in the ...
andselisk's user avatar
  • 37.7k
13 votes
Accepted

The connection of the "R" in the ideal gas law and osmotic pressure

It's not a coincidence at all! If you do an online search for "derivation of osmotic pressure", you'll see how $R$ enters into the derivation. Indeed, that's one of the beauties of the van 't Hoff ...
theorist's user avatar
  • 12.1k
12 votes

Which "exotic salt" can lower water's freezing point by 70 °C?

Magnesium perchlorate is far from unique. In fact, if you're willing to spend a little money at that hardware store you could pick up some calcium chloride, whose eutectic reaches about -50°C, not ...
Oscar Lanzi's user avatar
  • 57.1k
7 votes
Accepted

What happens to the gas inside cold drinks as the cold drink is frozen?

Well, you are certainly right in that the solubility of the gas will grow if you decrease the temperature, and so it will continue all the way down to the freezing point. That's when things get hairy. ...
Ivan Neretin's user avatar
  • 31.2k
6 votes
Accepted

Intuitive explanation for depression of freezing point

Imagine a pure liquid. If part of it freezes, what happens to the rest of the solution? Well, it looks exactly the same since it's also pure, so nothing. However, this is not true for the system you'...
Zhe's user avatar
  • 17.4k
5 votes

Intuitive explanation for depression of freezing point

Here is a - hopefully intuitive - explanation based on kinetics: I start with a glass of water with ice cubes in it, sitting outside in winter on a day where the temperature happens to be equal to ...
Karsten's user avatar
  • 40.2k
5 votes
Accepted

Do colligative properties depend on the number of solute molecules?

It's not good notation on the TAs part. IUPAC defines a molecule as having to be electrically neutral. I see what they are intending, but solute particles would be more correct. This is why, as you ...
Tyberius's user avatar
  • 11.7k
5 votes

Detailed kinetic explanation for vapor pressure reduction by dissolved solute?

I'd like to specifically commment on this: According to the NCERT for Class XII, Part I, [pg. 46, para 3][1], In a pure liquid the entire surface is occupied by the molecules of the liquid. If ...
theorist's user avatar
  • 12.1k
4 votes

Relative lowering of vapour pressure

In the simplest terms and most convenient definitions, the lowering of vapor pressure is not a colligative property while the relative lowering of vapor pressure is indeed a colligative property. A ...
MasterYoda's user avatar
4 votes
Accepted

How do repulsive solute interactions affect the van't Hoff factor?

I think that your first probabalistic argument is correct, i.e that as the solute interaction increases the effective number of them is reduced. In the second case, as the interaction become repulsive,...
porphyrin's user avatar
  • 30.5k
4 votes
Accepted

Why it is very rare to find a compound that lacks carbon to be liquid at standard temperatures and pressures?

The property of carbon that causes this is the ability to form rings and chains that are stable under atmospheric conditions. The only reason why ‘so many liquids contain carbon’ is basically ...
Jan's user avatar
  • 68k
4 votes

Why do colligative properties depend only on number of solute particles?

It's a lie. Colligative properties do depend on the chemical nature of the solute and solvent - their interaction. The trick is: an ideal solution, in which the solute-solute intermolecular forces and ...
Vinícius Godim's user avatar
4 votes
Accepted

Boiling point elevation with multiple solutes

When there is more than $1$ solute in the solution, the total elevation in boiling point ($\Delta T_\mathrm{b,total}$) or the depression in freezing point ($\Delta T_\mathrm{f,total}$) is defined as ...
Safdar Faisal's user avatar
4 votes
Accepted

Why is the boiling point of sugarcane juice lower than the boiling point of water?

A more plausible explanation is that it is not water that is boiling. The "organic substances" and maybe the "nitrogenous substances" in the juice could include some more ...
Oscar Lanzi's user avatar
  • 57.1k
3 votes
Accepted

Why do colligative properties depend only on number of solute particles?

A very simple, qualitative explanation: After your solute has dissolved, there are no more enthalpic effects to take into account. The solvation enthalpy is converted to a temperature change, and ...
Karl's user avatar
  • 12.1k
3 votes

Deviations from Raoult's Law

For most solutions, it is nearly impossible to predict in advance whether a positive or negative deviation is observed. A deviation from Raoult's law can only be measured experimentally. However, for ...
Mehul Arora's user avatar
3 votes

Why do we use molality on describing colligative property?

Molality is a useful unit in colligative properties because it is independent of temperature, it is not affected by volume changes upon mixing and it will allow you to calculate mole fractions. Keep ...
AChem's user avatar
  • 40.2k
3 votes
Accepted

The relationship of the osmotic pressure of a polymeric solution and its the molecular mass

The statement is true if the mass concentration (e.g., $\pu{g//L}$) of polymers in solution is constant, but false if the number concentration (e.g.,$\pu{mol//L}$) of polymers in solution is constant. ...
theorist's user avatar
  • 12.1k
2 votes

Relationship between freezing point depression and hydrogen bonds

The addition of one molecule (or salt) of solute produces $i$ effective solute particles. This defines the van't Hoff factor $i$, which encodes the strength of the solute with regards to colligative ...
a-cyclohexane-molecule's user avatar
2 votes
Accepted

How to approximate the pH of a box of water molecules with one proton?

For a rough, back of the envelope, sanity check sort of calculation, your second approach is more appropriate than the first. (Though check your value for Avogadro's number.) This is something that ...
R.M.'s user avatar
  • 4,884
2 votes

How to calculate the depression in freezing point of a solution in which there are multiple solutes being added?

Freezing point depression is a colligative property, well defined by this Wikipedia article (emphasis mine): In chemistry, colligative properties are properties of solutions that depend on the ratio ...
airhuff's user avatar
  • 17.5k
2 votes

Depression of freezing point

You argument is largely based on enthalpy, whereas freezing point depression and boiling point elevation is (in the situation when the solute only weakly interacts with the solvent) mainly an entropic ...
Ivo Filot's user avatar
  • 1,404
2 votes

Why does freezing point decrease when vapour pressure decreases in dilute solutions?

Consider graphs of the vapor pressure of the liquid and of the solid, both as a function of temperature. Intuitively, both graphs increase with temperature, and intersect at the freezing point. By ...
a-cyclohexane-molecule's user avatar
2 votes

Colligative properties of colloids

Roughly (in the ideal world), colligative properties depend on the number concentration of particles, not on what those particles are. A particle can be a micelle or vesicle or other colloidal ...
Buck Thorn's user avatar
  • 21.7k
2 votes
Accepted

Elevation in boiling point of water

While considering colligative properties we always assume solute to be non-volatile. So, it doesn't contribute to the vapor. The amount of vapor will only be due to solvent particles. So, in the ...
Fancy-Toon's user avatar
2 votes

Freezing Point Depression and Temperature Decrease

First of all, it is useful to envision an adiabatic process: add ice at the normal melting temperature to water or cold brine slightly above the MP in a perfectly insulated container (zero heat ...
Buck Thorn's user avatar
  • 21.7k
2 votes
Accepted

Freezing Point Depression and Temperature Decrease

Phase change is not at constant temperature, phase equilibrium is [OP] it's a phase transition so the temperature of the ice should remain constant Here is a counter example: If you add ice cubes ...
Karsten's user avatar
  • 40.2k

Only top scored, non community-wiki answers of a minimum length are eligible