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48 votes

What is the pH of ice?

According to Martin Chaplin's Water Dissociation and pH: In ice, where the local hydrogen bonding rarely breaks to separate the constantly forming and re-associating ions, the dissociation constant ...
DavePhD's user avatar
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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 ...
ACR's user avatar
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46 votes
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Is there a cheap, safe liquid that evaporates EXOthermically around room temperature?

No such liquid, safe or otherwise, can exist. Evaporation is a strictly endothermic process in all cases. The change in state from liquid to gas is marked by the individual particles gaining enough ...
hBy2Py's user avatar
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36 votes

How does water evaporate completely when at room temperature?

As your small percentage of molecules with high enough kinetic energy evaporates, the remaining liquid water cools down. But in doing so, it drains heat from its surroundings and thus stays at room ...
Ivan Neretin's user avatar
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34 votes
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A glass of water with ice-cubes in it. Where's the water the coldest; at the top or bottom?

Interesting question! A few things first: As the ice melts, it cools the water around it. Technically, the ice cube melts because the water cools down. This may sound ridiculous at first, but you ...
paracetamol's user avatar
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28 votes
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At what pressure will hydrogen start to liquefy at room temperature?

$\ce{H2}$ cannot be liquified at room temperature, whatever the pressure. Generally speaking, all gases can only be liquified when the temperature is under its critical value.
Maurice's user avatar
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24 votes

At what pressure will hydrogen start to liquefy at room temperature?

The critical temperature of Hydrogen is $\pu{32.938 K, resp. -240.21 ^{\circ}C}$. Above this temperature, it cannot be liquified. So to answer your question, you can get as high pressure as you can ...
Poutnik's user avatar
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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
17 votes

What is the pH of ice?

$\mathrm{pH}$ is the aqueous concentration of $\ce{H3O+}$ or $\ce{H+}$ ions in soution. I would not say that ice lacks $\ce{H3O+}$ and $\ce{OH-}$ ions as ice's structure would allow for such, however, ...
A.K.'s user avatar
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16 votes

Why does ice crack when a drink is poured on it?

I believe the ice cracked due to residual strains from freezing. Since ice freezes from the outside inward and it expands as it freezes, that as the inner water freezes, it imparts a tensile force on ...
A.K.'s user avatar
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16 votes

Is it possible to boil a liquid by just mixing many immiscible liquids together?

Yes they will boil all right. Sure, there might be some kinetic impediment to it if you let the liquids to settle in layers, but if you stir them so as to expose their surfaces, they will boil†....
Ivan Neretin's user avatar
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16 votes

Why does gas not liquify at a temperature above the critical temperature no matter how much pressure is applied on it? Why?

The critical point is a point of convergence of all state properties of the respective liquid and gas. It can be considered as the degeneration point, where there is no difference between gas and ...
Poutnik's user avatar
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15 votes
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Is oxygen above the critical point always supercritical fluid? Would it still appear to roughly follow the ideal gas law?

Yes. Any fluid with a temperature is above critical temperature and the pressure above the critical pressure is by defintion a supercritical fluid. Don't be mislead by all the claims that ...
Curt F.'s user avatar
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15 votes
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Are molecules exchanged between a solid and liquid in equlibrium?

Even two solids in contact may exchange atoms, such as gold in contact with lead. Accidental cold-welding is a serious problem in space technology, in particular. You can prove to yourself that ice/...
DrMoishe Pippik's user avatar
14 votes
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Why does liquid water form when we exhale on a mirror?

Why do we have water vapors when our body temperature is also <100°C in the first place? At normal pressure, water boils at 100°C, meaning that bubbles of pure steam form under water. At lower ...
Karsten's user avatar
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14 votes

Why does gas not liquify at a temperature above the critical temperature no matter how much pressure is applied on it? Why?

It really does liquefy. But it does not do so in exactly the same way as you see below the critical temperature and pressure. As an example, suppose you heat steam to 400°C and then compress it, ...
Oscar Lanzi's user avatar
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13 votes
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Freezing point of oxygen-18 water

In this paper [1] from 1963, various properties of heavy-oxygen water are measured including the melting point of both $\ce{H2^{18}O}$ and $\ce{D2^{18}O}$. The melting temperatures were measured at: $...
jheindel's user avatar
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12 votes
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What phase of matter is shaving cream?

Shaving cream is a special type of mixture called a colloid, consisting of tiny air bubbles dispersed in liquid. This particular type of colloid can further classified as a foam. Since the mixture ...
ringo's user avatar
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12 votes

Does naphthalene in moth balls really sublimate or does it evaporate?

Naphthalene, as well as any other solid, may sublimate at any temperature and pressure. The triple point parameters are irrelevant. The pressure of other components (that is, air) is irrelevant as ...
Ivan Neretin's user avatar
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12 votes

A glass of water with ice-cubes in it. Where's the water the coldest; at the top or bottom?

The convection to produce uniformity depends on a number of nebulous factors: How much ice? How tall is the glass? Diameter of the glass? Is the "glass" really a glass or paper cup, styrofoam cup, ...
MaxW's user avatar
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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
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12 votes
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What would oxygen or nitrogen snow look like?

I don't know if there would actually be oxygen and nitrogen snow. I would think under those circumstances, there might be carbon dioxide snow, but the rest of the atmosphere would probably liquify ...
Gwyn's user avatar
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12 votes

Do all three states need to be present at triple point?

Writing an answer because it's too large to be a comment, but it is rather indirect. I'm quite convinced the correct (or "most correct") answer is D, because it is "simple", while ...
Nicolau Saker Neto's user avatar
11 votes
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Can I pour a solution into another vessel with no air bubbles?

There are two aspects to consider for the intended "air bubble free" (or at least, "air bubble less") transfer from your container where the liquid is prepared into the container where the liquid is ...
Buttonwood's user avatar
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11 votes
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Why does ordinary water have a triple point?

Summarizing the relevant point (pun intended) of my answer to a related post: a mixture does not exhibit a "triple line" if its composition is constant. It is only a "triple line" ...
Buck Thorn's user avatar
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10 votes
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Significance of phase of atomic orbitals

You have quite a few questions indeed! What is the significance, if any, of the phase of the wavefunction for electrons in atoms when the atom is not interacting? Suppose you had a free hydrogen ...
orthocresol's user avatar
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10 votes
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What is the physical state of a single atom?

This answer has been written so it hopefully can be understood by people that do not have a degree. If something is not correct, let me know, but be aware that throwing around fancy words will not ...
Raditz_35's user avatar
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10 votes

Why does liquid water form when we exhale on a mirror?

The major difference is that in vapor phase, the water can leave the container (so you can tell it's in a different form), and which prevents it from immediately rejoining the liquid. In both solid/...
BowlOfRed's user avatar
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10 votes
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Why is the molar entropy of hexane lower than that of butane?

There are two factors to consider. Certainly, the dominant factor is that the degrees of freedom available for the molecule to disperse energy into increases as the carbon chain extends. Thinking ...
jezzo's user avatar
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