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Is toothpaste solid or liquid?

Toothpaste is what is called a non-newtonian fluid, more specifically toothpaste is a Bingham plastic. This means that the viscosity of the fluid is linearly dependent on the shear stress, but with ...
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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 ...
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47 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 ...
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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 ...
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44 votes

Is toothpaste solid or liquid?

Here's a genchem-level answer for a genchem-level question about the classification of matter: Toothpaste is a sol: a stable suspension of tiny solid particles in a liquid. When the toothpaste dries ...
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35 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 ...
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33 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 ...
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28 votes
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What happens if you cool water in a container too small for it to freeze?

Good question. Let's assume the container is infinitely strong, non-deformable, and constant in volume. Let's also assume that cooling the water is an equilibrium process -- that way, we won't have ...
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26 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.
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25 votes
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Molten vs Liquid

As you said, the meaning is exactly the same. Molten reduces the ambiguity, because you emphasize that you know, that it is solid substance at laboratory conditions and you heat it to become liquid (...
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23 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 ...
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22 votes

Is toothpaste solid or liquid?

Here's the boring answer: Toothpaste is a mixture of some solids and some liquids. The question "is it solid or liquid?" makes sense when you're talking about a substance or a mixture with a single ...
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22 votes
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Burns from boiling water and steam

Let’s consider the following cases: getting $1\,\mathrm{mol}$ of $100\,\mathrm{°C}$ water on one’s skin getting $1\,\mathrm{mol}$ of $100\,\mathrm{°C}$ air on one’s skin getting $1\,\mathrm{mol}$ of $...
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21 votes

How many molecules does it take to have a phase?

This is actually an active area of research for water clusters. In principle, for $\ce{(H2O)_{n}}$ there should be a "melting" phase transition, much like for ice to liquid water. So, in ...
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21 votes
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Why can't helium be solidified at 'ordinary' pressures?

When the temperature of helium gas is decreased to about 5.2 K, a phase transition to ordinary liquid helium ($\ce{He}$ I) occurs. The behavior of this liquid phase is normal and identical to any ...
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20 votes
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Why is active mass of a pure solid or liquid always taken as unity?

Does the activity of a solid or liquid change over the course of a reaction? The density of a solid or liquid reactant doesn't change over the course of a reaction. The mass and volume do as it is ...
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20 votes
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Why must both the critical temperature and pressure be exceeded to achieve the supercritical phase?

The critical point is a phase transition of phase transitions. It's a different beast than your everyday run-of-the-mill phase transition like water boiling to vapor or ice melting to water. The ...
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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 ...
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16 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, ...
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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 ...
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15 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 ...
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15 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†....
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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 ...
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14 votes

Is toothpaste solid or liquid?

It is Viscous. Viscous mean "having a thick, sticky consistency between solid and liquid"(dictionary meaning) There are many more examples like tomato ketchup, honey, wax, toothpaste, etc. To know ...
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14 votes

Is toothpaste solid or liquid?

Toothpaste is a colloid. just like dust particles suspended in water form suspension, colloids are much finer particles suspended in a medium. for example jelly, it is solid particles suspended finely ...
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14 votes
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Why does HCN boil at a higher temperature than NH3?

The enthalpy of vaporization of $\ce{HCN}$ is higher than for $\ce{NH3}$, which suggests that $\ce{HCN}$ molecules interact more strongly than $\ce{NH3}$ molecules. $\ce{C-H}$ bonds are not usually ...
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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 ...
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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, ...
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13 votes
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During phase change in matter, why doesn't the temperature change?

From Changes of Phase (or State): ... So, how could there be a change in heat during a state change without a change in temperature? "During a change in state the heat energy is used to change the ...
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