The Stack Overflow podcast is back! Listen to an interview with our new CEO.
32

It's a very general statement, but it's not always true. I'll explain why it's often true, and give a counter-example at the end. Your majority component B and the impurity (let's call it A) form a binary system. In most cases, such binary mixtures exhibit a solid–liquid phase diagram as follows: (image taken from these lecture notes). This binary phase ...


20

(I'm no chemist, but here's my take on it) Let's see: I’m an alcoholic, and I really hate having to dole out large amounts of cash to purchase your usual "drinking"-ethanol. So I get this amazing idea to separate the ethanol by distillation (methanol has a lower boiling point than methanol, so what I'll really be doing is distilling out the methanol, ...


19

Thermodynamically, you're considering the chemical potentials ($\mu$) of the liquid and solid(s), specifically the temperature where they're equal. In a mixture, the potential is lower as the disorder (entropy) has increased, so all things equal, it will favor the liquid over a purer solid where there can be more disorder. Chemical systems seek to lower ...


17

There's a NASA report that looks into this: "ON THE SOLUBILITIES AND RATES OF SOLUTION OF GASES IN LIQUID METHANE", Hibbard and Evans, 1968 and concludes that such mixtures are possible. Starting on page 8: Figure 5(a) presents the curves for oxygen, argon, carbon monoxide, and nitrogen. Also shown are the two experimental values for nitrogen. ...


16

The short answer is: yes, this is possible. Unfortunately, solubility is a fairly complex phenomenon to explain simply. Let's start with some examples where solubility is higher in a binary mixture than either solvent alone. For a solid-liquid-liquid example: phenanthrene-cyclohexane-diiodomethane.[1] For a liquid-liquid-liquid example like the one you were ...


15

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†. This is what steam distillation is all about. As for the first law, it will hold just fine. You burn your firewood, you get the heat, but it is not for free: ...


13

Wikipedia already offers a decent summary of two theories of shear thickening behavior - namely the generation of transient 'defects' in a high-density suspension that either resist further growth or are incompressible in the direction of shear. A potential macroscale analogue of shear thickening is the dramatic increase in viscosity of large particle-air ...


13

Homogeneous and heterogeneous classifications are scale-dependent. What we mean when we say a mixture is homogeneous is that there are no visible phase differences on the scale of interest. For example, milk (when homogenized) and lotions are both examples of colloidal suspensions. There are no phase differences at the human scale, but neither one is a ...


12

The enthalpy is not additive under isobar, adiabatic conditions for non-ideal mixtures. The change in the enthalpy is called the excess enthalpy (enthalpy of mixing). It can be computed with models such as the Margules, van Laar, Wilson, NRTL, and UNIQUAC. These model give equations for the excess Gibbs energy. The excess enthalpy can be derived from these ...


10

The reason criminals don't undenture alcohol is probably because it's cheap and easy to make your own alcohol at home. Plus it's legal in the US (click on G1) and most other English-speaking countries. You can get equipment kits from anywhere between 50 and 200 USD (more expensive kits will get you tools that make things easier or improve quality and add ...


10

In Soviet Russia, where alcoholism was widespread and homebrewing illegal, undenaturing alcohol was a pretty common thing - a part of national culture, in a way - along with such practices as: drinking straight down various non-food grade products containing ethanol or extracting ethanol from them or stealing ethanol from industrial processes or, well, ...


9

General estimates have placed a can of Coca-Cola to have 2.2 grams of $\ce{CO2} $ in a single can. As a can is around 12 fluid ounces, or 355 ml, the amount of $\ce{CO2}$ in a can is: $$\text{2.2 g} \ \ce{CO2}* \frac{\text{1 mol} \ \ce{CO2}}{\text{44 g} \ \ce{CO2} } = 0.05 \ \text{mol}$$ $$ \text{355 mL} * \frac{\text{1 L}}{\text{1000 mL}} = 0.355 \ \text{...


9

As I mentioned in the comments, a quantitative separation of the three compounds will probably not be possible outside of a proper laboratory, however a coarse separation is possible. A quick search on the internet yields this link for the separation of $\ce{NaCl}$ and $\ce{KCl}$. You didn't give us the exact composition of the table salt substitute, so I ...


9

This question has a simple, but non-obvious answer. DMSO and water are miscible. Mixtures, and in particular homogeneous ones like that formed by water and DMSO, usually have lower melting (or more relevant in this case, freezing) points than either substance does alone. This is the reason salt melts ice: the salt solution has a lower freezing point than ...


9

To add to the Bob's excellent answer (and expand a bit on my comment there), I've found two other potentially interesting papers to peruse. The first is R.J. Hodges and R.J. Burch, Cryogenics 7 112-113 (1967), titled "The equilibrium distribution of methane between the liquid and vapour phases of oxygen". They note a "very high solubility of methane in ...


8

The textbook answer for why water can't mix with oil is to use the rule 'like dissolves like'. But a rule in science is none other than summarizing a few collected facts. Answering a question with a rule is like pointing a single fact - why water can't mix with oil - to a collection of facts instead. This easily invites a follow-up question, why like ...


8

The basic answer is that water molecules attract each other and so clump together forcing almost all of the oil out of the clump. The attraction exists because water is a polar molecule. That is, it has a positive end and an negative end. Thus the molecules tend to clump together just as a bag of small magnets tend to clump together. Oils, on the other ...


8

According to IUPAC gold book: A solution is a liquid or solid phase containing more than one substance... So, the concept "solution" is reserved to solid and liquid phases. In gas phase: Air is an example of homogeneous mixture of nitrogen, oxygen, carbon dioxide and other gases present in air. It's obvious that air is not a solution.


8

Milk is an emulsion containing small bubbles of oil/fat. Whenever you boil milk or do something drastic, this fat tends to separate. You can do this nicely, and get cream or butter, preserving the bubbles, only part of the water content is separated, or can do more drastically, when these bubbles collapse to a big oily blob. When you put your filter in the ...


8

In a binary homogeneous mixture, the component present in the larger amount is generally called the "solvent". The component present in the smaller amount is generally the "solute". In your first example, however, it is more complicated as coffee is already a complex solution (but mainly water). Milk is not a homogeneous mixture. It is a fat/protein ...


8

Nothing special would happen, immiscible liquids would just form layers. As for the expression, $$p_T=\Sigma p^o_i$$ I suggest you read this answer. Quoting Ivan Neretin: This is not just some vapor pressure. This is the equilibrium vapor pressure. Thermodynamics is all about equilibrium, you know. And equilibrium, roughly speaking, is what takes place ...


7

Two sources: water and natural flavors According to the Wisconsin department of healt natural sodium levels in water is $\pu{40-60 mg/L}$ meaning a $\pu{20 fl oz (\! 591 mL)}$ Coke has about $\pu{25 mg}$ of sodium from water. Thus the other $\pu{50 mg}$ of sodium must come from natural flavors. This makes sense since Coca-Cola uses plant products like coca ...


6

The Reynolds Number is the ratio of inertial to viscous forces and is calculated according to this equation: $$Re = \frac{\rho v L}{\mu}$$ where $\rho$ is the density, $\mu$ is the dynamic viscosity, $v$ is the fluid velocity and $L$ is a characteristic length that depends on the flow being modeled. When estimating the Reynolds number of a mixture, the term $...


6

The two above answers are academic/scholastic. I'll give an intuitive one. When impurity is in a solid, it usually (not always, as said in Answer 1) weakens the connections/forces between molecules, and hence makes it more vulnerable to heat (read lower melting point). A solid is like an army in rank and file. When you put a civilian in the army, it doesn't ...


6

As Ali said, unless the mixture is ideal the enthalpy of mixing (or excess enthalpy) is not zero. This is the basis for a whole field of thermodynamics (and in particular, statistical thermodynamics): solution theories. To quote only a few of the most famous ones: VST (Vacancy Solution Theory) [I don't have a good reference at hand right now, I'll try to ...


6

Here are some similarities: There is always a mobile (e. g. Gas - GC, Liquid - HPLC; GPC) and a stationary phase (liquid; gel - GC, solid - LCs, GPC). Compounds in the sample interact different with both phases and are therefore held back stronger or lesser. This results in the accumulation of compounds that interact similar at some point in the system $-$ ...


6

Strictly speaking you might have a point there. But it is probably more difficult to judge. I was unable to unearth an official recommendation by the IUPAC, so I unfortunately have resort to Wikipedia ([1] Kristi Lew (2009). Acids and Bases. Essential Chemistry. New York: Chelsea House Publishing.): Homogeneous is a term in physical chemistry and ...


6

Typical vegetable oils are not just one chemical compound, but a mixture (after removing everything that is not) of glyceride triesters. The chance that there is some overlap between your two oils is big, so the answer to your immediate questions likely is no, completely impossible. Even if there is no overlap in the chemical composition, you would probably ...


5

I just thought I'd add a visualisation of this concept. Electrostatic maps show the electrostatic potential at a given point of the molecule. We know water is very polar, and this is evident from its electrostatic map: If we look at octanol though, we see that the vast majority of the molecule is non-polar (evenly distributed electrostatic charge): The ...


5

This is a difficult question to answer without having specific compounds to work with, but let's say that you have a pair of enantiomers with a single stereocenter, so there's an (R)-enantiomer and an (s)-enantiomer. There are four possible reactions: $\ce{R + R -> RR}$ $\ce{R + S -> RS}$ $\ce{S + R -> SR}$ $\ce{S + S -> SS}$ The set of ...


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