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31
votes
2answers
160k views

What do the different grades of chemicals mean?

When purchasing chemicals from Sigma, Fisher, or wherever, there are often -grade's attached to their description like reagent-grade, technical-grade, analytical-grade, or more niche-sounding biotech-...
31
votes
2answers
2k views

What makes ice slippery?

I've heard and read (multiple times) two theories have have been around for a while, both of them obvious nonsense. One states that pressure and friction make the ice melt (turn to water) where the ...
31
votes
1answer
16k views

Relative stability of cis and trans cycloalkenes

Why is the stability of (Z)-cyclodecene 2 greater than that of (E)-cyclodecene 1? I'd think that since 1 contains a trans double bond instead of a cis double bond, it should experience less steric ...
31
votes
2answers
2k views

What makes Gorilla Glass more durable with each generation?

Gorilla Glass (GG) is one of the most recognizable brands of toughened glasses today, thanks to their marketing and widespread usage in various gadgets and automobile industry. According to Wikipedia,...
31
votes
1answer
20k views

Why does the unstabilised Wittig reaction selectively form cis alkenes?

This question is meant for a simple unstabilised ylide. The mechanism of the Wittig reaction, as given on ChemTube3d, involves a concerted formation of the oxaphosphetane (this is generally favoured ...
31
votes
5answers
18k views

Why are there only 7 types of unit cells and 14 types of Bravais lattices?

Why are there only 7 types of unit cells and 14 types of Bravais lattices? I was reading about solid-state chemistry for the first time and this limitation made no sense to me. I tried to do the ...
31
votes
1answer
4k views

In what way could benzoin give Tollen's test?

In Q29 of Joint Entrance Exam (JEE) 2016 India, the official answer key mentions that benzoin gives Tollen's test. However, I saw this post which says that it doesn't: Why do α-hydroxy ketones give ...
31
votes
1answer
15k views

Melting and boiling point trend in Group II

The following picture shows the melting and boiling point trends down group II elements. I have added question marks where the variability in data was rather disturbing (over two hundred degrees ...
30
votes
4answers
7k views

Why is '-ethane' in 'methane'?

Is there a chemical or historical significance in the fact that 'ethane' is just 'methane' without the 'm'?
30
votes
5answers
8k views

How do orbitals coexist with a nucleus?

Many diagrams of orbitals I've seen involve electrons moving through a center point—where the nucleus is. How can this be? Clearly they don't actually pass through the nucleus, so what does happen?
30
votes
2answers
55k views

What is the unit of pH?

I'm making some graphs and I have to label the axes. I want to be extra careful and put the units in even though the meaning of $\text{pH}$ is well known. But I have a problem (though a simple one): $\...
30
votes
4answers
242k views

Why do transition elements make colored compounds?

Why do transition metals element make colored compounds both in solid form and in solution? Is it related to their electrons?
30
votes
2answers
4k views

Is honey really a supersaturated solution? Does heating to un-crystalize redissolve it or melt it?

In the SciShow video Honey: Bacteria's Worst Enemy after about 00:30 the narrator says: Honey is only about 17% water. Most, but not all of what remains is sugar. ...
30
votes
1answer
4k views

How to name binary (inorganic) compounds given their chemical formula, and vice-versa?

I wish to understand how to name binary (inorganic) compounds when given their formula. When I am a given compound like $\ce{B2F2}$ or $\ce{N2O4}$, I have little to no clue on how to write their ...
30
votes
5answers
114k views

Difference between exothermic and exergonic

In High School I learned that an exothermic reactions releases energy, while an endothermic reaction needs energy to occur. Now I learned that there is a separate, somewhat similar classification ...
30
votes
3answers
4k views

Why don't gases escape Earth's atmosphere?

Some gases are lighter than others and rise. Why don't they continue going up, leave the atmosphere, and then enter outer space?
30
votes
2answers
5k views

What is the exchange interaction?

As the wikipedia article for the exchange interaction so aptly notes, exchange "has no classical analogue." How wonderful. Exchange shows up essentially while enforcing the condition that two ...
30
votes
3answers
5k views

Are graphite and hexagonal boron nitride aromatic

Are graphite and hexagonal boron nitride aromatic? Graphite has a planar network of 6-membered rings with each carbon connected to three other carbons. Since the valency of carbon is not satisfied, ...
30
votes
1answer
3k views

Unusual Friedel–Crafts alkylation with pivaloyl chloride

In class we were told of an anomalous Friedel–Crafts reaction with a tertiary acid chloride — $\ce{(CH3)3CCOCl}$, or pivaloyl chloride. When this reacts with benzene in the presence of $\ce{AlCl3}$, ...
30
votes
2answers
34k views

Why does the 3rd electron shell start filling up with scandium?

The electron configuration of calcium is 2, 8, 8, 2, where up to that point each shell, asides from the first shell counts up to 8 - why then does scandium have an electron configuration of 2, 8, 9, 2?...
30
votes
1answer
543 views

Imaginary Bonding Interactions

Usually in chemistry, we deal with bonding interactions. That is, if I have the diatomic A-A molecule or A-B molecule, there's a favorable interaction (i.e., a bond) and a prototypical MO diagram like ...
30
votes
1answer
667 views

d-orbital splittings in WS2 monolayer

The formerly degenerate $d$ orbitals of the tungsten atoms in the $\ce{WS2}$ monolayer are split into three groups: (1) $\mathrm{d}_{z^2}$, (2) $\mathrm{d}_{x^2-y^2}, \mathrm{d}_{xy}$ and (3) $\mathrm{...
29
votes
3answers
19k views

Which is the densest gas known?

Which is the densest gas known to exist under normal "shirt sleeve" conditions: room temperature, one atmosphere, won't explode on contact with air, won't kill everyone in the building in trace ...
29
votes
4answers
8k views

Is "stainless" a bulk or a surface property of stainless steel?

In particular, if I cut a block of stainless steel in half, would the newly formed faces be stainless as well?
29
votes
4answers
5k views

Is there radioactivity at absolute zero?

Theoretically, will a radioactive material still be radioactive at absolute zero? What would happen at the lowest realistic temperatures we have ever achieved? Will radioactivity stop at absolute ...
29
votes
2answers
4k views

How to properly store acids at home?

I bought different kinds of acid for experiments and home usage that I stored in secured containers into an IKEA cabinet. I just realized that despite the fact that all the containers are properly ...
29
votes
3answers
10k views

Why does chocolate melt so easily?

(Yes, I know the question sounds super-trivial... but bear with me here) Most chocolates (especially milk-chocolate) tend to melt into this sticky (albeit delicious) mess at temperatures slightly ...
29
votes
5answers
23k views

Microwaving a glass of water, what happens?

Most of us here would already know the simplified idea behind microwaving food: Microwave radiation hits the water molecules present in food, which excites them and causes 'em to vibrate rapidly in ...
29
votes
3answers
2k views

Why is 1-ethylidene-4-methylcyclohexane chiral?

As far as I can tell, there doesn't seem to be a chiral carbon in this compound. C-4 of the cyclohexane ring has two groups with exactly the same connectivity, and the exocyclic double bond can't give ...
29
votes
5answers
56k views

Why are tertiary carbocations the most reactive, if they're already stable?

This may seem silly, but doesn't it seem weird for a compound that's stable (in this context, the tertiary carbocation) to be the most reactive? I mean, wouldn't it be the least, given that it's ...
29
votes
3answers
30k views

What metals aren't dissolved in/attacked by aqua regia?

Aqua regia (Latin: Royal Water) is one of the strongest acids known in Chemistry, and is capable of dissolving gold and platinum. My copy of the Oxford science dictionary goes on to say (under the ...
29
votes
4answers
9k views

Why is the Vitamin B complex, a "complex"?

I often come across the term "Vitamin B Complex" in my biology classes and innumerable times on the back of multivitamin packets, but what does the term "complex" here, even mean? I'm still in high-...
29
votes
2answers
3k views

Why is −78 °C a magic temperature for organic reactions?

In many organic reactions that I have seen, running the reaction at $\mathrm{-78\ ^\circ C}$ seems to be quite a popular choice, but I've never seen any explanation for this. What makes this ...
29
votes
3answers
80k views

Is alcohol really a solution?

A friend recently sent me the following chemistry joke: As a lover of puns, I'd like to enjoy it, but I think that it is actually false the way it is phrased. A solution is defined as: "a ...
29
votes
4answers
10k views

Why are DCM and chloroform so resistant towards nucleophilic substitution?

In the book Organic Chemistry by J. Clayden, N. Greeves, S. Warren, and P. Wothers I found the following reasoning: You may have wondered why it is that, while methyl chloride (chloromethane) is a ...
29
votes
5answers
4k views

How 'heavy' should an element be, to be a "Heavy Metal"?

I've come across the term "Heavy metals" innumerable times in articles, mostly pertaining to environmental issues. Is there a weight range (of sorts) against which an element (metal) is classified as ...
29
votes
3answers
10k views

What substances do humans consume that are caloric but neither protein, carb, nor fat?

On the Medical Sciences StackExchange site I asked Can a calorie be neither protein, carb, nor fat? and got a very helpful answer, which was that ethanol (in alcoholic drinks) is caloric but neither ...
29
votes
4answers
9k views

Is activated carbon classified as organic or inorganic?

Organic compounds are typically defined as “molecules containing carbon”. Wikipedia states that there for some historical (read: non-logical) reasons, a few types of carbon-containing compounds ...
29
votes
1answer
3k views

Why is heroin a more potent drug than morphine, despite having a similar structure?

The structures of heroin and morphine are quite similar, with heroin being formed by acetylation of morphine: Why is heroin so much more potent than morphine, when their structures are so similar? ...
29
votes
4answers
48k views

Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?

Take for instance the reaction $$\ce{H2(g) + I2(s) <=> 2HI(g)}$$ The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a ...
29
votes
2answers
29k views

What is Drago's rule? Does it really exist?

My textbooks states the Drago's rule in inorganic chemistry as follows: The more electronegative atom prefers the orbital having more $\mathrm{p}$ character, and lone-pairs or less electronegative ...
29
votes
2answers
37k views

Why do atoms "want" to have a full outer shell?

Okay, so I know that this is about filling the orbitals of the atom, and I understand that. What I don't understand is why? For example, an Oxygen atom has 8 protons and 8 electrons spinning around it....
29
votes
1answer
17k views

Electrical conductivity of graphite

On this Wikipedia page, the electrical conductivity of various materials are given in the third column ($\sigma \text{ (S/m) at 20}^\circ \text{C}$). I am interested in the entry for Carbon (graphite)...
29
votes
2answers
27k views

What is the pKa of the hydronium, or oxonium, ion (H3O+)?

Although the wikipedia page on Hydronium indicates a $\mathrm{p}K_\text{a}$ of −1.74, I noticed in the discussion of this page that the subject seems debated (cf. http://en.wikipedia.org/wiki/Talk:...
28
votes
5answers
60k views

Acid Accident Treatment

What are the general ways to treat an accident involving highly concentrated or similarly dangerous acids? I have a lab instructor who recently debated with our group about treating an acid spill on ...
28
votes
3answers
12k views

Why isn't the American nickel magnetic?

I never thought that modern American nickels actually contained nickel anymore. However, according to this wiki article, the coins actually do contain 25% nickel, the rest being copper. And yet, no US ...
28
votes
5answers
16k views

Why is water "the universal" solvent?

This is an old question that our textbook tried to answer but worsened the situation. Many things are soluble in water. So many, that studying solutions will always require studying aqueous ones. It ...
28
votes
4answers
24k views

Carbon with 5 bonds?

I've heard that, even though according to Molecular Orbital Theory there is no chance of having nobel gases bonded to each other, it is not totally impossible. For example, under extreme conditions, ...
28
votes
3answers
6k views

What properties of carbon dioxide make it a greenhouse gas?

Why is it that heat from the Earth reflects back off carbon dioxide and other greenhouse gases but not gases like nitrogen or oxygen?
28
votes
2answers
7k views

When a candle burns, why does the top of wick glow if bottom of flame is hottest?

Totally an elementary question. Staring at a candle, it appears that the bottom of the wick is dark whereas the top glows. However the bottom of the flame (the blue) is the hottest. Is the reason ...

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