52

As Nilay Ghosh said, nitrogen is cheap. Very cheap. Neon is expensive. Argon is cheaper than neon, but considerably more expensive than nitrogen. Helium is also expensive and needs to be used wisely, for important things, e.g., cryogenics. And hydrogen! I can just see the ads: “Buy our chips: they are lighter than air! But avoid open flames and sparks unless ...


44

Not mentioned yet: nitrogen is entirely non-toxic, environmentally friendly, does not contribute to global warming or ozone depletion. In very good approximation, nitrogen is just air with the oxygen removed that would oxidize the contents. The usual production process consists of liquefying air, distilling it, and then selling the gases separately. This ...


27

Substances that are gaseous down to, say, -10 are finite (and not very large) number. Of these, we want: Safe against ignition (so no hydrogen or gaseous hydrocarbons) Not poisonous (phosphine, arsine, carbon monoxide - out!) Not corrosive (chlorine, fluorine - sorry) Without unpleasant smell (hydrogen sulfide is no-go) Not related to processes of food ...


24

Measure the change in mass over time of the remaining liquid. Though some water will also evaporate, you can control for that by keeping the humidity near 100%. If you have to be precise, collect the outgassed $\ce{CO2}$ in a liquid-nitrogen cold trap. Check the mass of the condensate, which should equal that lost from the soda. Check purity, to be really ...


23

The answer to this question lies in the pharmacokinetics of these two drugs: the acetyl groups cause Heroin to be 200 times more lipid soluble than Morphine1. Another example of a common drug would be Fentanyl, which is 580 times more lipid soluble than morphine, with a structure very similar to that of Morphine. Increased lipid solubility allows these drugs ...


22

They're not exact numbers. These numbers aren't exact for three reasons: Each type of carb, protein, and fat has a different caloric value. These are overall averages for each class. Even if you were dealing with a single pure compound, the value couldn't be exact because there is individual variation in how much of that compound is metabolized based on ...


17

Avoiding cooling again after keeping it ( for non critical products ) at room temperature is mainly to prevent forgetting it was not cold all the time and that it may will not last as long as expected. Taking food from the fridge, you may not remember after a week or two that it was outside longer than it should be. It can violate the safety by growth of ...


16

When looking at IR spectra of hydrogen-bonding groups, always check how IR spectra was recorded. It appears that NIST spectra is recorded using gas phase, while the first one used liquid film. In liquid film $\ce{NH2}$ groups form a network of hydrogen bonds, resulting in shape distortion and widening of $\ce{NH2}$-related bands. Same is true for carboxylic ...


14

The numbers in the code have nothing to do with viscosity index. However, your understanding of 'W' for winter is correct. The real code for your car is actually SAE 5W-30 where SAE stands for the Society of Automotive Engineers, which has established a multi-grade numerical code system for grading motor oils according to their viscosity characteristics. I ...


13

Measure concentration in a fixed volume of air Easiest way might be to put it in a sealed impermeable bag or box and measure the CO2 concentration over time. Home hobbyists use something like the MG-811 CO2 sensor or a simple non-dispersive optical sensor and connect it to a Raspberry Pi or Arduino using an analog to digital converter chip (ADC). For (a ...


12

Answer here from a quality manager in the pharmaceutical field in Europe. Pharmaceutical companies are obliged to perform stability tests for their products according to the relevant pharmaceutical (GMP) agency in your market (FDA/EMA/etc) and the international agreed guidelines like ICH Q1A-F and the WHO). These tests are carried out in stability chambers ...


9

Yes, 9.5% is much to high a value. Let's break the problem into two parts. $p_\mathrm{C}$ will be the probability of getting exactly one $\ce{^{13}C}$ atom in a molecule with 12 carbon atoms. $p_\mathrm{N}$ will be the probability of getting exactly one $\ce{^{15}N}$ atom in a molecule with 2 nitrogen atoms. $p$, the probability sought will be $p = p_\...


9

I recommend the @Stanley Yu own answer, as I admit I was not particular familiar with the shape of the ON number curve. It is done by an extrapolation of the critical compression ratios of mixtures 0-100% of isooctane and 100-0% of n-heptane for ON values <0 and >100. If, just illustratively, 100% isooctane had the critical compression ratio 1:20, 90% ...


9

It doesn't "take one calorie to burn", you gain one calorie by burning. Now noting obviously what everybody else has said about selection of the type of fat affecting the precise amount of energy available from one gram (which in practice will be measured in a calorimeter), but what this is really saying is that by metabolising some specified ...


7

To start, we must first understand that we can ignore the counterions to the $\ce{Ca(ClO)2}$ and the $\ce{NaClO}$. Typical household bleach claims to have a concentration of 6% (w/v). Now we can do some basic arithmetic to convert the percent weight by volume of sodium hypochlorite in water to a molar concentration: $\mathrm{\frac{0.06\,g}{1\,mL}}$$\mathrm{\...


6

For a direct measurement of $\ce{CO2}$ content, it is possible to use infrared (IR) spectroscopy. Infrared radiation can be absorbed by molecules, causing them to vibrate. The exact frequency of the radiation absorbed is often characteristic of certain bonds or functional groups. In particular, the fundamental antisymmetric stretching mode of $\ce{CO2}$ in ...


6

Tetracarbon pentoxide, $\ce{C4O5}$, does not appear to be known, but Wikipedia reports what has become a surprisingly large variety of oxocarbons. They include simple carbon monoxide and carbon dioxide, various extended linear structures, single and multiple rings, oligomers and polymers, even fullerene oxides. Some are surprisingly stable: mellitic ...


6

$\ce{C4O5}$ can be found in a Chinese patent art(Ref. 1). It is called Oxolane-2,3,4,5-tetrone both in the patent and PubChem. In the patent, $\ce{C4O5}$ is shown as compound 2 and appears to be a compound which undergoes further reaction with itself eventually giving a desired product. A google translation of the relative portion of the patent, from ...


6

Honestly I have doubt about your textbook version of IR spectrum. However, I can suggest by the experience I have gained that the shapes of the peaks depends on the method you have used to obtain the spectra such as ATR, smear, absorbed in inert surface, etc., thus cannot pinpoint which one is incorrect. Yet, you can compare an one with other related amines. ...


5

This has everything to do with heat conduction, Setting aside freezing or melting for the time being, the two things that are happening in combination are (1) heat conduction and (2) the capacity of a parcel of solid to store thermal energy by its temperature changing. Heat conduction is driven by a spatial gradient in temperature, with heat flowing from a ...


5

According to Scott and Jones1: ... problems arise with branched alkyl chains, a side chain methyl group or a gem-dimethyl-branched chain cannot undergo β-oxidation by microorganisms and must be degraded by loss of one carbon atom at a time (α-oxidation). * text by the authors, highlighting and hyperlinking by me. A study by Whyte et al2 on the degradation ...


5

The single measured values provided by 3 different tools gives us just a hint about possible accuracy or precision of the tools. The tool providing the value 1.39 is probably, but not necessarily more precise and accurate than the other two. What these values really say is just the tool resolution. There are 4 terms: resolution precision accuracy(1), also ...


4

Mole itself doesn't have a magnitude, but the value of mole does, in fact it is the magnitude. Any measurement has a magnitude (ie for the mass of 5 kg the magnitude will also be 5). I think you are confusing it with scalar measurements (ie forces) which also have a direction. For example 5 Newtons 'in that direction'. Mole is similar to a dozen (just a ...


4

You don't have problem with assigning compound IV (1, 4, 5, 6- tetrahydropyrimidine) as the most basic compound among given four amines. I agree with you, but not the same reasons. According to Ref.1, the 1,4,5,6-tetrahydropyrimidines (THPs) are extremely basic compounds, as might be expected from their amidine structure (e.g., 1,8-Diazabicyclo[5.4.0]undec-7-...


4

There are two types of erasable pens: rubber cement and thermochromic pens. Thermochromic pens are much more popular nowadays because rubber cement pens literally harden like cement, and can't be erased after a few hours. Thermochromic pens, however, use heat from friction that makes the ink invisible; not exactly removing it from the paper, but close enough....


4

You might want to use a $\ce{CO2}$ ion selective electrode, such as PS-3517 from PASCO: This Carbon Dioxide Ion Selective Electrode (ISE) Probe is a gas-sensing electrode that allows fast, simple, eco-nomical, and accurate measurement of dissolved CO2 in aqueous solutions The advantage over other methods is that you measure the concentration in situ and ...


4

It depends if the substance in bulk is transparent, highly reflective (metallic) or highly absorptive. Carbon in its graphite allotrope is highly absorptive, and even finely divided is still black. Carbon as diamond is transparent. Crushed diamonds are white -- look at a diamond file or abrasive disk. What happens is that incident light is scattered as it ...


4

UVC is very harmful to people and requires specialist equipment to create and use safely You are not going to be able to create or use lamps that emit 222nM light without specialist equipment, and even if you could it would almost certainly not be safe. Far UV lamps are widely commercially available for germicidal applications and these usually use mercury ...


4

Question: What is the practical significance of the shape of conical flask (in US: Erlenmeyer flask)? An Erlenmeyer flask (also known as a conical flask or a titration flask) is a type of laboratory flask, which consists of a flat bottom, a conical body, and a cylindrical neck. The flask is created by the German chemist, Richard August Carl Emil Erlenmeyer (...


4

According to the standards group ASTM International, octane numbers above 100 are defined using the formula: $$ON=100+\frac{28.28T}{1.0 + 0.736T + (1.0 + 1.472T - 0.035216T^2)^{0.5}}$$ where $T$ is "mL tetraethyllead (TEL) per U.S. gal in isooctane" [1]. This is the standard used by the FTC to regulate automotive fuel ratings in the US [2]. It should be ...


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