Hot answers tagged

85

The odour threshold for hydrogen cyanide $(\ce{HCN})$ is in fact quite a bit lower than the lethal toxicity threshold. Data for $\ce{HCN}$ can be found in many places, but here and here are a couple of good references. That subset of the human population that can detect bitter almonds do so at a threshold of $0.58$ to $\pu{5 ppm}$. The lethal exposure dose ...


67

No. There are sweet, bitter, and various other salts. (Likely, there are tasteless salts too). Pure salty taste is as far as I know exclusive for table salt, though I wouldn't bet on it. Lead and Beryllium salts are said to be sweet, though toxic. Epsom salt, $\ce{MgSO4}$, is bitter. $\ce{CuSO4}$ has an incomprehensible, persistent metallic taste. (Based on ...


55

The stains are due to silver nitrate, the reactive portion of Tollens’ reagent. It is very prone to reduction to metallic silver. If you got it on your hands (a clear signal you weren’t wearing gloves when you should have been) it will create small silver particles in your skin — this is why it won’t wash off. Since the particles are small, they don’t ...


50

First I'd locate the bottle which causes the problem. Usually HCl is #1 suspect, but to be sure you can put a vial with smelling salts (aqueous solution of $\ce{(NH4)2CO3}$) or ammonia in the box with acids; white coating of $\ce{NH4Cl}$ on the bottle signifies the leak. It's also a good practice to store acids in glass bottles with a proper joint (teflon ...


42

My Lab First Aid book$^{*1}$ tells the following: The local therapy mainly consists of the instant, intense rinsing (at least 10 minutes) with tap water (ideally 15 to 20 °C). Don't try to neutralize the chemical burn, because the heat generation could lead to further tissue damages. This means, that your lab instructor is absolutely right. The rinsing ...


37

It is known that ammonium nitrate decompose exothermically when heated to form nitrous oxide and water. This paper1 notes that the irreversible decomposition of ammonium nitrate occurs at the temperature range of $\pu{230-260 ^\circ C}$. $$\ce{NH4NO3 ->[t >230 ^\circ C] N2O + 2H2O}$$ They also further noted that beyond $\pu{280 ^\circ C}$, $\ce{NH4NO3}$...


36

Saltiness is perceived when alkali metal enter taste buds. From wikipedia: Saltiness is a taste produced primarily by the presence of sodium ions. Other ions of the alkali metals group also taste salty, but the further from sodium the less salty the sensation is. The size of lithium and potassium ions most closely resemble those of sodium and ...


35

Recognize that a whiff of most toxins, even in high concentration, will probably not kill you. You need a sufficient concentration in your blood - which means you have to actually get a certain number of HCN molecules to penetrate across the mucosa of the lung and into the blood stream. Typical breathing volume is about 500 mL (tidal volume), about 1/40th of ...


35

First, why other options are not really the options: A: vinegar, being a weak acid, doesn't neutralize sulfuric acid and only dilutes it; B: solid sodium hydroxide, a strong base, does neutralize sulfuric acid, but it does so vigorously releasing substantial amount of heat per unit of time: $$\ce{2 NaOH(s) + H2SO4(aq) -> Na2SO4(aq) + 2 H2O(l)}$$ Using ...


32

A fire has no way to directly "draw in" oxygen for it to burn. It consumes what oxygen is in the immediate vicinity of the flame, depleting the air in oxygen compared to the concentration of oxygen in air further away. This sets up a concentration gradient such that oxygen will diffuse into the depleted region near the fire. An even more important process ...


31

I think the use of Hydrofluoric Acid was script-driven rather than fact driven: it sounds scary rather than being a good choice. Also, it allows for the possibility of the darkly comic bathtub scene where the acid dissolves a ceramic bath because Jessie ignores Walter's instructions (which establishes Walter's expertise and Jessie's lack of it). There is no ...


30

This is more a comment than an answer, but too long for the former.... There are two things for you (and your company) to consider: The SDS of the chemicals being handled - that will give you guidance for how best to handle a chemical. Flavouring chemicals like benzaldehyde, cinnamaldehyde, limonene all have irritation warnings, and need to be handled in ...


29

Summary: there is not necessarily a contradiction between the two. Radiation is not contagious, and a person who has been exposed to ionizing radiation is not dangerous to other people once they are not contaminated with radioactive material any more, but while they are still contaminated with radioactive material, they may pose a danger (highest danger is ...


28

Ammonium nitrate ($\ce{NH4NO3}$) is widely used in the fertilizer industry and is one of the most concentrated forms of nitrogen fertilizer (35% of $\ce{N}$). At the same time, it has also been widely used as an explosive material for detonation in mines. Because of its explosiveness, $\ce{NH4NO3}$ is associated with various hazards including fire and ...


27

If you spill nitric acid onto the table, you yourself are unharmed and you can use a cool head to decide what to do next. If the spill is small, pour water on it to both dilute it and dilute the heat — remember water has a high specific heat capacity. If the spill is larger, I would probably try adding sodium hydrogencarbonate to react away the acid before ...


26

A lab coat will eventually get dirty, that's why it is a good idea to wear it. I had a lot of students complaining about the condition of their coat and they asked me if they could just wash it in the washing machine. My answer was always no. As far as I remember - I am a theoretician now - a labcoat costs much less than a pair of trousers and a T-shirt. ...


26

The visible fog that forms when liquid nitrogen is poured into an open container is almost entirely water fog: the boiling nitrogen chills the air above it, causing the humidity in the air to condense into fog. There may be some microdroplets of liquid nitrogen in the fog too, but the air, even after it's been chilled, is still much warmer than the boiling ...


26

Collecting together the responses from the comments and Ben Norris's answer and adding one of my own, individual solutions in water of the following chemicals are realistic options for a liquid spill in a high school chemistry lab, leading to destroyed clothes and time under a safety shower: Potassium permanganate $(\ce{KMnO4})$ Sulfuric acid $(\ce{H2SO4})$ ...


22

If you don't mind, I'll start with a more colloquial and hopfully not to lengthy explanation: Precious metals, such gold, do not corrode under "household conditions", others, such as iron or aluminium do. Rusting of iron is a typical example. Here, the corroded surface often is very porous and the corrosion carries on until the whole piece of metal is ...


18

First, let me say that I've enjoyed many times exploding soap bubbles of about one milliliter filled with hydrolysis gas. That is 1 cubic centimeter. That will give you a sound that rings in your ears in a decent sized living room. You may wish to use ear protection for the experiment. 50 ml will have an effect in a lecture hall that not only wakes up ...


18

Gatterman reports (Org. Synth. 1927, 7, 50, as a footnote) that people who smoke regularly have enhanced sensitivity to the smell of cyanide gas, and he recommend smoking while preparing it! Organic Synthesis Collective Volume 1 1941 314-315 Just opening the NaCN container, most regular (and former regular) smokers can smell the trace amount of HCN formed ...


17

Speaking from experience. Minor spills (drops) on skin of concentrated nitric or sulfuric acid are nothing to speak of. Wash them off with plenty of water for a minute or two and you are fine. I'm pretty sure that this is the case for phosphoric acid as well. Hydrochloric acid is a bit more troublesome, mosly because it fumes intensively, but still nothing ...


17

The real high school accidents that I know of involved flammable liquids (ethanol or methanol) igniting. Mishaps in school labs reveal lack of safety (PDF link) Two high school kids burned in lab accident 6 injured in chemistry classroom fire at Woodson High in Fairfax Safety Alert Rainbow Demonstration If you want to be realistic, base on the above....


16

Diborane. NIOSH gives NFPA 4-4-4-W:


16

permeakra is quite right with his counterexamples of salts that don't taste purely salty, but I'd like to expand on why. We haven't fully identified and elucidated the receptors involved in taste, but they can be broadly classed into tastes people are familiar with: salty, sweet, sour, bitter, and umami. Salty and sour receptors are both known to be mostly ...


16

In a lemon battery, the zinc from the galvanized nail is giving up electrons and transitioning into an aqueous state: $$\ce{Zn → Zn^2+ + 2e−}$$ While zinc is entering the electrolyte, two positively charged hydrogen ions ($\ce{H+}$) from the citric acid with two electrons at the copper electrode's surface and form an uncharged hydrogen molecule $\ce{H2}$: ...


15

I'm afraid this answer doesn't address where you can get $\ce{SF6}$, as I don't know any suppliers myself (it would probably help to specify where you are, though). I just want to straighten out the safety details and make sure you (and anyone else who reads this in the future) know what you're doing. All chemistry experiments can take a turn for the worse ...


15

It is protection. It should be worn whenever you work with potentially dangerous chemicals. In German, it is even called (part of the) persönliche Schutzausrüstung, i.e. personal protective gear. Lab coats: protect you against contamination with chemicals — acids, bases, toxic molecules and salts. They will ‘hit’ your coat and ‘stick’ to it rather than ...


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