Saponification, or Why Not to Buy The Discount Lutefisk

Soap is ubiquitous in modern life, in many forms, from hand soap to laundry detergent to shampoo. Chemically, soaps are alkali salts of fatty acids, and are formed by taking a fat or oil and combining it, either at room temperature or at or around the boiling point of the fat, with a strong alkali compound like sodium hydroxide. (Alkali compoounds are chemicals that have a high pH; please see the post on the pH scale for reference.) The alkali compound used is usually a hydroxide, either sodium, potassium, or occasionally lithium. All these hydroxides are very reactive, which is useful for forming soap, but they are also very corrosive, and so soapmaking must be done very carefully to avoid accidents.

A typical chemical reaction to create soap

A triglyceride is a fatty acid with three branches. It reacts with NaOH to produce soap molecules with a hydrophobic tail and a hydrophilic head and a molecule of glycerol.

At the heart of soap’s effectiveness is that soap molecules have two distinct parts. One part is hydrophobic (ie, does not mix will with water) and grabs on to dirt (which typically is oil based, ie, also hydrophobic) while the other part is hydrophilic (ie, mixes well with water).

A bit of dirt gets covered in soap molecules, all with the hydrophobic end attached to the dirt, with the hydrophilic end trailing like a string away from the dirt. This structure is sometimes called a micelle, though the term is not just used for soap.

A micelle is formed when soap molecules surround a bit of dirt.

Lutefisk is made in a similar manner to soap, and it’s one of those things, like soy sauce, that I wonder how on earth someone figured out how to make it (and thought to try eating it). It’s a Nordic dish made by taking salted fish like cod, treating it with lye (ie, a very strong alkaline compound) for a couple of days, and then soaking it in water for several days to rinse out the caustic lye. Traditionally, the fish is treated with ash, which is alkaline but not nearly as strong as lye, and then buried for several months. Either way, the chemical reaction between the fats and oil in the fish and the lye needs to be stopped before all the fats saponify; though the whole point of making lutefisk is that some of the fats saponify, rendering the entire fish soap seems even more unsavory than only a partial rendering. The end result is a fish concoction that is somewhat gelatinous and falls apart easily, is either baked or broiled, and looks about as appetizing as you’d expect given how it’s made. I’ve never eaten it myself, but it’s got a reputation for smelling and tasting awful with a very unpleasant texture, but apparently some people genuinely enjoy it. While on description alone I can’t say as I’d recommend it, if you’re going to eat it, it seems especially prudent, given the chemistry involved in making it, to avoid the dented can on the discount shelf at the grocery store.

The pH Scale

There’s a common line in soap commericals that goes something along the lines of “This soap is pH balanced, for soft, smooth skin.” The claim about the soft, smooth skin may or may not be accurate, but what does “pH balanced” mean?

The pH scale is a measurement of the acidity of an aqueous (ie, water-based) liquid compound. The capital H indicates that it’s a measurement of hydrogen ions (denoted H+ in chemical notation); the definitive meaning of the p is lost to the sands of time. A low pH value means that the solution is acidic, and has more H+ ions than OH- ions, while a high pH means the solution is basic (or alkaline — the two terms are interchangeable) and has more OH- ions than H+. The more extreme the inbalance (ie, the lower or higher the pH) the stronger the solution, and the more likely it is to eat through your skin if you spill it.

A flask and a beaker with and acid and basic fluid respectively.

The fluid in the flask on the left is more acidic than the fluid in the beaker on the right is basic.

The precise value of the pH of a solution is given by the negative logarithm of the concentration of hydrogen ions in the solution, though there are compounds that can act as catalysts in specific solutions that will alter the measured pH. Logarithms are a useful way of describing quantities that vary of a wide range of scales. Mathematically, if x = b^y, y = log_b (x).

Logarithmic equations.

Logarithms are typically either in base 10 (ie, b=10) or base e (ie, b = e = 2.718…; these are also called natural logarithms). The most commonly known logarithmic scale is the Richter scale, which measures the strength of earthquakes. The Richter scale is a base 10 scale, so an earthquake of magnitude 6.0 is 10 times stronger than an earthquake of magnitude 5.0, and 1000 times (ie, 10^3 times) stronger than an earthquake of magnitude 3.0.

Similarly, the pH scale is a base 10 logarithmic scale. A solution of pH 4.0 is ten times more acidic than a solution of pH 5.0, and 10 times less acidic (ie, more alkaline) than a solution of pH 3.0. The scale runs from 0.0 to 14.0, (explain why zero can be reached due to catalytic reactions and whatnot)

pH scale

Click to enlarge.

The pH of a solution can be tested using a variety of compounds called indicators that are known to change colour at specific pH values. Indicators do not generally interact with the solution, and so do not drastically alter the chemical mix in the solution. An indicator can be added to a solution, and then the solution can be titrated (ie, another solution is dripped slowly into the original solution to reach a desired pH) until the indicator changes colour. The colour change of the indicator indicates that the solution has reached a specific pH. Litmus paper is a crude indicator: it will indicate if a solution is acidic or basic, but does not determine exactly how acidic or basic the solution is.

In a general sense, then pH balanced, means that the solution in question has the same pH as its surroundings. Skin has a pH of around 5.5, so in the context of facial soap, the manufacturer may be using “pH balanced” to mean that the soap has a pH around 5.5, so the soap will not undergo an acid-base reaction with (and thus irritate) the user’s skin.

Electric Fields

In the last post, I glossed over the bit about how lightning has a hard time passing through air, so I thought I’d clarify (and hopefully this’ll be clear enough that I don’t need to keep up with this string of addenda and clarifications and can write about something new).

From the last post:

The net difference in electrical potential builds up, until the neutral air and water vapour in between the positive and negative regions can no longer sustain the difference, and a lightning bolt discharges the electrical energy. Air is a very good electrical insulator (ie, it is difficult for an electrical current to pass through the air), so a very large electric field can be sustained in the cloud before a lightning bolt discharges the stored energy, and returns at least part of the cloud to a neutral electrical state.

So what exactly is an electric field? It’s a region where, if a charged particle is placed, it will experience an electric force. It’s just like a magentic field: when a magnet (for example, a compass) is placed in a magnetic field (like the Earth’s planetary magnetic field), it experiences a force that aligns it (ie, the compass needle) in a particular way. Similarly, a charged dropped into an electric field will experience a force that pushes it in the field. Electric fields are created by a distribution of charges, either discrete or continuous:

A point charge and a lump of continuous charge, both with electric field lines.

The green lines represent the electrical field.

Of course, the force experienced by a charge dropped into a field depends on the sign (positive or negative) of the charge. A negative charge will experience the opposite force that a positive force experiences, ie, the arrow heads all point in the other direction.

With lightning, it’s not a point test charge dropped into the cloud that creates the bolt, but rather that the charge distribution itself cannot be sustained any longer, and a bolt transfers charge from one region of the cloud to another and neutralizes the field.

Heavily charged cloud with two lightning bolts.

The bolt travels through air, and air is not a vacuum, so the physical properties of the air (or any material that charge is attempting to move through) will affect how easily the charge can move through the material. Materials (and by materials I mean any state of matter, so it can include say glass, water, and air) can generally be classified as either insulators or conductors, depending on a property called conductivity. Electrical energy has a hard time travelling through insulators (like glass) which have a low conductivity, while it passes easily through conductors (like metals), which have high conductivity.

The electrical conductance (or resistance, depending on how you look at it) depends on the atomic or molecular structure of the material. Metals are excellent conductors of electricity, due to their atomic structure. Metals, by definition, have a lattice structure, with loose electrons that can propagate throughout the metal and are not confined to a single atom.

Schematic of metal lattice of positive ions, with an electron that is free to propagate through the lattice.

A very small piece of a metal lattice. The positive ions (nuclei) form the lattice, and the negative ions (valence electrons) can propagate throughout the lattice.

These loose electrons, which are negatively charged, carry electrical charge throughout the material. When a charge is applied at one end of a piece of metal, that charge quickly and efficiently propagates throughout the metal, as the loose electrons move throughout the metal in response to the introduced charge.

But not all materials are metals, and many do not have such loose electrons to acts as charge carriers. Glass, for example, is an excellent insulator, because it has an amorphous, non-crystalline molecular structure. There are no loose electrons, and so few loose charge carriers, and an applied electrical charge has difficulty propagating through the material.

A schematic of glass's crystal structure.

Glass does not have a regular lattice structure, so electrons do not propagate easily through it.

Air is like glass, in that even though there is plenty of room for particles to move freely, there are very few charge carriers to transfer electrical energy from one location to another. This means that a very large electric field can be sustained across a cloud, as small amounts of charge have a hard time flowing freely between the two regions. There is no such thing as a perfect insulator, and eventually the air cannot sustain the electric field, but since it is such a good insulator, the bolt that discharges the energy is very energetic, which we see as a bright flash and hear as a clap of thunder.

Lightning and Thunder

While the last post talked about how thunderstorms form, it didn’t discuss either thunder or lightning (it was getting a bit long). So let’s talk about that!

Lightning is a discharge of electrical energy between different regions within a thundercloud, and it’s a byproduct of a thunderstorm, not a critical element to the storm’s formation. What is critical is the updraft that pushes lots of moisture into the atmosphere where it condenses and forms a thundercloud, and it’s this updraft that is thought to be what drives the electrical structure of a thunderstorm as well. (The precise mechanism is not totally understood.) The updraft forces the circulation of particles within the cloud. As ice and water particles collide within the cloud, they form and break apart. Small ice particles tend to gain a net positive charge, and the larger slushy particles tend to acquire a negative charge. The (positively charged) ice particles are smaller and are more easily pushed to the top of the cloud by the updraft, while the negatively charged slush particles particles fall to the middle and bottom of the cloud. The Earth also acquires a net positive charge in the area underneath the storm, as the concentration of negative charge at the bottom of the cloud induces a positive charge directly below it.

Thundercloud with positive charge at the top and negative charge at the bottom.  The ground below has a positive charge too.

The red arrow is the updraft that drives the circulation within the cloud.

The net difference in electrical potential builds up, until the neutral air and water vapour in between the positive and negative regions can no longer sustain the difference, and a lightning bolt discharges the electrical energy. Air is a very good electrical insulator (ie, it is difficult for an electrical current to pass through the air), so a very large electric field can be sustained in the cloud before a lightning bolt discharges the stored energy, and returns at least part of the cloud to a neutral electrical state.

Heavily charged cloud with two lightning bolts. Thundercloud with regions now neutralized after lightning bolt.

What appears as a single, instant bolt of lightning is usually made of several bolts of lightning that occur so quickly that the human eye perceives them as one. An initial “leader” bolt, which is not very luminous, extends down from the cloud to the ground. In response to the charge, tall objects form “streamers,” which are strands of positive charge that extend up towards the negatively charged leader. The leader often branches several times, and if one of those branches connects with a streamer, negative charge flows from the cloud to the ground. Nearly instantaneously, positive charge flows from the ground to the cloud along the path formed by the leader. This is the extremely bright that we see; the charges can zip back and forth between the cloud several times in what we see as a single bolt.

Branched lightning meeting streamers from a tree and a house.

The yellow leader may branch several times; the blue lines from the tree and house are streamers.

Most lightning occurs within a cloud (or between two different clouds), but lightning between the (usually negatively charged) bottom of the cloud and the (usually positively charged) Earth is both better understood and much more distructive. Most lightning that occurs between a cloud and the Earth occurs between the bottom of the cloud and the earth, rather than the top. However, some lightning can form from the top of the cloud, arcing all the way to the ground. When that happens, the charge from the cloud is positive and the induced charge from the ground is negative (ie, the opposite of lightning that forms from the base of the cloud).

Lightning bolt from the top of the cloud to the ground.

Thunder accompanies lightning, because as the lightning bolt extremely suddenly heats the air around it, the air is compressed into a shock wave. The compression shock is very localised, since lightning is extremely hot (~20,000 degrees Celsius) and extremely shortlived (~30 microseconds), and the shock decays into an acoustic wave, which we hear as a clap of thunder. Since sound travels much more slowly than light, the time between when you see a stroke of lightning and hear the accompanying clap of thunder can be used to estimate how far away the lightning bolt was. A difference of 5 seconds means the bolt was around a mile away, and a difference of 3 seconds means it was about a kilometer away.

How Thunderstorms Form

It’s the middle of winter here now, so let’s start off with something that happens much more in the summer here.

All thunderstorms need a few ingredients to form, including a source of moisture, warm wet air and cold dry air that interact, and a mechanism to trigger an updraft (more on this in a moment). In North America, the source of moisture is often either the Atlantic or Pacific Ocean, or the Gulf of Mexico — the moisture does not need to be where the thunderstorm forms, but rather where the air that feeds into the thunderstorm originates from.

Air flow over North America.  Cold dry air comes from the west over the Rockies, while warm wet air flows up from the Gulf of Mexico over the middle of the continent.

Warm air blows over (say) the Gulf of Mexico, picks up moisture, and then continues on into the Southern US, where it may form a thunderstorm. This warm, wet air is typically close to the planet’s surface — it picks up the water from the ocean, and does not rise very high (yet). This low, warm, wet air may encounter cold, dry air from the Rockies. If this happens, the warm wet air will be lifted up by the cold air, and the moisture in the air will condense into a cloud.

Lifting mechanism.  Cold air is denser than warm air, so when warm and cold air meet, the warm air is lifted upwards.  The moisture in the warm air condenses into a cloud.

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Welcome to Eight Crayon Science!

One time a couple of years ago, when I was working on my MSc, my parents took me out for dinner, and in the middle of it, my Dad handed me a pocket notebook and a package of eight Crayola crayons and asked me to explain my thesis to him.  I found a blank page, thought for a minute, and tried to put my very abstract thesis into pictures, to moderate success — art is not something I’m talented at, and the pictures ended up squished in a corner of the crowded page.  It must’ve made an impression on my Dad, though, because since then, whenever my Dad has asked about what I’m working on, he’s made a quip about having a package of crayons waiting for me.   

My parents are both very smart people, but neither of them have much of a formal background in science beyond high school.  Science is often communicated in technical language, which is often very discipline-specific and can be very obscure, or through popular media, which frequently obscures or misrepresents the findings.  However, I believe that having a grasp of solid, evidence based science is becoming increasingly important, regardless of what level or kind of formal education a person has.  This blog is my attempt to lay a plank over the gap between the technical language of science and the lay language of people like my parents.  Eight Crayon Science is not about jargon, obscure details, or pages of formulas and mathematics. It’s about the fundamental ideas underpinning the science that affects our everyday lives. It’s about communicating those ideas, discoveries, and theories in a way that’s clear, honest, and hopefully accessible. It’s about fostering a dialogue about science that everyone, not just specialists and scientists, can participate in comfortably — and I hope you do! Science is helping to provide us with the means to understand some of the most important changes occurring in the world around us, and I hope you’ll join me in exploring and discovering our world.

If you have any questions, comments, suggestions for posts, or feedback, I would love to hear from you. Please email me at eight.crayon.science {at} gmail {dot} com. Welcome aboard!