White Lines; Acid Queen

This is going to be serious and focussed, because it's supposed to provide educational materials.

Here are today's two videos:

Introduction to the chemistry of acids, bases and salts. Click to tweet:  http://clicktotweet.com/e3Xab .

Acids are, according to some definitions, substances which produce hydrogen ions in solution.  Bases, or rather alkalis, are substances which produce hydroxyl ions in the same circumstances.  This is an inaccurate and sketchy definition, but it's the one used at GCSE and IGCSE so for the sake of that i'll stick to it for now.  Some compounds do both.  These are referred to as amphoteric.

Acidity and alkalinity are measured on the pH scale.  This indicates how many hydrogen ions are present in solution on a scale which changes tenfold with each step - a logarithmic scale (multiplies rather than adds).  Acids are low - below 7 - whereas bases are high - above 7.  Neutral is at 7 itself.

When an acid and a base react together, the process is referred to as neutralisation and the compound which results is called a salt.  Although table salt is a salt (for instance of hydrochloric acid and caustic soda), any such compound is also a salt.  The salt i make in this video, which is inaccurately measured for reasons which will be explained in Part II, is citric acid combined with sodium hydrogen carbonate, or sodium citrate.  This combination also indicates the test for carbonates, which tend to release carbon dioxide when combined with acids.

Please watch part II as well, which is here:

Acids And Bases Part II of II.  Click to tweet:  http://clicktotweet.com/03fFk .

Please watch this in conjunction with Part I as it follows on from that.  This is how to make indicator solution using red cabbage water, which works because of the anthocyanins.  I also go through some of the properties of acids and bases.  Bases are bitter and have a soapy feel to them because of saponification of the oil in your hands when you handle them, which brings up a whole philosophical issue but let's leave that for now.  Acids are sour, release hydrogen with metals and form metal salts from metal oxides.  The indicator i made goes red with acid, green with alkali.

Then i go on and on about how rubbish GCSEs are, which is probably not very helpful.  Sorry about that.

I've missed out a few things, which i'll cover here.  

Firstly, though i might've said this already, metals in stronger acids liberate hydrogen and replace the hydrogen itself in the acid, so for example sulphuric acid and copper form anhydrous copper sulphate and liberate hydrogen.  However, this doesn't happen in weaker acids.

Secondly, anthocyanin is not the only indicator and some respond better than it does at other pH levels.  One example is methyl orange:

which looks like this:

and is yellow in alkali and red in acid.  Another one is litmus, which is mainly 7-hydroxyphenoxazone, from the lichen Roccella tinctoria (note the species name), and some others.  Lichen is also used to dye tartans, such as ours:

and:

Clearly i'm not that keen on litmus because lichen grows quite slowly.  Litmus turns blue with alkalis and red with acid.  There are a number of others, including phenolphthalein, a laxative which turns fuchsia with bases and orange or colourless (depending on the type) in acid.

Thirdly, here's something i've not emphasised enough, probably:  acids are acids, but bases are not necessarily alkalis.  In order to be an alkali, bases must dissolve in water.  Copper oxide is a base but not alkaline, for example.

Fourthly, i've said "hydroxyl" all the way through these videos when i should've said "hydroxide".  Sorry about that.

Fifthly, salts can be considered to be related to each other in families connected to their acids.  Sulphates are connected to sulphuric acid, nitrates to nitric acid and chlorides to hydrochloric acid.

That's it for the GCSE subject matter, but it's now got to the stage where this is really bugging me, so i'm going to scratch that itch now!

The problems with this:

• The definition of an acid.
• The assumption that all this is happening in water.
• The idea that there are "hydrogen ions", i.e. actual free protons wandering about in water.

Let's start with the last thing first.  What actually happens is that "hydronium ions" form with acids in water, not hydrogen ions.  These are H3O (best i can do on here i think) ions - that's also inaccurate because protons associate with several water molecules at once.

Penultimately, water is not the only solvent.  Another example, oft-quoted, is ammonia, and since ammonia is itself a base, neutral pH in it is in a different place, which means that all acids are strong acids in it and there are relatively few alkalis with respect to it.  This may have consequences for the probability of extraterrestrial life, because it means that the nucleic and amino acids so important for life on this planet would all be strong acids in liquid ammonia.

Antepenultimately, and related to the previous point, acids can be defined in various ways.  The Bronsted-Lowry theory defines acids as proton donors and bases as proton acceptors.  This makes no difference to water but also enables the idea of acids and bases to be extended to other solvents than water, such as ammonia, sulphuric acid and glacial acetic acid (which is pure acetic acid - nasty stuff).  However, for that very reason, the Bronsted-Lowry theory fails to allow a more absolute definition of acid or base - they all depend on the solvent they're in.

One answer to this is the rather extreme version of the definition in which acids accept electron pairs and bases donate them.  This makes almost all chemical reactions acid-base reactions, which is weird and makes the whole notion meaningless.  This is known as the Lewis Acid theory.  An even broader definition is that and acid is anything which reacts with bases, gives up cations or accepts anions or electrons, which includes redox reactions.

Then there is Lux-Flood, which i can't understand right now as it says acids are oxides which accept oxygen and bases are oxides which donate oxygen, and i can't see how this applies to hydrochloric acid, except that hydrochloric acid is actually a gas called hydrogen chloride which dissolves in water to become acid, so maybe that's it.

There's also something called the solvent system.  It's probably the best but i haven't a clue what it is.

Phew!  That's better.

I'm now torn between doing something about urinalysis or something about how much GCSEs bug me because of the dumbing down.

Blue soda bread and home science

One of the brilliant things you can do at home, which is also really colourful, is make your own pH indicator from red cabbage water.  Here's a particular use for it which occurred to me the other day:

Making naturally blue soda bread.

The way this works is that so-called "red" cabbage (which i think of as purple) is very high in an anthocyanin.  The word "anthocyanin" is from the Greek words anthos -  flower, and kyanos - blue.  Anthocyanins are in fact not necessarily blue but all sorts of colours.  They are also useful in herbal medicine.  For instance, the skins of Sambucus nigra (elder) berries are high in anthocyanins which soothe the throat and are useful in coughs and sore throats.  They are almost entirely tasteless and occur in a wide range of flowering plants with the exception of the Caryophyllales, a large order containing such plants as beetroot and cacti, which instead contain betalains.  These two types of compound are never found in the same species.

Anthocyanins are derived from other compounds called anthocyanidins, whose molecular structure can be drawn like this:

The red numbers show where variations occur in the structure.

The substances occur in petals, leaves and some other parts of the plant, in vacuoles, which are "bubbles" of unorganised liquid surrounded by membrane inside the cells.  The acidity or alkalinity of the liquid determines the colour.  They are also responsible for the colour of some fruit, such as the redness of ripe apples.  They may also stop animals which are attracted to green plant parts, which they then eat, from consuming flower petals, and they also attract pollinating insects to flowers.  Their precise shade of purple is complementary to the green of leaves, so they don't block any light which the plant could use for photosynthesis.  This also means that the older photosynthetic organisms with which the plants had to complete billions of years ago would have been exactly that shade of purple too, so if we ever get to another planet where that quirk in the history of life didn't happen, we'd be quite likely to find that the plants were all the colour of anthocyanins, though only if the star the planet orbited was the same colour as the Sun.

Elderberries

Another aspect of anthocyanins is that they form the purple dye colour which is the easiest rich colour to use on cloth in natural dyeing.  Cotton, for example, dyed with elderberries is initially such a strong colour that it looks completely artificial.  Unfortunately, it also fades much faster in sunlight, probably for that reason.  They are sadly quite unstable.

As you can see from the video, anthocyanins are also excellent indicators.  They turn red in acid and blue-green in alkali.  In a strong caustic soda solution, about which i will soon make a video, they become orange.  The reaction between the sodium bicarbonate and lime juice, incidentally, produces a sodium citrate, of which there are three different types, and releases carbon dioxide, which occurs when any alkaline carbonate is combined with an acid.  Disodium citrate can be used to reduce the discomfort of cystitis and urethritis, and is one of the approximately twenty compounds which can easily be made at home from common organic acids and alkali and alkali earth metal compounds.  Compounds which are combinations of acids and bases are known as salts, so the sodium citrates are good examples of organic salts.

The other thing about all this is that the soda bread, which to be honest i perceive as pale turquoise rather than green or blue, is an example of a blue food.  Genuinely strong blue foods have long been an obsession of mine because there are so few of them, and the ones which are claimed to be blue or called blue usually aren't, such as blueberries, pasta coloured with squid ink or "blue corn".  However, there are a few foods which are genuinely blue, and this is one of them, though being soda bread it's probably partly antinutritional.  Another food which would be blue for the same reasons if it existed would be the Finnish salmiakki, which is high in sal ammoniac or ammonium chloride, mixed with liquorice:

  Besides that, there are rather few, but they would include cornflower or borage petals and raw bruised Boletus fungi:

Cornflower

Borage - Borago officinalis - i actually use this quite a lot, partly for its fatty acids.  There are pyrrolizidine alkaloids in it though, so i'm not incredibly keen, and it tends to go off very quickly which is also annoying.

Boletus - don't know which species, but they turn distinctively blue on cutting.  Not all are edible though, either

Anyway, i don't seem to share the general aversion to blue food and was only fearful of the blue soda bread because i was expecting it to taste like a combination of cabbage and bicarbonate of soda, but surprisingly it turned out to taste absolutely fine and was really nice.  I think i just got lucky with the quantity of soda though.

Unfortunately, this is the second time i've made something non-vegan for a YouTube video in a week, so i need to make amends in some way.