No Both reactants and both products are soluble in water.

Quality Assurance

When you can solve these problems without consulting the tables, you should be able to predict the outcome of about half the reactions in this book. Your notebook for this project may omit the "Observations" section, as no manipulation of materials is involved in this project. Include any examples you worked in your notebook along with a flawless metathesis quiz. Also include your analysis of the relative toxicities of caffeine, sodium chloride, sucrose, and sodium cyanide.

Chapter 8. Job (Alkali)

Again there was a day when the sons of God came to present themselves before the Lord, and Satan came also among them to present himself to the Lord. And the Lord said unto Satan, From whence comest thou? And Satan answered the Lord, and said, From going to and fro in the earth, and walking up and down in it.

And the Lord said unto Satan, Hast thou considered my servant Job, that there is none like him in the earth, a perfect and an upright man, one that feareth God and escheweth evil? and still he holdeth fast his integrity, although, thou movedst me against him, to destroy him without cause.

And Satan answered the Lord, and said, Skin for skin, yea, all that a man hath he will give for his life. But put forth thine hand now, and touch his bone and his flesh, and he will curse thee to thy face

And the Lord said unto Satan, Behold, he is in thine hand; but save his life. So went Satan forth from the presence of the Lord, and smote Job with sore boils from the sole of his foot unto his crown.

And he took him a potsherd to scrape himself withal; and he sat down among the ashes.

8.1.

You are probably wondering why I am sitting here in the fireplace, covered in ashes, and scraping myself with a piece of broken crockery. I will tell you. First of all, you must know that Satan, having nothing better to do, convinced God to let him take away my oxen, my sheep, and my camels. Not satisfied, he also insisted on knocking down my oldest son's house with all my sons and daughters inside. And now he has given me a rash that itches like the dickens. You must also know that my wife, who urged me to curse God and die, has not so much as a zit. Anyway, I am scratching myself with a broken pot because the itching is unbearable. And to avoid infecting my open, running sores, I cover myself in ashes. These ashes, of course, are rich in potassium carbonate, which hydrolyze the cell walls of any bacteria which may happen to drop by. But I am getting ahead of myself.

I will not, of course, know about either potassium carbonate or bacteria for another six thousand years. But my mother, who was something of a clean freak, taught me all about potash, which comes, of course, from soaking ashes in a pot. "Potash," she would say, "can wash the stink off a Chaldean, the dirt off a Sabean, and the smirk off any son of mine." A strict woman, my mother, but she knew her cleaning supplies. Actually potash was her only cleaning supply. She used it for washing clothes and dishes, for scrubbing furniture and children. And since disease comes from being unclean, she would make us cover ourselves in ashes at the first sign of trouble. It was, for her, Chlorox, Comet, and Bactine all rolled into one.

Notes

8.2.

If you would like to understand potash, you must realize that Lucifer has oversimplified fire considerably. Reconsidering Equation 1-1, you will notice that all of the products of combustion are gases. Where, then, do the ashes come from? You will recall that these equations are for the combustion of cellulose, and that wood is only mostly cellulose. When wood is heated anaerobically, it turns black as the water is driven off, leaving charcoal, or carbon, behind. When charcoal burns in air, the carbon combines with oxygen, producing the gas, carbon dioxide. But if you have ever used a charcoal grill, you may have noticed that charcoal turns white as it burns. This white ash is what remains of the non-flammable minerals which were present in the wood to begin with. You don't really notice them until the carbon has burned away. These ashes have a composition which varies according to the kind of wood and the soil in which it grew, and it is this variable composition which marks ash as a mixture rather than a pure substance.

You will recall, no doubt, that a mixture can be separated into two or more pure substances by recrystallization, distillation, and chromatography. You will be pleased to learn that we are discussing only recrystallization in this chapter. You have, of course, noticed that some things, like salt and sugar, are soluble in water, while others, like sand and charcoal, are not. Recrystallization separates substances which differ in their solubility. Ash, for example, is mostly insoluble in water. Only a small portion of the ash dissolves in water, and this is the substance we call potash, or potassium carbonate. To make potash, you must add your ash to a quantity of water. Any leftover charcoal will float to the top, while the insoluble minerals will sink to the bottom. The good stuff, the potash, will be dissolved in the water. You must separate the water from the charcoal above and the minerals below. Once you have done this, you will have what looks like clear, clean water. But if you boil the water away, or let it evaporate in the Sun, a white, crystalline residue will remain. This residue is potash.

Table 8-1. Combustion Products of Beech Wood

Now, it is important, if you are to be successful, that your ashes have never been wet. If they have been wet before you started, then, of course, the potash will already have been washed out of them. So you must get your ashes from a fire that has been allowed to burn out, not from one which has been doused with water. But if your ashes were dry, and if you were careful to skim off the charcoal, and if you allowed the minerals to settle completely, and if you were able to collect the water without stirring up the sediment, and if, finally, you boiled away all the water, you will have nice, pure, white, crystalline potash, which is a lovely thing to behold.

This potash will look just like salt or sugar, so how will you know that it is not just salt or sugar? You will give it a taste. If your mother was as strict as mine, the taste will be

already know. Good choices are lemon juice, vinegar, baking soda, and soap. From this experience you will be able to use pH test paper to distinguish bitter things from sour things, alkalis from acids, without risking your health.

Before we get too much farther, I should tell you that potash, or potassium carbonate, is not the only soluble component of wood ash. Depending on the soil conditions, sodium carbonate may also be present. As a matter of fact, when the ashes come from burning seaweed, there may be more sodium carbonate than potassium carbonate, and in this case we refer to the product as soda ash. Table 8-1 [1] shows what happens to 1000 pounds of Beech wood when it is burned. Most of it is consumed in the fire, of course, producing gaseous water and carbon dioxide. Less than six pounds of ash remain. Most of this ash is not soluble. When the water is boiled from the soluble bit, a little over a pound of crude potash remains. As I have explained, most of this crude potash is potassium carbonate, but some of it will consist of sodium carbonate, potassium sulfate, and other soluble compounds. You may be wondering how you could remove these contaminants. I am happy you asked.

Table 8-2. Solubility of Alkali Sulfates and Carbonates

Adam, I must tell you, has considerably simplified the whole business of solubility. Solubility is not a black-and-white issue; some "soluble" compounds are more soluble than others. Table 8-2 shows that potassium carbonate has a much higher solubility than the other compounds we might expect to be present in wood ashes. If, instead of boiling away all the water, we were to boil away only most of the water, the less soluble compounds would precipitate, that is, they would sink to the bottom of the solution as solids, and the potassium carbonate would stay in solution until the last possible moment. If we were to pour off this solution and boil it to dryness, the resulting solid would have fewer contaminants than the crude potash.

Well, really, we have done the same thing to remove the sodium carbonate and potassium sulfate that we did to remove the insoluble ash. In both cases we are physically separating compounds that differ in their solubility. This process, known as recrystallization, remains the most widely-used technique for purifying solids.

Figure 8-1. Recrystallization as a Process

Figure 8-1 illustrates the recrystallization process in schematic form. The first reactor, the lixiviator, is a container in which part of a solid is allowed to dissolve in water. In the next section, we will use our familiar 2-liter soft-drink bottle to lixiviate wood ashes. The second reactor, the furnace, should be familiar from Figure 1-3. A beaker in an oven will serve well for this. Unlike previous processes, there is no chemical reaction here. It is simply a physical process for separating things that differ in solubility. The usual conventions are followed; reactants come in from the left, waste products exit to the top and bottom, and the main product exits to the right.

You will be quite interested to know that Nature does some recrystallizing of her own. When a sea becomes land-locked, soluble minerals wash into it from the rivers and streams that empty into it. Eventually, the Sun dries up the water, and the least-soluble component precipitates, forming a bed of, say, salt. If the climate is more arid, soda ash may begin to precipitate, and if the sea dries up completely, a layer of potash may form on the top, providing that there was any potash in the river water to begin with. So an ancient sea-bed consists of beds of material which differ in their solubility. This makes it quite convenient for mining, since it saves you the trouble of quite a lot of recrystallization.

hydroxide anion. Only a tiny portion of the water falls apart in this way, but, it turns out, this tiny portion is extremely important. In pure water, of course, there are an equal number of hydrogen and hydroxide ions, since each water molecule gives one of each. For this reason, we say that pure water is neutral and assign it a pH of 7. Please notice that pH is spelled with a small p and a big H.

Figure 8-2. The pH Scale

Now, potassium carbonate falls apart into two potassium cations and a carbonate anion. The potassium ions float happily about the solution and take no further part in the chemistry for the moment. But if carbonate ion bumps into a water molecule, it may swipe a hydrogen ion from it, leaving a hydroxide ion behind. Alternatively, it may bump into a hydrogen ion, which may stick to it. In the first case, the number of hydroxide ions has increased. In the second, the number of hydrogen ions has decreased. In either case, there are now more hydroxide ions floating around than hydrogen ions and the solution is no longer neutral. We say that the solution is alkaline, or basic, and it gets a pH bigger than 7. The more basic a solution is, the bigger the number. A 10% potash solution, for example, has a pH of 10; a strongly alkaline solution can go as high as 14.