POTASH
So we have been frolicking about nature and have now run our curiosities to things that many of your journal questions have pointed to... now that we have found all these wonderful things in the wilderness, what if we start combining them? I have burnt this fire, and it is good to cook meat, but is there anything useful I can do with the ashes other than color on the walls the fact that my daughter has a skirt?
In fact our tribal cave-dunce was playing in the dirty fire ring and has figured out something useful, while playing with the ashes he was able to make his hands clean instead of dirty. Certainly something that wasn't expected by the rest of us geniuses smart enough to stay out of the dirty remains of the fire. Remember how we talked about purity in the FIRE section? And that the wood itself was not pure? The primary things left behind in the ashes are potassium carbonate (potash) and sodium carbonate (soda ash). Referencing your periodic table you will find that both SODIUM (Na) and POTASSIUM (K) are placed in the same vertical group. (Label your periodic table with this group name now). This is done because they have similar properties which give them similar behaviors and appearances, so similar in fact that we have known about them since we first found ashes, but weren't able to tell them apart until the 1800's when industrialization was well under way and the United States was an independent country (1783 ended the war that began in 1775 at the battle of Lexington).
What we effectively discovered was our first base, which most of you know something about as "that thing that neutralizes acids." It is sometimes referred to as an alkali (the GROUP name given to the first vertical group on the periodic table) and its chemical function is to remove Hydrogen ions from aqueous solutions. Realizing this discovery is the first step to making soap, bleaching that funky animal wool, and making glass.
In fact our tribal cave-dunce was playing in the dirty fire ring and has figured out something useful, while playing with the ashes he was able to make his hands clean instead of dirty. Certainly something that wasn't expected by the rest of us geniuses smart enough to stay out of the dirty remains of the fire. Remember how we talked about purity in the FIRE section? And that the wood itself was not pure? The primary things left behind in the ashes are potassium carbonate (potash) and sodium carbonate (soda ash). Referencing your periodic table you will find that both SODIUM (Na) and POTASSIUM (K) are placed in the same vertical group. (Label your periodic table with this group name now). This is done because they have similar properties which give them similar behaviors and appearances, so similar in fact that we have known about them since we first found ashes, but weren't able to tell them apart until the 1800's when industrialization was well under way and the United States was an independent country (1783 ended the war that began in 1775 at the battle of Lexington).
What we effectively discovered was our first base, which most of you know something about as "that thing that neutralizes acids." It is sometimes referred to as an alkali (the GROUP name given to the first vertical group on the periodic table) and its chemical function is to remove Hydrogen ions from aqueous solutions. Realizing this discovery is the first step to making soap, bleaching that funky animal wool, and making glass.
CREDIT FOR THIS SECTION
1. Journal credit.
-You have evidence of detailed notes -50 points -You have a summary of key points (paragraph form) 25 points -You have further questions that are not answered in the notes. 1 question- 5 points 2 questions 15 points 3 questions 25 points *these questions SHOULD NOT BE answerable by the notes *these questions SHOULD NOT BE common knowledge (or common sense) |
2. POTASH Quiz
This will consist of 3 questions on any topic discussed below such as: any chemical formula given, the difference between potash and soda ash, the difference between an acid and a base, what litmus paper does, where alkali metals are on the periodic table, what recrystallization is and how its used, saturated vs supersaturated vs unsaturated, any highlighted vocabulary (like precipitate) You may retake quizzes once per class until they are passed or the grading period closes. **You may only take one quiz per class period**
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3. Potash Project
This project can be done in class using the hot plates, beakers, etc if you so choose. If you are behind, you may want to do this project at home and bring it in. ALL PROJECTS MUST TURN LITMUS PAPER BLUE. To check if it will turn litmus blue at home you can taste your product, but only a tiny amount... it should taste bitter, like soap. 100: 1.00 gram of grey or white or pink-orange potash 90: 0.90 gram of grey or white or pink-orange potash 80: 0.75 gram of grey or white or pink-orange potash 70: 0.50 gram of grey or white or pink-orange potash 50: your potash has signs of contamination |
Chemistry of Potash
It would be useful to know that all ALKALI METAL compounds are soluble in water, that is to say that they will dissolve and form a solution. We will talk more about that later, but we will definitely take advantage of it now. Here's how: when an ionic compound dissolves in water it dissociates into its ions, that is how this type of compound gets its name. Take a look at our potash (potassium carbonate):
K2CO3(s) -----> 2 K+(aq) + CO3 2-(aq)
So now that we have thrown our solid potash into the water, we have created two ions and get the little "aq" symbol to show this as different from being a solid. These are not yet classified as new substances because if you were to remove the water, these ions would find each other and you would still have your potash. You should also recall from FIRE that the chemical equation represents parts. Notice we now have a big 2 in front of our potassium (K) on the product side of the arrow. We now make 2 parts K+ for every one part CO3 2-. Where the + and the - show the electrical charge balance... we'll get more into that later.
So how then, if we can't see it and so many of our rocks and ashes look similar to each other do we tell them apart? We apply litmus test paper. Litmus is one of the oldest forms of pH indicator (pH being the strength of an acid or base). We simply get a strip of test paper and touch it to the solution, if its an acid it turns red, if its a base it turns blue, if its neutral there is no change in its color and it remains its original pale yellow.
K2CO3(s) -----> 2 K+(aq) + CO3 2-(aq)
So now that we have thrown our solid potash into the water, we have created two ions and get the little "aq" symbol to show this as different from being a solid. These are not yet classified as new substances because if you were to remove the water, these ions would find each other and you would still have your potash. You should also recall from FIRE that the chemical equation represents parts. Notice we now have a big 2 in front of our potassium (K) on the product side of the arrow. We now make 2 parts K+ for every one part CO3 2-. Where the + and the - show the electrical charge balance... we'll get more into that later.
So how then, if we can't see it and so many of our rocks and ashes look similar to each other do we tell them apart? We apply litmus test paper. Litmus is one of the oldest forms of pH indicator (pH being the strength of an acid or base). We simply get a strip of test paper and touch it to the solution, if its an acid it turns red, if its a base it turns blue, if its neutral there is no change in its color and it remains its original pale yellow.
Recrystalization
You should remember from STONE that crystals are an indicator of purity, and that we can grow these crystals by slowly evaporating water solutions or quickly cooling molten mixtures. Since we can't tell them apart, this is how we'll get them separated and purify the things we want from the things we don't want. We need to ensure that our starting materials are pure or our products won't be and could give unintended consequences such as medicine killing you instead of curing your illness. Recrystallization is the technique of choice for purifying solids, regardless of whether they are a pure element (like Silver: Ag) or a compound such as potash (potassium carbonate K2CO3).
So here's how it works... everyone knows that when you make Kool-Aid we add sugar and it dissolves. And most of us add more sugar than the directions indicate and it all dissolves too. Eventually, there comes a point where no more sugar dissolves and this is called saturation. Once the solution is saturated, any attempt to add more sugar will see the sugar fall to the bottom of the pitcher. Lucky for us, different substances have different solubilities, consider the table below:
So here's how it works... everyone knows that when you make Kool-Aid we add sugar and it dissolves. And most of us add more sugar than the directions indicate and it all dissolves too. Eventually, there comes a point where no more sugar dissolves and this is called saturation. Once the solution is saturated, any attempt to add more sugar will see the sugar fall to the bottom of the pitcher. Lucky for us, different substances have different solubilities, consider the table below:
So what this shows us is that if we use a 100 mL beaker of cold water we can dissolve a LOT MORE potassium carbonate than any other material listed. If we start to evaporate the water, the solutes become more concentrated and our once unsaturated solution becomes saturated in the least soluble material present. Like the excess sugar in the Kool-Aid, this material starts to fall to the bottom and they are deposited in reverse order of solubility. Incidentally, this is also useful in determining the dates of ancient lake beds and is great for mining since everything is in nice layers. We can also help ourselves out by using hot water to start with (which is how all the fast food places make their sweet tea super sweet) to dissolve MORE than we normally could using cold tap water. We call this supersaturated.
You should recognize from your life experiences that when we burn cellulose (wood) there is relatively little ash left behind. You should also know from FIRE that the impurities left behind are what makes up the ashes and that within these ashes only a small portion of this is due to potassium and sodium carbonates. These carbonates were actually converted thanks to the carbon dioxide created by the fire, while there are other things going on, modern synthesis is done according to the equation 2KOH + CO2 → K2CO3 + H2O.
Making pot-ash.
Safety and Common sense: Just because these are 'natural' doesn't mean they are safe and this is an often misleading tactic in food marketing. Likewise just because they are 'chemicals' doesn't make them dangerous. As you start your purification, these things require a bit more handling caution than they do when they are in a dry mixture or a solution. You can find the MSDS (Material safety data sheet) for both of these here: potassium carbonate and sodium carbonate. A long story short is that if you get it on your skin, wash it off. If you get it in your eyes, flush them with water and go to the emergency room. If you're silly enough to eat spoon-fulls of it, it was nice knowing you, call the poison control center at 214-590-9016. All that being said... a quick taste by touching a small amount to your tongue won't hurt you.
PROCEDURE: Start by gathering your materials, a few handfuls of WOOD ashes THAT HAVE NEVER BEEN WET (if you use wet ashes the stuff we're looking for will have already dissolved and washed away and you will be wasting your time...likewise if you use charcoal ash you're wasting your time), some water, an empty 2L bottle, a glass beaker, and a spoon or glass rod. If you're doing this at home a pot will do instead of a beaker, but if its aluminum your parents will end you as it will not only ruin your project but also their pan because alkali (strong bases) reacts quite strongly with aluminum.
Fill the bottle with ashes until it is about 1/2 full. Add hot water, put the cap on the bottle, and shake vigorously. If you happen to be baby sitting this is a good time to get some energy out of the kids. After a good shaking... leave the bottle to settle out overnight and ensure it lies undisturbed. Our soluble carbonates (those with alkali metals in them) will dissolve and so will anything else in your ash that happens to be soluble. The remaining silicates (remember those from stone?) and insoluble carbonates (those not with your alkali metals) will settle on the bottom. Any remaining charcoal will float to the top. You just took advantage of all that middle school science referring to density and buoyancy as well as some recent science regarding solubility.
At this point, the water between the sediment at the bottom and the charcoal at the top should appear as if its clean and clear (which of course it is not clean and you should not drink it). Remove the cap and squeeze the bottle (over a sink) until the charcoal floating in the top comes out of the bottle. SLOWLY pour the water out of the bottle into your pot or beaker, if it looks like the sediment will pour out stop as you are trying to separate the materials and will contaminate your product. You can do a quality control check here by dipping your finger in and tasting the water, if it is bitter you are doing this right, if it isn't you should probably start over.
Place the glass rod into your beaker (or spoon into your pot), this will help prevent splattering caused by superheating. Boil the water until all of the water has evaporated. You should have a fine gray powder left behind, and some scale (the same stuff you have to clean out of the shower since we have 'hard water' here in Mesquite.) Let this cool and then scrape it out into a container. This is your product and contains all of the soluble minerals that were present in the ashes and the water you used, it might include a number of dissolved things, which is why it won't look like the picture on the webpage or internet.
Fill the bottle with ashes until it is about 1/2 full. Add hot water, put the cap on the bottle, and shake vigorously. If you happen to be baby sitting this is a good time to get some energy out of the kids. After a good shaking... leave the bottle to settle out overnight and ensure it lies undisturbed. Our soluble carbonates (those with alkali metals in them) will dissolve and so will anything else in your ash that happens to be soluble. The remaining silicates (remember those from stone?) and insoluble carbonates (those not with your alkali metals) will settle on the bottom. Any remaining charcoal will float to the top. You just took advantage of all that middle school science referring to density and buoyancy as well as some recent science regarding solubility.
At this point, the water between the sediment at the bottom and the charcoal at the top should appear as if its clean and clear (which of course it is not clean and you should not drink it). Remove the cap and squeeze the bottle (over a sink) until the charcoal floating in the top comes out of the bottle. SLOWLY pour the water out of the bottle into your pot or beaker, if it looks like the sediment will pour out stop as you are trying to separate the materials and will contaminate your product. You can do a quality control check here by dipping your finger in and tasting the water, if it is bitter you are doing this right, if it isn't you should probably start over.
Place the glass rod into your beaker (or spoon into your pot), this will help prevent splattering caused by superheating. Boil the water until all of the water has evaporated. You should have a fine gray powder left behind, and some scale (the same stuff you have to clean out of the shower since we have 'hard water' here in Mesquite.) Let this cool and then scrape it out into a container. This is your product and contains all of the soluble minerals that were present in the ashes and the water you used, it might include a number of dissolved things, which is why it won't look like the picture on the webpage or internet.
BONUS CERTIFICATE--15 points
To purify this product, recrystallize it again. This time you would start with only the product you just made instead of the ashes, dissolve it, boil it until ALMOST dry and filter it (you can use a coffee filter) while its hot to remove any materials LESS soluble than the carbonates you are trying to purify (refer to the table above). This time, you would also need to watch it while it cools as the carbonates will precipitate out (like rain) leaving anything more soluble that might be present still in the solution. By doing this over and over you can even separate the extremely similar sodium carbonate from the potassium carbonate. If you are successful, it should be white instead of grey.
To purify this product, recrystallize it again. This time you would start with only the product you just made instead of the ashes, dissolve it, boil it until ALMOST dry and filter it (you can use a coffee filter) while its hot to remove any materials LESS soluble than the carbonates you are trying to purify (refer to the table above). This time, you would also need to watch it while it cools as the carbonates will precipitate out (like rain) leaving anything more soluble that might be present still in the solution. By doing this over and over you can even separate the extremely similar sodium carbonate from the potassium carbonate. If you are successful, it should be white instead of grey.