Acids, Bases, & pH

One of the most interesting parts of chemistry is the study of acids and bases. It's also a very practical aspect of chemistry, since we use acids and bases every day! For instance, although "acidic" probably doesn't spring to mind when you bite into a tomato, you're actually tasting acidic juice. One of the characteristics of acids is that they taste sour. Bases, on the other hand, have a bitter taste. The sour or bitter taste is one of the easy ways to tell whether a food or drink is acidic or basic, although it's not safe to use the taste test with other things.

When dissolved in water, acids donate hydrogen ions (H+). Hydrogen ions are hydrogen atoms that have lost an electron and now have just a proton, giving them a positive electrical charge. Bases, on the other hand, mixed with water yield hydroxide ions (OH-). If a solution has a high concentration of H+ ions, then it is acidic. If a solution has a high concentration of OH- ions, then it is basic.

In many acid-base reactions, the resulting product is water along and a salt. If hydrochloric acid (HCL) and the base sodium hydroxide (NaOH) are combined, the product is H2O (water) and NaCl (sodium chloride, a table salt). The H+ ions in the acid join with and are neutralized by the OH- ions of the base to form H2O.

One of the simplest activities to show how acids and bases react with each other (and to demonstrate their different properties) is to make a baking soda and vinegar "volcano". To make a big eruption, use a small plastic bottle (the size 20-oz soft drinks come in works well). Fill the bottle halfway (1 to 1.5 cups) with vinegar. To start the eruption, drop a baking soda "bomb" into the bottle--wrap one tablespoon of baking soda into a small piece of tissue paper, tying the ends with thread. You should see an instant eruption! The baking soda, a base, neutralizes the acid in vinegar. This releases carbon dioxide gas, which causes the fizzing action in your volcano. (An acidic solution is neutralized when a base is added to it, and a basic solution is neutralized by the addition of an acid.)

For another reaction experiment, put an Alka-Seltzer tablet in the bottom of a clear plastic film canister (the kind where the cap fits inside instead of closing over the outside). Fill the canister with warm water and then quickly put the cap on and watch the acid-base reaction.

The pH scale is used to measure the amount of H+ ions in a solution. Acids have a pH below 7; bases have a pH above. Strong acids have the lowest pH levels (0-4) and strong bases have the highest pH levels (10-14). Neutral solutions have a pH of 7 and they are neither acidic nor basic. Distilled water is neutral, because the H+ and OH- ions are balanced.

Litmus is a natural acid-base indicator extracted from a type of lichen. If you have red and blue litmus paper, you can test different solutions for whether they are acids or bases. Blue litmus paper turns red when a solution is acidic; red litmus paper turns blue in basic solutions. Try testing window cleaner, toilet bowl cleaner, orange juice, and apple juice--pour a little of each into separate test tubes or small glasses or jars. Use the litmus paper to determine which are acids and which are bases. Here are the pH levels of some other substances that you might test: lemon juice (2), vinegar (3), milk (6), egg whites (8), baking soda (9), and ammonia (10). Human blood has an ideal pH of 7.4; even slight fluctuations can seriously affect our bodies.

You can also make your own pH indicator--use a blender to mix one part chopped red cabbage with two parts boiling water and use the juice to test different solutions. Acids will turn the pigments in the indicator to a reddish color; bases will turn the pigments bluish or yellow-green.

Good Water

Water may seem plain and boring sometimes, but it does have some interesting physical properties! Water weighs about 62 pounds per cubic foot at its freezing point; it freezes at 0° Celsius and boils at 100° ; and it makes up about 60% of the composition of our bodies and 83% of our blood! As for what it can do, water is called the "universal solvent" because it can dissolve more substances than any other liquid, even the strongest acid.

The chemical composition of water is H2O--two hydrogen atoms and one oxygen. The way those atoms bond together to form a water molecule is what allows water's special properties. The two H atoms form weak hydrogen bonds with the oxygen; they attach to the top of the molecule rather like Mickey Mouse ears.



This molecular structure gives the water molecule polarity, or a lopsided electrical charge that attracts other atoms. The end of the molecule with the two H atoms is positively charged. The other end, with the oxygen, is negatively charged. Just like in a magnet, where north poles are attracted to south poles (opposites attract), the positive end of the water molecule will connect with the negative end of other molecules.

Water is the only natural substance that can exist in all three states of matter--solid, liquid, and gas--at the temperatures normally found on Earth. Many other substances have to be super-heated or -cooled to change states. The solid state of water (i.e., ice) is less dense than the liquid state, which is why ice floats.

Polar substances dissolve easily in water, the "universal solvent". That is because one end of a polar molecule is more positively charged and one end is more negatively charged. The positively charged end of a polar molecule will be attracted to the negatively charged end of a water molecule, and vice versa. Likewise, positive ions are attracted to the negative end of the water molecule and vice versa. This molecular attraction is what allows so many substances to dissolve easily in water--the molecules are surrounded by water molecules. Oil and other non-polar solutions do not have positively or negatively charged ends, so water molecules will be attracted to each other rather than the oil. This is why oil does not mix with water.

Weight Percent (Wt%) Solutions

One common solution is based on weight percent. The weight percent of a solution is the weight of chemical divided by the total weight of the solution (chemical + water) and multiplied by 100. Since the density of water is 1 g/ml, the formula to calculate the amount of chemical that must be mixed for a wt% solution is:

grams of chemical = (wt% solution) x (ml of water) ¸ (100 - wt% solution)

As an example, to make 100 ml of 10% NaCl (table salt) solution, dissolve 11.1 g NaCl in 100 ml 0f water:

grams of NaCl = 10 wt% x 100 ml water ¸ (100 - 10 wt%) = 11.1 g

Molar Solutions

Molar (M) solutions are based on the number of moles of chemical in 1 liter of solution. A mole consists of 6.02x1023 molecules or atoms. Molecular weight (MW) is the weight of one mole of a chemical. Determine MW using a periodic table by adding the atomic mass of each atom in the chemical formula. Example: For the MW of CaCl2, add the atomic mass of Ca (40.01) to that of two Cl (2 x 35.45) to get 110.91 g/mole. Therefore, a 1 M solution of CaCl2 consists of 110.91 g of CaCl2 dissolved in enough water to make 1 liter of solution.

Once the molecular weight of a chemical is known, the weight of chemical to dissolve in water for a molar solution is calculated by the formula:

grams of chemical = (molarity of solution, mole/liter) x (MW of chemical, g/mole)

x (ml of solution) ¸ 1000 ml/liter

As an example, to make 100 ml of 0.1 M CaCl2 solution, dissolve 1.11 g of CaCl2 in sufficient water to make 100 ml of solution. The amount of water needed will be slightly less than 100 ml.

grams of CaCl2 = (0.1 mole/liter x 110.91 g/mole x 100 ml¸ 1000 ml/liter) = 1.11 g

Thanx jam, that's very helpful and straight-forward info, especially for a new bee like myself. I think it's a good idea to experiment with common household chemicals first, like in your example of acid/bases with vinegar and baking soda, before rushing headlong into a complicated synthesis using dangerous and watched chemicals.

I got a question about pH. Is there a way to tell when a solution becomes basic or acidic without the use of a pH meter or paper? For example, you got your alkaloids sitting in a solution of vinegar and water, your adding baking soda to the solution slowly, is there a way to tell when the solution becomes basic just by observation without a pH meter or litmus paper?

Well the action of an acid/base reaction produces a salt when the solution goes from being basic to acidic.

So when the substance which has been basified is acidified to the necessary PH it would visiually form into a salt and that would be a process from which you could observe as the transformation takes hold.

Jam.

http://chemlearn.chem.indiana.edu/demos/RedCabba.htm

this is what chemistry 101 gets you

The facts giving rise to this offence appear in an agreed statement of facts tendered during the plea. On 19 February 1997 a fire occurred at a house at 9 Downes Street, Brunswick. Firefighters at the premises drew the attention of police to containers of chemicals in the driveway and rooms that contained an assortment of glass vessels and piping apparently set up as some sort of laboratory. Scientists from the Victoria Forensic Science Centre then examined the premises on 20 February and found a large quantity of chemicals, glassware and apparatus consistent with the manufacturing of methylamphetamine. There were chemical drums and containers in the hallway of the house and two large reaction vessels fitted with condensers and hosing seated in heating mantles on a washing machine at the rear of the house. White plastic drums containing liquid with separating funnels sitting on top of them were found and further chemicals were located in a bungalow attached to the rear porch area.



The house had been owned by the applicant's father, George Edward Howden since 1958, and occupied by him until 1995. Since then it had been generally unoccupied but the applicant had been paying the utility accounts for the house, had changed the locks and was renovating the premises.



A scientist from the Victoria Forensic Science Centre gave evidence that in the vessels and containers found in the premises liquid containing methylamphetamine was found and that the quantity of methylamphetamine present was 28.65 kilograms. The applicant's fingerprints were found in the doorway and on the passenger window of a Tarago van found in the driveway of the premises and on two reaction vessels located in heating mantles. The applicant had been seen by various persons going to 9 Downes Street.



The fire at the premises was probably caused by the ignition of acetone and/or other volatile organic solvent vapours within the kitchen. There were open containers found in the kitchen that could have allowed a build-up of vapour within the premises particularly on a day when the temperature had been approximately 40 degrees celsius.



Meanwhile the applicant himself had on 19 February 1997 attended at the Emergency Department of the Preston and Northcote Community Hospital with burns to approximately 30% of his body. He had burns to his upper arms (front and back), both hands (front and back) and extensive burns to both legs (front and back) and left foot. The applicant at first refused to explain how he had sustained his injuries but later on 19 February said his burns had been caused by acetone. Later still he said his injuries had been caused while doing welding work during which an acetone solution had caught fire. The clothes he was wearing at the time were taken away for examination and in the rinsing of his shorts and underpants, methylamphetamine, pseudoephedrine (or ephedrine), amphetamine and two naphthalene derivatives were found. The applicant was transferred to the Alfred Hospital Burns Unit where he was treated for some weeks. He made "no comment" answers when interviewed by the police but was ultimately charged with trafficking in methylamphetamine.



During the second half of 1997 police received information that a quantity of methylamphetamine was stored in the yard area of premises used by the applicant at 14 Main Street, Coburg. After entry to the premises had been obtained and samples taken, a sample of powder found in plastic bags within a barrel on a shelf on the premises tested positively for methylamphetamine. After further surveillance, the applicant was observed on 3 December 1997 to visit the yard. He was seen to unlock the gates of these premises and proceed directly to the barrel stored on the shelf. He removed something from the barrel and placed it inside his left sock. He replaced the lid and put the barrel back on the shelf. Upon leaving the premises and closing the gates he was arrested, and a small plastic snap-seal bag containing powder was found in his left sock. A search of the premises was then conducted and the items found included approximately 13.5 kilograms of powder containing methyl-amphetamine at approximately 40% purity and 10 kilograms of powder containing methylamphetamine at approximately 80% purity, approximately 38 kilograms of red phosphorous, two empty 20-litre containers of acetone and various other implements. The analysis of the powders located at these premises indicated that the total quantity of pure methylamphetamine present was 12.6 kilograms.



The applicant was subsequently interviewed by the police and again made "no comment" answers to the allegations put to him. He was again charged with trafficking in methylamphetamine.



The total quantity of pure methylamphetamine the subject of the count to which the applicant pleaded guilty was 41.25 kilograms. At the relevant time the commercial quantity of methylamphetamine for the purposes of s.71(1)(a) of the Drugs Poisons and Controlled Substances Act 1981 was 2 kilograms pure. The estimated value of the amount of methylamphetamine the subject of the charge is $6,352,500 if sold in pound amounts without dilution or $78,059,520 if sold at street level purity of 3% at $60 per gram.



didnt this guy have a stab at the big time...

if the guy had that much game, wtf was he doing at a house in town?

edit: sucks to see the guy get popped for being creative but given the current legal situation with meth, that story seems like a case of the gene pool getting skimmed

[This message has been edited by Symbiote (edited 01-29-2004).]

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