Chemistry 101

[Mercedes Benzene]

simple is fine, but I do like to give people Im teaching a 'heads-up' of whats to come. I used to hate it when teachers would give us a sheltered, semi-correct explanation for things..

 

You are more than welcome to help teach Jay-qu.:eek:

This isn't "my" classroom. :)

[Mercedes Benzene]

Okay, well, I'm about to go out with some friends, but I managed to put together a little "cheat sheet", that provides the valances of some select ions.

I'll attach is here, so you guys can look at it (see attachments).

The first page contains some basic ions as well as an activity series, which I will explain in another post when I cover single-replacement reactions.

The second page contains some more ions, mostly those of elements with variable oxidation states.

 

This is just a draft that I would like to eventually complete. If you find any mistakes, or if there are any ions that I missed (I'm sure there are a lot), please just PM me, or leave them in this thread.

 

Thanks! And I hope it helps those of you who would like to learn about ionic compounds!

[IDMclean]

Short Question: How is the number of electrons determined? Why is it that Chlorine has seven? Number of protons right?

[Jay-qu]

Chlorine in its neutral ground state will have 7 valence electrons and 17 electons total, it has 17 protons.

[Chemnut]

what are the purpose of positive and negative charged particles in chemistry? I mean how do they differ from particles with no charge, and what can you use them for?

This (charged particles) is the world of chemistry. Without charged particles, there would be no electrostatic attractions , no reactions, no intense colored transition metal solutions, no rusting of metal, etc. The world would be very boring without all this.

[Chemnut]

I did many chemical separations using ion exchange resins (Another use of ions or charged particles). These ions, that made the ion exchange possible, were generally the anions of strong and weak acids. This leads me into another area of ions.

 

Place the following acids in order of increasing acidity (Assume standard temperature, pressure and aqueous solutions).

 

H2SO4, HCl, H3PO4, HF, H2O

 

What is a strong acid? What is a weak acid? Why are these strong or weak or otherwise?

 

Many a Scientist has been stumped by a 6 year old kid that asked the question, Why?.

[hallenrm]

What is a strong acid? What is a weak acid? Why are these strong or weak or otherwise?

 

Many a Scientist has been stumped by a 6 year old kid that asked the question, Why?.

 

An acid is said to be stronger than another whe it produces more Hydrogen ions in an aqueous solution of same molarity. So a weak acid is one that is weaker in its capacity to produce hydrogen ions and thus its aqueous solution has a higher pH.

 

In the series that you have presented, I would offhand say that Water is the weakest acid.;)

[Mercedes Benzene]

Hallenrm is right.

Acids are said to be "strong" or "weak" depending on how fully the substance dissociates in solution.

Strong acids completely, or almost completely dissociate in solution.

In your series, the correct order (weakest to strongest) should be:

 

H2O, H3PO4, HF, H2SO4, HCl

 

I would double check on the H3PO4 and the HF though. They may need to be switched.

[learnin to learn]

what about acids and bases? which one is stronger?

[Mercedes Benzene]

You can't say that an acid or base is stronger.

They are completely different things!

 

The pH scale is a measure of the Hydrogen ion concentration in a given substance.

The pH scale ranges from 1 to 14.

The number 7 is neutral.

As the number increases past 7, the substance in more basic (or alkaline).

As the number decreases below 7, the substance is more acidic.

a pH of 1 would be extremely acidic.

a pH of 14 would be extremely basic.

 

now pH is simply the negative logarithm of whatever the concentration may be.

 

For instance, lets say a substance has a hydrogen ion concentration of .08

The pH can be determined thusly:

-log10(.08) = ~1.09

This would be a very strong acid.

 

On the other hand, if the ion concentration was 1.06x10^-13, when plugged into the equation:

-log10(1.06x10^-13) = ~12.97

That would be a fairly strong base.

[Chemnut]

In order of increasing acidity in water,

 

H20 > HF > H3PO4 > HCl > H2SO4

 

The acid dissociation constants, Ka, are 1 E-07, 6.8 E-04, 6.9 E-03, Large, Larger respectively. The larger the Ka, the stronger the acid.

 

The acid dissociation constant is a measure of the degree of ionization or how many ions are formed or how many ions dissolve in water.

 

pH is a measure of the molar concentration of Hydrogen ion in solution (hydronium ion). The pH scale is commonly displayed as 1 to 14. pH paper (generally a single indicator) and pH sticks (often 4 or more indicators) use indicators or substances that change color with changes in the H+ or the OH- concentration. These indicators typically change colors between pH 1 and 14.

 

The rule for pH is pH + pOH =14. It is possible to have pH < 0 or > 14.

 

I know of 3 definitions of acids. Each should be kept in mind when discussing acids.

 

Arrhenius—An acid is a substance that, when dissolved in water, increases the concentration of the hydrogen ion (H+ ).

 

Bronsted-Lowry—A substance that can donate a proton (H+).

 

Lewis—A species or substance that forms a covalent bond (sharing of electrons) by accepting an electron pair.

 

So, Why is HF a weak acid? If you look at the strengths of the other halide acids, they increase as you go up the periodic chart. HCl is a stronger acid than HBr which is stronger than HI.

 

Learning, is sometimes like asking a fireman holding a 4 inch hose for a drink of water.

[IDMclean]

Ok why do we need to know that? What purpose does it serve to know this information? What can I do with this?

 

Perhaps an example of a Acid or Base in use would be prudent. I have heard of testing and adjusting the PH of the ground that you use for planting.

 

What are some other chemistry synergies, where will this play an important role in future lessons?

[Jay-qu]

Yes plants will be best grown in a certain pH soil, another example is swimming pools and other water sources, the pH can tell you about whats going on in the water.

[Chemnut]

The pH of your blood must be within the 6.8 to 7.8 range to sustain life.

The pH of your bile(stomach) acid (hydrochloric acid) ranges between 1 and 3.

The pH of Pepsi, Coke, and other colas (read the ingredients on the can for all the acids in the soda), and lemon juice(citric acid) is around 2.2. The pH of most soda pop (carbonic acid) is about 4. The pH of beer is 4-4.5. The pH of milk (contains lactic acid) is 6.4.

 

In order to ship or transport liquid products as non hazardous, the pH of the solution must be > 2 and < 10. Whether it is shiping new products or determining is waste is hazardous or not or government agencies monitoring compliance to a rule or the general public or watchdogs monitoring government agencies or powerplant emissions or monitoring of commercial industry, many people are employed by this regulation.

 

Potable water supplies are also regulated and pH is monitored.

 

The more sour the taste, the more acidic it is, the lower the pH. Many food, candy and juice companies regulate the acidity of the product to maintain freshness and taste. Most of the acids in foods, are weak acids. They are often used as preservatives.

 

Vegetation grows in pH range about 5.5 to 8.5.

 

A few common household items that are acidic are: bleach (hypochlorous acid), toilet bowl cleaners, drain cleaners, vinegar (acetic acid). All weak acids.

 

A few common household items that are basic are: Ammonia, many cleaners, baking soda (sodium bicarbonate), some oven cleaners and soaps that contain Lye (sodium hydroxide a strong base).

 

Safety professionals have the job of ensuring worker safety during the manufacturing and use of chemicals including acids and bases.

 

If this post gives you a headache, you can take Aspirin (acetylsalicylic acid).

If it turns your stomach, you may take a weak base to sooth it such as Tums (Calcium Carbonate) or Mylanta or Rolaids etc.:hyper:

[IDMclean]

So what happens when I mix an extreame with a weak?

 

Also don't acids and bases cause state changes to things they are exposed to?

 

Check: If I take an equal base and mix it with an equal acid then they neutralize?

[Turtle]

A few common household items that are acidic are: bleach (hypochlorous acid), toilet bowl cleaners, drain cleaners, vinegar (acetic acid). All weak acids.

 

A few common household items that are basic are: Ammonia, many cleaners, baking soda (sodium bicarbonate), some oven cleaners and soaps that contain Lye (sodium hydroxide a strong base).

 

Wonderful post Chem! On topic, moderate length, informative, & with a twist of humor. My only quibble (and a minor one at that:lol: ) is that most drain cleaners contain sodium hydroxide & so are base not acid. (Drano brand crystal drain opener for example.) Not only does sodium hydroxide break down hair & grease, it won't harm the pipes.:)

[Mercedes Benzene]

So what happens when I mix an extreame with a weak?

 

Also don't acids and bases cause state changes to things they are exposed to?

 

Check: If I take an equal base and mix it with an equal acid then they neutralize

 

-Nothing in particular happens when you mix an extreme with a weak. Some "mixed" acids can display some interesting characteristics. For instance, aqua regia was the archaeic name for a mixture of concentrated nitric acid and hydrochloric acid. This was important because it was able to dissolve substances that could not previously be dissolved: such as gold!

 

-I'm not sure... I have never heard that one. Acids dissolve... but I don't think they cause state changes.

 

-Be careful when you say "equal". Yes, acids and bases neutralize to produce a salt and water... Since it is nothing but a simple double displacement reaction, then the "equal" you refer to means that as long as there are enough ions to react, then the reaction will happen completely. You do not have to have acids and bases of equal molarity or relative strength to react.

 

:)