03/05/2021
Acid
a chemical substance that neutralizes alkalis, dissolves some metals, and turns litmus red; typically, a corrosive or sour-tasting liquid of this kind.
Chemistry
a molecule or other entity that can donate a proton or accept an electron pair in reactions.
Arrhenius Acid
An Arrhenius acid is a molecule that when dissolved in water will donate an H+ in solution. Simply put, a proton donor.
The trick to recognizing an Arrhenius acid is to look for a molecule that starts with an H, and typically contains an oxygen or halogen.
Common examples of Arrhenius acids include:
Hydrochloric Acid – HCl
Nitric Acid – HNO3
Sulfuric Acid – H2SO4
Acetic Acid – HCH3CO2
and so many more…
An acid dissociating in water does not form a free-floating proton. Instead one of the water molecules in solution will grab the H+ yielding a hydronium or H3O+ ion. Here’s what happens when nitric acid dissociates in water.
Arrhenius Base
An Arrhenius base is a molecule that when dissolved in water will break down to yield an OH- or hydroxide in solution. To recognize the Arrhenius base look for a molecule ending in OH, but not following CHx which refers to an alcohol.
Arrhenius base examples include:
Sodium hydroxide – NaOH
Potassium hydroxide – KOH
Magnesium hydroxide – Mg(OH)2
and so many more…
Bronsted-Lowry Acid
A Bronsted-Lowry acid, like an Arrhenius acid, is a compound that breaks down to give an H+ in solution. The only difference is that the solution does not have to be water. We can still refer to the exact same acids as listed for the Arrhenius acid examples, but this time we’ll change the solvent to ammonia, alcohol, or anything else.
We saw what happens when nitric acid (HNO3) dissolves in water. Now let’s see what happens when it dissolves in ammonia (NH3) or even methanol (CH3OH)
Nitric acid still dissolved to yield an H+ and NO3-, but this time it was NH3 and not water that picked up the free-floating proton.
Bronsted-Lowry Base
This is where we start to see the difference between the Bronsted-Lowry and Arrhenius definitions. While the Arrhenius base referred specifically to the hydroxide (OH-) ion, the Bronsted-Lowry base refers to any atom or ion capable of accepting or bonding to a free proton in solution.
Referring back to the HNO3 + NH3 reaction above, when ammonia picks up the free H+ it acts as a proton-acceptor. NH3 is the Bronsted-Lowry base in this example.
Additional examples include:
Methanol – CH3OH
Formaldehyde – H2CO
And even water – H2O
Lewis Acids and bases
The Lewis definition for acids and bases is the most extreme because it’s not dealing with protons specifically. Instead the Lewis definition deals with the movement of electrons.
Lewis Acid/Base Mnemonic
Think of Lewis as ‘lectrons’
Lewis Acid
A Lewis acid refers to an atom or molecule that accepts an electron pair. Think back to your ‘pushing arrows’ for orgo mechanisms. Every time you draw an arrow representing the movement of electrons, the atom getting attacked or accepting those electrons is the Lewis acid in that reaction.
Common Lewis Acid Examples in Organic Chemistry
Borane – BH3 (hydroboration reaction)
Aluminum Chloride – AlCl3 (electrophilic aromatic substitution reaction)
Iron (III) Bromide – FeCl3 (electrophilic aromatic substitution reaction)
Lewis Base
Since the Lewis definition has to do with the transfer of electrons, you can guess by now that a Lewis Base is an electron pair donor. Once again think back to your reaction mechanisms. The molecule using its electrons to attack another atom is an electron pair donor and a Lewis Base.
Types of acid
0rganic
Oxalic Acid : Tomato
Tartaric Acid : Tamarind
Malic Acid : Tea.apple
Citric Acid : Citrus Fruits
Lactic Acid : milk
Oxalic Acid : Tomato
Tartaric Acid : Tamarind
Malic Acid : Tea
Acetic Acid : Vinegar
In organic acid
Hydrochloric acid HCl.
Nitric acid HNO3
Phosphoric acid H3PO4
Sulfuric acid H2SO4
Boric acid H3BO3
Hydrofluoric acid HF.
Hydrobromic acid HBr.
Perchloric acid HClO4
PHYSICAL PROPERTIES OF ACIDS:
1. Acids have a SOUR taste
2. All acids are SOLUBLE in water
3. Acids solutions turn BLUE litmus paper RED
4. Acid solutions have a pH values < 7
5. Most acid solutions are CORROSIVE
6. All dilute acids CONDUCT ELECTRICITY due to the presence MOBILE IONS in solution
CHEMICAL PROPERTIES OF ACIDS:
1. React with reactive metals (above H in Reactivity Series) to form Salt & Hydrogen Gas
2. React with Metal Carbonates to form Salt, Carbon Dioxide & Water
3. React with Bases/Alkali to form Salt & Water (Neutralistion Reaction)
Uses of Acids:
1. Vinegar, used in the kitchen, is a liquid containing 3-6% acetic acid. It is used in pickles and in many food preparations.
2. Lemon and orange juice contains citric acid. Citric acid is used in the preparation of effervescent salts and as a food preservative.
3. Acids have been put to many uses in industry. Nitric acid and sulphuric acid are used in the manufacture of fertilizers, dyes, paints, drugs and explosives.
4. Sulphuric acid is used in batteries, which are used in cars, etc. Tannic acid is used in the manufacture of ink and leather.
5. Hydrochloric acid is used to make aqua regia, which is used to dissolve noble metals such as gold and platinum.
6. Sulphuric acid is used in manufacturing fertilizers such as super phosphate, ammonium sulpahte etc.
Expect base alkali nd pH scale next week
