First of all, what is pH? The pH scale is commonly used, and you've probably heard of it before, but what does pH really mean? Well, pH is actually equal to the negative log of the concentration of H+ ions in a solution, while pOH is equal to the negative log of the concentration of OH- ions in a solution. So a pH of 2 means that there are 10^-2 M of H+ ions. And since the pH and pOH must sum to 14, that also means that the pOH would be 12, meaning there are 10^-12 M of OH- ions. Ironically, this means that the lower the pH, the higher the concentration of H+ ions becomes. This also means that the concentration of H+ ions should multiply with the concentration of OH- ions to produce 10^-14. And basically, anything with a pH below 7 is considered acidic, while generally anything with a pH above 7 is considered basic, while 7 is neutral, which is where pure water usually sits.
Now, there are actually three common definitions for an acid and base, and these definition are connected in that each encapsulates the others. Visually, it's like this:
Now, there are actually three common definitions for an acid and base, and these definition are connected in that each encapsulates the others. Visually, it's like this:
Which means that, anything that is considered an Arrhenius acid/base is also considered a Bronsted Lowry acid/base, which is also considered a Lewis acid/base. However, not every Lewis acid/base is considered an Arrhenius one, which is kind of like the square and rectangle, where Arrhenius is the square and Lewis is the rectangle. Every square is a rectangle, but not every rectangle is a square. Now, what are the actual designations of each type?
Lewis:
Acid--Accepts electron pair
Base--Donates electron pair
Bronsted-Lowry:
Acid--Donates H+
Base--Accepts H+
Arrhenius:
Acid--Donates H+ in H2O
Base--Donates OH- in H2O
Now that that's clear, let's talk about some properties of acids and bases.
Acids:
- Turns litmus paper (a type of pH indicator) red
- Tastes sour (not that you should try to taste an acid in the lab)
- Strong acids may sting, or just feel wet
Bases:
- Turns litmus paper blue
- Tastes bitter or soapy (soap is a base after all)
- Feels slippery
Some common acids and bases that every student should at least be aware of:
7 Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO3, HClO4
(Note, HF is not a strong acid because of its hydrogen interactions. In the case of molecules like HClO3 and HClO4, the more oxygens, the more acidic it is.)
6 Strong Bases: LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
Weak Acids: CH3COOH, HF, HCN, H2S
Weak Bases: NH3, HS-, NH4OH, HS-
Neutralization reaction:
What happens when you combine an acid and a base? A strong acid with a weak base -> weak acid. A strong base with a weak acid -> weak base. Weak base with weak acid -> calculated with a more complex formula involving pKa that I won't discuss in this article. Strong base with strong acid -> Neutralization reaction -> neutral.
In a neutralization reaction a strong base is reacted with a strong acid which produces a neutral salt and water.
For instance, NaOH + HCl -> NaCl + H2O
This is a simple double replacement reaction combining NaOH (Strong base) with HCl (Strong acid) to produce a soluble salt NaCl (not always soluble, but this one is because of the Group 1 sodium) and water.
Applications:
Acid's sour property is used in foods like vinegar and lemon juice.
Used in manufacturing:
Sulfuric acid--batteries and fertilizers to make alkaline soils more suitable for plant growth
Calcium hydroxide--bleaching powder and dry painting mixes
Nitric acid--explosives, dyes, fertilizers, and paints
Phosphoric acid--soft drinks
Sodium hydroxide--soap, paper, and rayon
Acids and bases are also used in medicine, disinfectants, titrations, and indicators.
Lewis:
Acid--Accepts electron pair
Base--Donates electron pair
Bronsted-Lowry:
Acid--Donates H+
Base--Accepts H+
Arrhenius:
Acid--Donates H+ in H2O
Base--Donates OH- in H2O
Now that that's clear, let's talk about some properties of acids and bases.
Acids:
- Turns litmus paper (a type of pH indicator) red
- Tastes sour (not that you should try to taste an acid in the lab)
- Strong acids may sting, or just feel wet
Bases:
- Turns litmus paper blue
- Tastes bitter or soapy (soap is a base after all)
- Feels slippery
Some common acids and bases that every student should at least be aware of:
7 Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO3, HClO4
(Note, HF is not a strong acid because of its hydrogen interactions. In the case of molecules like HClO3 and HClO4, the more oxygens, the more acidic it is.)
6 Strong Bases: LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
Weak Acids: CH3COOH, HF, HCN, H2S
Weak Bases: NH3, HS-, NH4OH, HS-
Neutralization reaction:
What happens when you combine an acid and a base? A strong acid with a weak base -> weak acid. A strong base with a weak acid -> weak base. Weak base with weak acid -> calculated with a more complex formula involving pKa that I won't discuss in this article. Strong base with strong acid -> Neutralization reaction -> neutral.
In a neutralization reaction a strong base is reacted with a strong acid which produces a neutral salt and water.
For instance, NaOH + HCl -> NaCl + H2O
This is a simple double replacement reaction combining NaOH (Strong base) with HCl (Strong acid) to produce a soluble salt NaCl (not always soluble, but this one is because of the Group 1 sodium) and water.
Applications:
Acid's sour property is used in foods like vinegar and lemon juice.
Used in manufacturing:
Sulfuric acid--batteries and fertilizers to make alkaline soils more suitable for plant growth
Calcium hydroxide--bleaching powder and dry painting mixes
Nitric acid--explosives, dyes, fertilizers, and paints
Phosphoric acid--soft drinks
Sodium hydroxide--soap, paper, and rayon
Acids and bases are also used in medicine, disinfectants, titrations, and indicators.
