A short intro to :

Acids & Bases

This page serves to cover some basic information on acids, bases, and one of their uses in hair application through the lens of a tenth grader. The page is loaded with information so a drink or two is recommended.

Physical properties

Some physical properties of acids and bases, including taste, smell, texture, and color change in the litmus test, are different. These properties can be utilized to differentiate between the two types.

Properties :

Taste = Acids - sour, Bases - bitter
Smell = Acids - burns nose, Bases - no smell
Texture = Acids - Rough, Bases - slippery
Litmus test = Acids - Blue > Red, Bases - Red > Blue

Definitions

Now that we've glossed over identification of acids and bases, lets dive into what the specifics of what they actually are. These are the 3 main definitions for acids and bases.

Arrhenius :

Acids = H+ in H2O, Bases = OH- in H2O

Bronsted - Lowry :

Acids = H+ donor, Bases = H+ acceptor

Lewis :

Acids = accepts e- pair, Bases = e- pair donator

Strength

Acids and bases have different strengths. Some acids are weak whilst some are strong; the same principle applies to bases. Strength is measured by how well a specific substance dissociates into H+ (acids) or OH- (bases) in an aqueous solution.

Examples

NaOH (aq) Na+ (aq) + OH- (aq)
HCl (aq) H+ (aq) + Cl- (aq)

Here, both NaOH and HCl dissociate completely, as indicated by their arrows both pointing towards the right. This means that they are both incredibly strong because they produce more H+/OH- than other weaker acids/bases in an aqueous solution. (Don't forget that H+ and OH- quantities define acids and bases as per Arrhenius' definition.)

Hair relaxers

In this day and age, hair alterations are growing more and more prevalent, hair relaxers being one of them. To understand how they work, an understanding of hair is a prerequisite.

Hair :

One of the most important components of hair is Keratin, a protein made largely from the amino acid cystine. Cystine itself is acidic, which contributes to the acidity of hair (pH 4-5).

Hair relaxers :

Hair relaxers are a type of lotion or cream which make hair easier to straighten and manage. They reduce curling by reducing cystine to cysteine. This does controlled damage to hair, allowing its structure to change. The substance used in hair relaxers are often basic (such as NaOH) to counteract the acidic nature of hair.

After all those dreadful lines and paragraphs on acids and bases, let's see if you've gained some understanding on the topic.

Assume you have acquired two acids, HX & HY. You are told one is weak and one is strong, and you need to identify which is which for an experiment. Luckily, you are provided a graph detailing equilibrium concentrations (mol/L) of both acids and their products when ionized in water.

The results are :

HX (negligible) + H2O ---> X- (1*10^-2) + H3O+ (1*10^-2)
HY (9.97*10^-3) + H2O <---> Y- (3.16*10^-5) + H3O+ (3.16*10^-5)

Which of the two acids is the stronger one?

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