3.4 Basics of Chemistry & pH Scale

3.4 Basics of Chemistry & pH Scale

Quick Summary: Cosmetology is rooted in chemical science. Every hair coloring, perming, relaxing, and skin conditioning service relies on chemical reactions. State board examinations test candidate knowledge of organic vs. inorganic chemistry, physical vs. chemical changes, cosmetic formulation types (solutions, suspensions, emulsions), surfactant physics, and logarithmic pH scale mechanics.

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Organic vs. Inorganic Chemistry

All matter is classified into two primary branches of chemistry:

1. Organic Chemistry

• The study of substances that contain the element carbon.
• All organic substances are capable of burning or are flammable.
• Cosmetology Examples: Haircolors, shampoos, conditioners, synthetic hair fibers, styling gels, plant oils, and skin creams.

2. Inorganic Chemistry

• The study of substances that do not contain carbon (and may contain hydrogen).
• Inorganic substances are non-flammable and were never alive.
• Cosmetology Examples: Pure water, minerals, hydrogen peroxide ($H_2O_2$), ammonium thioglycolate ingredients, metallic salts, and air.

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States of Matter & Changes of Matter

Matter exists in three distinct physical states: solid (fixed shape and volume), liquid (fixed volume, variable shape), and gas (variable volume and shape).

Physical Changes vs. Chemical Changes

Cosmetology procedures fall cleanly into physical or chemical transformations:

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Chemistry of Mixtures: Solutions, Suspensions & Emulsions

Cosmetology products are physical mixtures of two or more substances:

1. Solutions:

   • A stable, uniform mixture of two or more soluble substances.
   • Solute: The substance that is dissolved (e.g., salt or powder).
   • Solvent: The liquid medium that dissolves the solute (water is the universal solvent).
   • Solutions do not separate upon standing and are typically transparent (e.g., hydrogen peroxide developer).

2. Suspensions:

   • An unstable physical mixture of undissolved solid particles distributed throughout a liquid.
   • Particles are visible and will settle to the bottom over time, requiring shaking before use (e.g., glitter nail polish, calamine lotion).

3. Emulsions:

   • An unstable physical mixture of two or more immiscible liquids (liquids that do not normally mix, like oil and water) held together by an emulsifier called a surfactant.
   • Emulsions separate very slowly over time (e.g., hand lotions, cold creams, hair conditioners).

Surfactant Chemistry (Surface Active Agents)

Surfactants allow immiscible liquids to emulsify. A surfactant molecule has a dual-end structure:

• Hydrophilic Head: Water-loving, polar end that dissolves in water.
• Lipophilic Tail: Oil-loving, non-polar end that dissolves in oil.

In an Oil-in-Water (O/W) emulsion, oil droplets are emulsified inside water (e.g., most hair conditioners). In a Water-in-Oil (W/O) emulsion, water droplets are emulsified inside oil (e.g., heavy night creams, cleansing creams).

          [ SURFACTANT MOLECULE DYNAMICS ]

      Hydrophilic Head        Lipophilic Tail
       (Water-Loving)          (Oil-Loving)
           ( O )=========================
             |                      |
      Attaches to Water      Attaches to Oil

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The pH Scale & Hair / Skin Acid Mantle

pH stands for Potential Hydrogen, representing the relative concentration of hydrogen ions ($H^+$) versus hydroxyl ions ($OH^-$) in a water-based solution. Pure water has equal amounts of $H^+$ and $OH^-$ ions and is neutral at pH 7.0.

The Logarithmic pH Scale (0 to 14)

• The pH scale ranges from 0 to 14.
• Acidic Range (0 to 6.9): Contains higher concentration of $H^+$ ions.
• Neutral Point (7.0): Equal balance of $H^+$ and $OH^-$ ions.
• Alkaline Range (7.1 to 14): Contains higher concentration of $OH^-$ ions.
• Logarithmic Scale: Each whole number change represents a 10-fold (10x) change in ion concentration.
  • Example: pH 8 is 10 times more alkaline than pH 7.
  • Example: pH 9 is 100 times ($10 \times 10$) more alkaline than pH 7.

                          [ THE pH SCALE ]

  0 ----- 4.5 - 5.5 ----- 7.0 ------------------------ 14
  [  ACIDIC RANGE  ]     [NEUTRAL]     [  ALKALINE RANGE  ]
        ^                    ^
   Natural Skin/Hair     Pure Water
      Acid Mantle

Chemical Action of pH on Hair Cuticle

• Natural Acid Mantle: Hair and skin possess a natural protective barrier (sweat + sebum) with an acidic pH of 4.5 to 5.5.
• Alkaline Products (pH > 7.0): Open, swell, and lift the hair cuticle scale layer. Required for perm processing, hair relaxers, and oxidative color penetration.
• Acidic Products (pH < 7.0): Contract, harden, tighten, and close the hair cuticle scale layer. Used in post-chemical neutralizing rinses to seal moisture and lock in color.

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Cosmetology Chemical Product pH Matrix