Cosmetic science
Acids and alkalis
Acids Alkalis
Substances that dissolves in water and form hydrogen ions A base that is soluble in water and releases hydroxide ions.
An acid has a hydrogen ion available to donate in a reaction. A base contains a hydroxide ion
Soluble in water, proton acceptors and neutralize with and acid.
Alkali + acid -> salt + water (neutralisation)
Physical properties Physical properties
Sharp sour taste Feels soapy when in water
Rough feel
Chemical properties Chemical properties
Contains H+ proton soluble base
Proton donor in reaction (proteolytic reaction) changes colour of indicators
Dissolves in water H+ -> H+ +H2O -> H3O+ Neutralize acids: NaOH+HCl
ions ionise to from electrolytes Sodium hydroxide + hydrochloric acid
pH < 7 Turns red litmus blue
Turns blue litmus red
Reacts with metals to produce H and dissolves carbon salts to
release CO2
Organic acids Inorganic acids Effects of alkalis on the skin
(Carboxylic acids) are weak acids Destroys pH of the skin and ▫ Causes dehydration by reacting with skin moisture
and less damaging to the skin. dehydrates by reacting with the ▫ Upsets the skin pH balance which can cause bacterial invasions
Used for peelings and as moisture destroying uppermost ▫ Reacts with skin lipids
electrolytes in electrical cells of the epidermis. ▫ Causes dry skin which feels tight and uncomfortable
treatments. Includes AHAs. ▫ Have no hydrocarbon ▫ Could destroy upper layers of the epidermis
Used to treat acne, ageing and component ▫ Reacts with fats – saponification: hydrolysis of fats which produces
pigmentation. Used as exfoliators. ▫ hydrochloric acid soap.
Proteolytic action on protein sulphuric acid
bridges promotes desquamation. nitric acid Uses
▫ Contains carbon ▫ Strong corrosive medium that ▫ Zinc oxide – sunscreen, antiseptic
▫ General formula R-COOH damages skin and hair. ▫ Calcium hydroxide – depilatory creams
▫ Acetic, butyric, citric, formic, Neutralise with NH4OH ▫ Ammonium hydroxide – hair bleaching
amino, ascorbic and lactic (ammonium hydroxide) ▫ Potassium / sodium hydroxide – cuticle remover
acid
Acetic, butyric, citric, formic, Sulphuric acid NaOH Sodium hydroxide Caustic soda
amino, ascorbic and lactic acid Nitric acid KOH Potassium hydroxide Caustic potash
Ammonium hydroxide Ca(OH)2 Calcium hydroxide Slaked lime
NH4OH Ammonium hydroxide
Strong acids Weak acids Strong bases Weak bases
1. Ionise almost 100% in water 1. Doesn’t easily ionise in water 1. Dissociates completely 1. Dissociates very little
2. Produce high concentration 2. Produces few hydronium ions 2. High hydroxyl ion 2. Low hydroxyl ion
of hydronium ions H3O+ in solution concentration concentration [OH-]
3. Results in low pH 3. pH will be close to 7 3. High pH 3. Lower pH
4. Doesn’t maintain skin pH 4. Maintains skin pH 4. Neutralizes strong acids 4. Can not neutralize a strong
5. Vigorous chemical reaction 5. No vigorous reaction in water acid
in water resulting in heat
Acids Alkalis
o Conduct electricity o Conducts electricity
o Turns blue litmus red o Turns red litmus blue
o Reacts with metals o Feels slippery
o Has a sharp, sour taste o Tastes soapy
o Contains free hydrogen ions o Contains free hydroxyl ions
o Neutralise bases o Neutralises ions
Indicator Indicator
Litmus Red Litmus Blue
Phenolphthalein Colourless Phenolphthalein Pink
Universal indicator Red Universal indicator Blue
Bromothymol-blue Yellow Bromothymol-blue Blue
,pH stands for percentage hydrogen and indicates the number of hydroxide ions in the concentration. The pH scale is from 0-14 where the number
represents the relative acidity of the solution. pH of 7 is neutral meaning the hydronium ion H3O = hydroxide ion OH.
The higher the hydronium content, the lower the pH, the stronger the acid.
The skin has a pH of 4-6. Weak acids maintain the ideal pH of the skin and are the most compatible as they have no negative effects on the acid
mantle or the integrity of the skin. Strong acids and alkalis burn the skin, disrupting the integrity of the skin and enabling infection to occur. Strong
alkalis also disrupt the acid mantle which leads to increased dryness and potential for infection.
Strong acid + weak base -> acidic solution with a pH of 5-6
Weak acid + strong base -> basic salt with a pH of 8
Buffers
A buffer solution resists a change in pH on the addition of an acid or alkali.
The ability to prevent large changes in pH is an important property of most intact biological organisms. Cytoplasmic fluid and blood plasma are highly
effective buffers.
Enzymes in catalytic reactions operate best at a definite pH and buffers control pH within 2,2 pH units.
Neutralisation and salts
Neutral
Substances that have a pH of 7 and do not change the colour of simple indicators or that turns universal indicators green.
Neutral substances can be produced through neutralisation reactions where an acid and base react chemically to form a neutral compound.
Table salt and sugar water are neutral substances.
Neutralisation: Alkali is slowly added to an acid, the hydrogen reacts with the hydroxide and when there are no solitary ions present water is produced.
Hydrogen ion (H+) + Hydroxide ions (OH-) = Water (H2O). Strong acid + strong base = water and pH of 7. Any other ions remaining from the acid and
alkali combine together to form salt – salt formed depends on what acid and base were used.
Salt
A compound that is made up from a metal component and non-metal component and results from a neutralisation reaction. Salts are ionic compounds
that contains positively and negatively charged ions that cancel each other so the salt has no overall charge.
o Products of neutralization. (Acid = alkali)
HCI(acid) + NaOH(alkali) NaCI(salt) + H2O
hydrochloric acid + sodium hydroxide sodium chloride + water
H30+(hydronium ions) + OH-(hydroxyl ions) (reacts completely) 2H20
o Most salts dissolve in water to from solutions
o Metal cation + anion, like Na+Cl
o Crystallization: Ionic compounds where the cations and anions are held together in a crystal lattice by strong electrical forces
o Dissolves easily in solvents with polar molecules like water.
Ways to make salts Reactions
1. Acid and metal ▫ Acid + metal salt + H2
2. Acid and insoluble base ▫ Acid + metal hydroxide salt + H2O (neutralisation)
3. Acid and alkali ▫ Acid + alkali salt + H2O
4. Acid and carbonate ▫ Acid + carbonate salt + Co2 + H2O
5. Precipitation reaction between two salts
Dissociation
Dissociation reaction is a chemical reaction where a compound breaks apart into 2 or more parts.
A polar molecule collides with the ions in the crystal lattice and dislodges an ion through kinetic energy.
Ions are loose in liquid and surrounded by polar molecules which causes the ion to become hydrated (aq – aqueous solution)
▫ NaCI + H2O Na+ (aq) + Cl- (aq)
▫ MgSO4 + H2O Mg2+ (aq) + SO42- (aq)
The solution can then conduct electricity.
Type of acid Type of salt produced
Hydrochloric acid (HCl) Chloride (CL-)
Sulphuric acid (H2SO4) Sulphate (SO4-2)
Nitric acid (HNO3) Nitrate (NO3-)
Phosphoric acid (H2CO3) Phosphate(CO3-2)
, Saponification: soaps and detergents
Where does soap come from: Mount Sapo where the ancient Romans sacrificed animals. Rain would mix animal tallow and wood ash with the
clay soil on the Tiber river bank.
Saponification: the process by which soap is produced. It is the hydrolysis of a fat/ester in the presence of a basic solution to produce an alcohol
and soap. Hydrolysis: process by which water reacts with compounds to break it down and incorporate water into the products that are formed.
The same process is used for desincrusation.
fat alcohol
catalyst
Crude soap is produced in the same way as a mixture of Sodium salts and long-chain fatty acids. Changing compounds can produce:
Made from plant oils – very pure soap (castile soap) NaOH + olive oil in Spain. Marseille soap can have a pH up to 9.
Alcohol added to castile soap – transparent soap
Air beaten into soap – makes soap float
Potassium based alkali (KOH) – liquid or soft soap
Perfumes – masks natural smell
Germicides like triclocarban + triclosan – medicinal soap with antibacterial properties.
o If sodium hydroxide NaOH (caustic soda) is used the product is a solid soap
o If potassium hydroxide KOH is used the product is a liquid soap
Common fatty acids used in soap: stearic, palmitic, oleic, myristic and lauric acid.
How does soap work?
Soap has a hydrocarbon end that makes soap fat-soluble (lipophilic) and salt end that makes the soap water soluble (hydrophilic).
Soap breaks up the triglycerides that makes up a virus and destroys it in the process.
Ways in which soap works:
1. Surfactant: lowers the surface tension of H2O to make it a better solvent and enables it to wet objects easier
2. Emulsifier: breaks up into micelles that dissolves fatty materials and dirt by forming around the fat with the hydrophilic part of the soap on the
outside. The outside surface of the micelles become negatively charged that repels other micelles and causes the fat droplet to be dispersed in
water. Soap micelles are emulsifying agents that result in a stable emulsion of water, oil and dirt that is removed easily from the surface. The
molecules do not dissolve in the water but is rather dispersed in the water.
Problem is that soap can precipitate scum with hard water which contains calcium and magnesium ions
Detergents: soaps that are synthetically prepared and are obtained from straight-chain primary alcohols instead of fats and varies in chemical
structure. Detergents dissolve oily dirt by forming emulsion. Dove is an example of a solid detergent.
Detergents have the advantage that hey do not precipitate calcium and magnesium ions in hard water and thus does not leave scum.
Both soaps and detergents have large non-polar hydrocarbon ends that is oil-soluble and a polar end that is water soluble.
Surfactants: (wetting agents): surface active agents. Reduces surface tension of water. Negative molecule.
1. Anionic surfactant – used in cosmetic emulsifiers as it is cheap and stable. Ex. Sodium laurel sulphate.
Domestic detergents, like detergent powders and liquids and toilet soaps. Foams excessively.
2. Cationic surfactant – poorly tolerated by most skins. Ex. Ammonium laurel sulphate
Strong anti-bacterial action and used in hospitals and skincare clinics. Anti-static in hair rinses and fabric softeners.
3. Non-ionic surfactant – used In skin-care emulsions for safety and low reactivity. Ex. Cetyl alcohol and oleyl alcohol.
Does not ionize in water but has hydrophobic and hydrophilic properties and is able to emulsify fats in water.
Does not foam and contain additives like foam stabilizers and bleaches.
4. Amphoteric surfactant
Positively or negatively charged depending on the pH of the water. Used in cosmetics for mildness like in Dove shampoos and lotions
Surfactant functions:
▫ Detergents for cleansing
▫ Wetting agents in perms
▫ Emulsifier for creams and lotions
▫ Solubilizers for perfumes and flavours
▫ Conditioning agent in skin products
Resting membrane potential:
Difference in the charge on the inside (-)
and the outside (+) of the cell membrane.
Usually 60-90 millivolts.
Acids and alkalis
Acids Alkalis
Substances that dissolves in water and form hydrogen ions A base that is soluble in water and releases hydroxide ions.
An acid has a hydrogen ion available to donate in a reaction. A base contains a hydroxide ion
Soluble in water, proton acceptors and neutralize with and acid.
Alkali + acid -> salt + water (neutralisation)
Physical properties Physical properties
Sharp sour taste Feels soapy when in water
Rough feel
Chemical properties Chemical properties
Contains H+ proton soluble base
Proton donor in reaction (proteolytic reaction) changes colour of indicators
Dissolves in water H+ -> H+ +H2O -> H3O+ Neutralize acids: NaOH+HCl
ions ionise to from electrolytes Sodium hydroxide + hydrochloric acid
pH < 7 Turns red litmus blue
Turns blue litmus red
Reacts with metals to produce H and dissolves carbon salts to
release CO2
Organic acids Inorganic acids Effects of alkalis on the skin
(Carboxylic acids) are weak acids Destroys pH of the skin and ▫ Causes dehydration by reacting with skin moisture
and less damaging to the skin. dehydrates by reacting with the ▫ Upsets the skin pH balance which can cause bacterial invasions
Used for peelings and as moisture destroying uppermost ▫ Reacts with skin lipids
electrolytes in electrical cells of the epidermis. ▫ Causes dry skin which feels tight and uncomfortable
treatments. Includes AHAs. ▫ Have no hydrocarbon ▫ Could destroy upper layers of the epidermis
Used to treat acne, ageing and component ▫ Reacts with fats – saponification: hydrolysis of fats which produces
pigmentation. Used as exfoliators. ▫ hydrochloric acid soap.
Proteolytic action on protein sulphuric acid
bridges promotes desquamation. nitric acid Uses
▫ Contains carbon ▫ Strong corrosive medium that ▫ Zinc oxide – sunscreen, antiseptic
▫ General formula R-COOH damages skin and hair. ▫ Calcium hydroxide – depilatory creams
▫ Acetic, butyric, citric, formic, Neutralise with NH4OH ▫ Ammonium hydroxide – hair bleaching
amino, ascorbic and lactic (ammonium hydroxide) ▫ Potassium / sodium hydroxide – cuticle remover
acid
Acetic, butyric, citric, formic, Sulphuric acid NaOH Sodium hydroxide Caustic soda
amino, ascorbic and lactic acid Nitric acid KOH Potassium hydroxide Caustic potash
Ammonium hydroxide Ca(OH)2 Calcium hydroxide Slaked lime
NH4OH Ammonium hydroxide
Strong acids Weak acids Strong bases Weak bases
1. Ionise almost 100% in water 1. Doesn’t easily ionise in water 1. Dissociates completely 1. Dissociates very little
2. Produce high concentration 2. Produces few hydronium ions 2. High hydroxyl ion 2. Low hydroxyl ion
of hydronium ions H3O+ in solution concentration concentration [OH-]
3. Results in low pH 3. pH will be close to 7 3. High pH 3. Lower pH
4. Doesn’t maintain skin pH 4. Maintains skin pH 4. Neutralizes strong acids 4. Can not neutralize a strong
5. Vigorous chemical reaction 5. No vigorous reaction in water acid
in water resulting in heat
Acids Alkalis
o Conduct electricity o Conducts electricity
o Turns blue litmus red o Turns red litmus blue
o Reacts with metals o Feels slippery
o Has a sharp, sour taste o Tastes soapy
o Contains free hydrogen ions o Contains free hydroxyl ions
o Neutralise bases o Neutralises ions
Indicator Indicator
Litmus Red Litmus Blue
Phenolphthalein Colourless Phenolphthalein Pink
Universal indicator Red Universal indicator Blue
Bromothymol-blue Yellow Bromothymol-blue Blue
,pH stands for percentage hydrogen and indicates the number of hydroxide ions in the concentration. The pH scale is from 0-14 where the number
represents the relative acidity of the solution. pH of 7 is neutral meaning the hydronium ion H3O = hydroxide ion OH.
The higher the hydronium content, the lower the pH, the stronger the acid.
The skin has a pH of 4-6. Weak acids maintain the ideal pH of the skin and are the most compatible as they have no negative effects on the acid
mantle or the integrity of the skin. Strong acids and alkalis burn the skin, disrupting the integrity of the skin and enabling infection to occur. Strong
alkalis also disrupt the acid mantle which leads to increased dryness and potential for infection.
Strong acid + weak base -> acidic solution with a pH of 5-6
Weak acid + strong base -> basic salt with a pH of 8
Buffers
A buffer solution resists a change in pH on the addition of an acid or alkali.
The ability to prevent large changes in pH is an important property of most intact biological organisms. Cytoplasmic fluid and blood plasma are highly
effective buffers.
Enzymes in catalytic reactions operate best at a definite pH and buffers control pH within 2,2 pH units.
Neutralisation and salts
Neutral
Substances that have a pH of 7 and do not change the colour of simple indicators or that turns universal indicators green.
Neutral substances can be produced through neutralisation reactions where an acid and base react chemically to form a neutral compound.
Table salt and sugar water are neutral substances.
Neutralisation: Alkali is slowly added to an acid, the hydrogen reacts with the hydroxide and when there are no solitary ions present water is produced.
Hydrogen ion (H+) + Hydroxide ions (OH-) = Water (H2O). Strong acid + strong base = water and pH of 7. Any other ions remaining from the acid and
alkali combine together to form salt – salt formed depends on what acid and base were used.
Salt
A compound that is made up from a metal component and non-metal component and results from a neutralisation reaction. Salts are ionic compounds
that contains positively and negatively charged ions that cancel each other so the salt has no overall charge.
o Products of neutralization. (Acid = alkali)
HCI(acid) + NaOH(alkali) NaCI(salt) + H2O
hydrochloric acid + sodium hydroxide sodium chloride + water
H30+(hydronium ions) + OH-(hydroxyl ions) (reacts completely) 2H20
o Most salts dissolve in water to from solutions
o Metal cation + anion, like Na+Cl
o Crystallization: Ionic compounds where the cations and anions are held together in a crystal lattice by strong electrical forces
o Dissolves easily in solvents with polar molecules like water.
Ways to make salts Reactions
1. Acid and metal ▫ Acid + metal salt + H2
2. Acid and insoluble base ▫ Acid + metal hydroxide salt + H2O (neutralisation)
3. Acid and alkali ▫ Acid + alkali salt + H2O
4. Acid and carbonate ▫ Acid + carbonate salt + Co2 + H2O
5. Precipitation reaction between two salts
Dissociation
Dissociation reaction is a chemical reaction where a compound breaks apart into 2 or more parts.
A polar molecule collides with the ions in the crystal lattice and dislodges an ion through kinetic energy.
Ions are loose in liquid and surrounded by polar molecules which causes the ion to become hydrated (aq – aqueous solution)
▫ NaCI + H2O Na+ (aq) + Cl- (aq)
▫ MgSO4 + H2O Mg2+ (aq) + SO42- (aq)
The solution can then conduct electricity.
Type of acid Type of salt produced
Hydrochloric acid (HCl) Chloride (CL-)
Sulphuric acid (H2SO4) Sulphate (SO4-2)
Nitric acid (HNO3) Nitrate (NO3-)
Phosphoric acid (H2CO3) Phosphate(CO3-2)
, Saponification: soaps and detergents
Where does soap come from: Mount Sapo where the ancient Romans sacrificed animals. Rain would mix animal tallow and wood ash with the
clay soil on the Tiber river bank.
Saponification: the process by which soap is produced. It is the hydrolysis of a fat/ester in the presence of a basic solution to produce an alcohol
and soap. Hydrolysis: process by which water reacts with compounds to break it down and incorporate water into the products that are formed.
The same process is used for desincrusation.
fat alcohol
catalyst
Crude soap is produced in the same way as a mixture of Sodium salts and long-chain fatty acids. Changing compounds can produce:
Made from plant oils – very pure soap (castile soap) NaOH + olive oil in Spain. Marseille soap can have a pH up to 9.
Alcohol added to castile soap – transparent soap
Air beaten into soap – makes soap float
Potassium based alkali (KOH) – liquid or soft soap
Perfumes – masks natural smell
Germicides like triclocarban + triclosan – medicinal soap with antibacterial properties.
o If sodium hydroxide NaOH (caustic soda) is used the product is a solid soap
o If potassium hydroxide KOH is used the product is a liquid soap
Common fatty acids used in soap: stearic, palmitic, oleic, myristic and lauric acid.
How does soap work?
Soap has a hydrocarbon end that makes soap fat-soluble (lipophilic) and salt end that makes the soap water soluble (hydrophilic).
Soap breaks up the triglycerides that makes up a virus and destroys it in the process.
Ways in which soap works:
1. Surfactant: lowers the surface tension of H2O to make it a better solvent and enables it to wet objects easier
2. Emulsifier: breaks up into micelles that dissolves fatty materials and dirt by forming around the fat with the hydrophilic part of the soap on the
outside. The outside surface of the micelles become negatively charged that repels other micelles and causes the fat droplet to be dispersed in
water. Soap micelles are emulsifying agents that result in a stable emulsion of water, oil and dirt that is removed easily from the surface. The
molecules do not dissolve in the water but is rather dispersed in the water.
Problem is that soap can precipitate scum with hard water which contains calcium and magnesium ions
Detergents: soaps that are synthetically prepared and are obtained from straight-chain primary alcohols instead of fats and varies in chemical
structure. Detergents dissolve oily dirt by forming emulsion. Dove is an example of a solid detergent.
Detergents have the advantage that hey do not precipitate calcium and magnesium ions in hard water and thus does not leave scum.
Both soaps and detergents have large non-polar hydrocarbon ends that is oil-soluble and a polar end that is water soluble.
Surfactants: (wetting agents): surface active agents. Reduces surface tension of water. Negative molecule.
1. Anionic surfactant – used in cosmetic emulsifiers as it is cheap and stable. Ex. Sodium laurel sulphate.
Domestic detergents, like detergent powders and liquids and toilet soaps. Foams excessively.
2. Cationic surfactant – poorly tolerated by most skins. Ex. Ammonium laurel sulphate
Strong anti-bacterial action and used in hospitals and skincare clinics. Anti-static in hair rinses and fabric softeners.
3. Non-ionic surfactant – used In skin-care emulsions for safety and low reactivity. Ex. Cetyl alcohol and oleyl alcohol.
Does not ionize in water but has hydrophobic and hydrophilic properties and is able to emulsify fats in water.
Does not foam and contain additives like foam stabilizers and bleaches.
4. Amphoteric surfactant
Positively or negatively charged depending on the pH of the water. Used in cosmetics for mildness like in Dove shampoos and lotions
Surfactant functions:
▫ Detergents for cleansing
▫ Wetting agents in perms
▫ Emulsifier for creams and lotions
▫ Solubilizers for perfumes and flavours
▫ Conditioning agent in skin products
Resting membrane potential:
Difference in the charge on the inside (-)
and the outside (+) of the cell membrane.
Usually 60-90 millivolts.
