Understanding SoapUnderstanding Soap

When was soap first used?

When was soap first used?

Soaps have been excavated in clay cylinders that date back to 2800 B.C. 

An ancient Egyptian scroll dated to 1500 B.C. describes a soap recipe

Soaps have been excavated in clay cylinders that date back to 2800 B.C. 

An ancient Egyptian scroll dated to 1500 B.C. describes a soap recipe

People learned that fats would react with ingredients in fire ashes to produce soap

People learned that fats would react with ingredients in fire ashes to produce soap

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One common soap was made by mixing ashes with animal fat (also called tallow)

https://www.youtube.com/watch?v=t0EgtWv6kBA

One common soap was made by mixing ashes with animal fat (also called tallow)

https://www.youtube.com/watch?v=t0EgtWv6kBA

ASHES FAT SOAP

How is soap made today?How is soap made today?

Today, soaps are made from fats and oils that react with lye (sodium hydroxide) instead of ashes.

Chemical Reaction: Fat or Oil + NaOH Soap + Glycerol

Because soap is made by this reaction, the reaction is sometimes called “saponification”

https://www.youtube.com/watch?v=Fuu1ZCg5byg

Today, soaps are made from fats and oils that react with lye (sodium hydroxide) instead of ashes.

Chemical Reaction: Fat or Oil + NaOH Soap + Glycerol

Because soap is made by this reaction, the reaction is sometimes called “saponification”

https://www.youtube.com/watch?v=Fuu1ZCg5byg

Back to Science 10…Back to Science 10… Recall that when you mix an acid and a

base, a salt results:

Acid + Base Salt

This is actually how soap is made. Oils and fats (also called

triglycerides) are acids Sodium hydroxide (lye) is written

NaOH and is a base Soap is a salt that results when the

two react

Interestingly, we use soap to cleanse grease and oils from our skin, but soap is made from grease & oils!

This is a reminder that when a chemical reaction occurs, completely different substances are created!

Recall that when you mix an acid and a base, a salt results:

Acid + Base Salt

This is actually how soap is made. Oils and fats (also called

triglycerides) are acids Sodium hydroxide (lye) is written

NaOH and is a base Soap is a salt that results when the

two react

Interestingly, we use soap to cleanse grease and oils from our skin, but soap is made from grease & oils!

This is a reminder that when a chemical reaction occurs, completely different substances are created!

How is soap made today?How is soap made today? Saponification Reaction:

Fat or Oil + NaOH Soap + Glycerol

Different fats or oils are used in the saponification reaction, and this produces soap with different qualities

Examples of fats used to make soap:

Saponification Reaction:

Fat or Oil + NaOH Soap + Glycerol

Different fats or oils are used in the saponification reaction, and this produces soap with different qualities

Examples of fats used to make soap:

How is soap made today?How is soap made today?

Tallow is beef fat that has been purified (“rendered”)

https://www.youtube.com/watch?v=DKOVoAsIKhY

Lard is rendered pork fat

Solid fats like coconut oil, palm oil, tallow or lard form bars of soap that stay hard and resist dissolving in the water left in the soap dish.

Tallow is beef fat that has been purified (“rendered”)

https://www.youtube.com/watch?v=DKOVoAsIKhY

Lard is rendered pork fat

Solid fats like coconut oil, palm oil, tallow or lard form bars of soap that stay hard and resist dissolving in the water left in the soap dish.

The Structure of SoapThe Structure of Soap

• You start with a fat molecule, which contains:

• H – hydrogen

• C – carbon

• O – oxygen

• Fat molecules are also called “triglycerides”. You will notice three identical arms of the molecule, which is where the “tri” comes from

• The various fats & oils that can be used in soapmaking all have this basic structure.

• You start with a fat molecule, which contains:

• H – hydrogen

• C – carbon

• O – oxygen

• Fat molecules are also called “triglycerides”. You will notice three identical arms of the molecule, which is where the “tri” comes from

• The various fats & oils that can be used in soapmaking all have this basic structure.

A fat molecule (a.k.a. a triglyceride)

Build your own fat molecule… Then we’ll see what happens to it in the saponification reaction!

Saponification Reaction:

ACID BASE SALT

Fat or Oil + NaOH Soap + Glycerol (Triglyceride) (lye or

sodium hydroxide)

CH2 – OH

CH – OH

CH2 – OH

+ 3 NaOH

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