C1c Smells

We use chemicals that smell nice as perfumes

A family of chemicals that often smell nice is called the esters.

Some esters occur naturally in plants e.g. oranges and lemons

Natural esters can be extracted from the plants that make them and used in

perfumes (we will investigate this further in C4f).

Esters can also be manufactured synthetically by chemists. They are used to

enhance food flavourings e.g. pear drops are made from synthetic esters

How are esters made?

Esters are made by reacting a carboxylic acid and an alcohol together.

Method:

1. Put equal amounts of carboxylic acid and alcohol in a test tube e.g. 10cm3

of each

2. Add 1cm3 of sulfuric acid (as a catalyst) and warm the mixture gently for

5 minutes.

3. Tip the mixture into 100cm3 of sodium carbonate solution to neutralise

the acid.

4. Distil to separate off the ester.

e.g. butanol + ethanoic acid

ethanol + ethanoic acid

ethanol + propanoic acid

+ propanoic acid butyl propanoate

propanol + propyl ethanoate

warm

Higheronly

What properties must a perfume have?

Perfumes have a pleasant smell.

They smell because they stimulate sense cells in the nose

There are 5 physical properties that perfumes must have:

1.

2.

3.

4.

5.

Volatility of Perfumes and Intermolecular Forces

Why do the particles stay together in a liquid?

All particles/molecules are _____________ to each other. Solids - the attractions are very strong and the particles are close

together. Liquids - the attractions are weaker so they can flow over each

other and Gases - the attraction between particles is very weak so they are a

long way apart We call these forces of attraction between particles

_____________________________________

Perfumes need to evaporate at body temperature. This is quite a low

temperature so they must be ___________________.

What does volatile mean?

A liquid that is volatile ____________________ easily i.e. the more volatile a liquid is, the faster it evaporates.

Higher

Summary

1. Perfume molecules (esters) have weak intermolecular forces. 2. Body temperature is enough to break these forces of attraction3. The perfume molecules evaporate from the skin and diffuse to sense cells

in the nose

solid

liquidsolid

gas

Solvents

solute + solvent solution

Water is known as the “universal solvent” because it dissolves many

solids.

All of the cells in your body contain water and the chemical reactions in

those cells all take place in aqueous solution.

But not all solids dissolve in water e.g. nail varnish.

So we have to find alternative solvents

______________, _____________ and _________ can be used as solvents

The more of a solute (solid) you can dissolve in a solvent, the more

soluble that solute is.

e.g.

Solute A Solute B Solute C

10g of solute A

dissolves in 100cm3

of water

5g of solute B

dissolves in 100cm3

of water

0g of solute C

dissolves in 100cm3

of water

Which of these solutes is more soluble? Explain your answer.

Which of these solutes is insoluble in water? Suggest an alternative solvent.

Explain why nail varnish will not dissolve in water

1.

2.

Higher

“Is the testing of cosmetics on animals justified?”

Cosmetics must be tested to ensure that they are __________ to use

e.g. they must not be ___________, react with __________ or

___________ the skin

They cannot be sold unless they have been __________ in some way

Some cosmetics are tested on ______________.

You must be able to explain advantages and disadvantages of testing on

animals. You should develop your own ideas but here are some examples:

Advantages –

Disadvantages –