Fragrances and Skin care Flashcards
Why are the alkanes used as fuels?
due to the ease with which they combust
What do alkanes take part in?
substitution reactions with the halogens in the presence of high energy UV light
What does the substitution reaction between an alkane and a halogen occur via?
a chain reaction involving initiation, propagation and termination
What is the equation for the substitution reaction between methane and chlorine?
CH4 + Cl2 > CH3Cl + HCl
remember UV light at arrow
Using the reaction between methane and chlorine describe what happens during initiation?
Cl - Cl > Cl. + Cl.
The UV light provides energy to break the bond between the chlorine atoms into chlorine radicals.
What is a radical?
a highly reactive atom or group of atoms with an unpaired electron.
Using the reaction between methane and chlorine describe what happens during propagation?
CH3-H + Cl. > CH3. + HCl
CH3. + Cl2 > CH3-Cl + Cl.
In each propagation step, one radical enters the reaction and another is generated. These steps propagate the cahin reaction
Using the reaction between methane and chlorine describe what happens during termination?
CH3. + Cl. > CH3-Cl
CH3. + CH3. > CH3CH3
Cl. + Cl. > Cl2
During the reaction, the concentration of radicals increases and due to this, more collisions between radicals occur. This results in producing stable molecules. As a result the chain reaction is brought to an end.
What is ultraviolet radiation?
a high energy form of light, present in sunlight
What can exposure to UV trials result in?
molecules gaining sufficient energy for bonds to be broken. This is the process responsible for sunburn and also contributes to ageing skin
To combat the effects of UV light, what do sunblock products contain?
chemicals which reflect the UV light. In this way the skin is protected.
What chemicals do many cosmetic products such as hand creams contain? (2)
free radical scavengers (often vitamin and minerals)
What do free radical scavengers do?
react with radicals to form stable molecules. As a result, this stops the free radical chain reactions that would damage the skin
What are free radical scavengers also added to?
food products and to plastics to prevent the formation of rancid products
Give an example of a free radical scavenger?
vitamin C
