Chapter 1: Lifestyle Chemistry Flashcards
1
Q
What is a suspension?
A
When two liquids get put together and they separate from each other forming layers. An example is oil and water
2
Q
What is a solvent?
A
A substance that dissolves something else. An example is water or alcohol
3
Q
What is a colloid?
A
A colloid is a homogeneous, noncrystalline substance consisting of large molecules or ultramicroscopic particles of one substance dispersed through a second substance
4
Q
What is a solution?
A
A solution is a substance that disolves in a solvent (typically water or alcohol)
5
Q
What is a property?
A
Characteristic of a substance
6
Q
Physical properties
A
Can be found by studying the substance itself rather than its reactions
E.g. Hardness, malleability, density
7
Q
Chemical properties
A
Describes how a substance reacts
E.g. Whether it reacts with water, oxygen or acids and if it decomposes when heated
8
Q
Properties of solutions
A
- contains at least one substance dissolved in another
- uniform (homogenous) throughout - can’t see individual substances contained in it
E.g. Perfumes, food colouring and petrol
9
Q
Properties of suspensions
A
- contain large particles that aren’t dissolved in a solvent
- mix uniformly together if the product is shaken
- overtime it settles out or forms layers
- non-uniform (heterogenous) mixtures particles are often large enough to see
- force of attraction between the solvent particles and the large particles are not strong enough and overtime gets pulled down by gravity
- advantage is they form a stable mixture that lasts well
E.g. Paint, cough mixtures and salad dressings
10
Q
Properties of colloids
A
- also contains particles but remain suspended for long periods of time
- contains properties that are halfway between suspensions and sollutions
- has particles bigger than solutions but smaller than suspensions
- not completely homogenous or heterogenous
- particles and/or medium may be solid, liquids or bubbles of gas
- advantages are that it allows a substance to be delivered to that specific part of the body and it is in a stable form ready to use
E.g. Aerosols, cement, foam and paint
11
Q
Tyndall effect
A
Beam of light that is visable / shatters when it passes through a colloid or suspension but not a solution
12
Q
Oil
A
- non-polar molecule
- molecule is neutral
- non-polar molecules dissolve in other non-polar molecules
13
Q
Water (and lemon juice, vinegar)
A
- polar molecule
- one end is slightly negative
- other end is slightly positive
- polar molecules dissolve in other polar molecules
14
Q
Beaten or whisked eggs
A
- leaves a colloid
- clear separate layer in the egg (see it go light, dark and frothy)
- egg white dissolves leaving the egg yolk behind
15
Q
Salad dressing (oil and vinegar)
A
- makes a suspension
- can see the substances separate
- can see the oil spots on top of vinegar
16
Q
Mayonnaise
A
- made out of egg yolk, vinegar and oil
- makes a colloid
- creates a mixture together that isn’t spotty/blotchy
- smooth and isn’t 100% dissolved meaning it can’t be a solution
- one liquid layer meaning it can’t be a suspension
- egg is used as an emulsifier
17
Q
Oil-in-water
A
Contains oil particles dispersed in a water medium
- lecithin can be used to emulsify an oil-in-water mixture
E.g.s:
- aerosols
- cement
- foam
- paint
- milk
18
Q
Water-in-oil
A
Contains water particles dispersed in an oil medium
- cholesterol (in egg yolk) can be used to emulsify a water-in-oil mixture
E.g.s:
- mayonnaise
- margarine
19
Q
Gas-in-liquid (foams)
A
Most widely used emulsifiers in foods such as glyceryl monostearate (GMS) which is used in:
- margarine
- salad dressings
- ice cream
20
Q
What is surface tension
A
The tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid (due to opposite attraction) which tends to minimise surface area
21
Q
Force of surface tension
A
- forces of attraction between water molecules (due to the positive and negative ends)
- acts over short distances
- very weak
- continually breaking and reforming
- forces hold the molecules in their liquid state
- acts equally in all directions of the molecules of the liquid
- at the surface the forces don’t act equally on the molecules
- surface layer molecules are strongly related with the molecules in the layer underneath and not the molecules in the air above
22
Q
Cohesion
A
Force that holds together like or unlike atoms, ions or molecules of a single body
23
Q
Adhesion
A
Force that holds together two separate bodies together (or to stick one body to another)
24
Q
The shape of liquid drops
A
- makes a spherical shape
- detergent reduces surface tension
- unbalanced attractive forces result in molecules being pulled inwards and as few molecules as possible remaining for the shortest time possible at the surface
25
Formation of menisci
- depends on the width of the test tube
- if it is a wide test tube - further distance, flat and can't overcome gravity
- if it is a thinner test tube - closer distance, curved as it pushes itself together
26
Ability of some insects to walk on water
- water has a high degree of surface tension
- their legs are shaped to distribute their weight over a larger surface area so that the insects weight is better balance
- strong surface tension of the water can then hold the insects weight and prevent the bug from sinking due to gravity
- due to the surface tension, insects can run on water without sinking
27
What is a surfactant
Chemical that works at the surface of a substance to reduce the surface tension between liquids, or between a liquid and a solid. This improves the ability of a substance to wet, mix with or spread over another substance
28
Properties of surfactants
- detergent reduces surface tension of water
- works at the boundary layer between two substances
- molecule has 2 parts (hydrophobic and hydrophyllic)
- when added to water, the tails try to get away from the water molecules by moving to the water surface with the tails pointing out of the water or forming tight balls called micelles
- when surfactant molecules are spread over the water surface, the forces of attraction between water molecules are reduced
- if a surfactant, oil and water are stirred, the surfactant molecules are drawn to the surfaces between the oil and water
- tails attach to the oil and heads attach to the water
29
Hydrophobic tail
- chemically similar to oil
| - part will dissolve in oil
30
Hydrophilic head
- chemically similar to water
| - part will dissolve in water
31
Effects of soap, skin cleansers and shampoos on the solubility of oils
- oil won't dissolve in water
- water won't dissolve in oil
- therefore they are immiscible (don't form a solution)
- if shaken together, they form a suspension and after a short period of time they will separate into layers
- more or less permanent mixture of oil and water can be made using a surfactant
- acts at the boundaries of two substances
- soaps, skin cleansers and shampoos all contain surfactants
32
Effects of soap, skin cleansers and shampoos on the solubility of oil (continued)
- oil won't dissolve in water but they are "glued" together by surfactant molecules
- continued stirring produces smaller and smaller oil droplets
- surfactant molecules coat each droplet
- heads because of their slightly positive nature tend to repel each other and for this reason the oil droplets remain suspended
33
List for soaps, detergents and oils
1. Oil is attached to the surface
2. The cleaning action is due to the surfactants attaching onto the oil and dirt embedded in various surfaces that need to be cleaned
3. As the mixture is stirred, the water molecules pull the surfactants and their attached oil and dirt out of whatever they are attached to
4. The oil-dirt droplets remain suspended in the water, when the water is drained away the oil and dirt are removed as well, this leaves the surface (material) clean
34
What is an emulsion
Type of colloid containing two liquids
35
Relationship between the properties of an emulsion and the types of molecules present
- droplets of one liquid (dispersed phase) are spread evenly throughout another immiscible liquid (dispersion medium)
- related to the type of molecules present
- two liquids that don't mix are called phases
- an emulsifier gets added to these phases and mixes them together and reduces the differences in surface tension
- must have small particles because if they are too heavy, they settle into layers
- has a strong affinity (bond) with either the liquid or the oil phase
36
HLB scale (hydrophilic-lipophilic balance)
- given a rate from 1-20
- emulsifiers with a rate from 3-6 prefer to mix with the oil phase and make water-in-oil emulsions
- emulsifiers with a rate from 7-14 give emulsions of oil-in-water
- name of the emulsion tells you the phase the emulsifier had the greater affinity for (an oil-in-water emulsion had an emulsifier with an affinity of water)
37
HLB of 1-3
Antifoaming agents - used to reduce the surface tension of a solution or emulsion, thus preventing formation of foam; or is added to break a foam already formed
38
HLB of 3-6
Water-in-oil emulsions
39
HLB of 7-9
Wetting agents - used to make products such as agricultural sprays adhere to hydrophobic waxy leaves
40
HLB of 7-14
Oil-in-water emulsions
41
HLB of 13-16
Detergents
42
HLB of 17-20
Solubilisers - used to dissolve small amounts of oil (usually fragrances) in water-based products, such as skin toners and floral waters
43
What is an emulsifying agent
Substance that makes a suspension become an emulsion- it breaks the suspended particles into smaller sizes so they stay suspended. Acts as a surfactant as it allows substances to mix together when they would not normally do so
44
Purposes of an emulsifying agent in a range of consumer cleaning products
Water and oil don't normally mix and when you are cleaning something, you are trying to make them mix so an emulsifying agent needs to be added as it works with both the hydrophobic tail and hydrophilic head e.g dishwashing liquid
45
Anionic surfactants
Property:
Highly sudsing. Excellent cleaning properties. They are not very good at cleaning plastics
Structure:
Negatively charged head and hydrocarbon tail
Use:
Laundry detergents; dishwashing liquids; hair shampoos; adding dyes to textiles; in engine lubricants; keep chemicals suspended in chemicals used in agriculture
46
Cationic surfactants
Property:
Breaks cell walls of bacteria (due to ammonium in the head). They form a smooth layer on the fabric or hair surface when the positive end of the molecule is attracted to the negatively charged fibres in fabric or hair which reduces static and tangling
Structure:
Positively charged head and hydrocarbon tail
Use:
Disinfectants; antiseptic soaps; mouthwashes; nappy washes; antistatic agents; flocculants in sewage treatments
