Flashcards in C1 9-16 Deck (36):
Forces and cross links
The polymer molecules in many plastics are attracted to each other only by weak intermolecular forces. These are easily overcome, so such plastics have low melting points. They are also easily stretched because the molecules can slide past one another.
The polymer molecules in other plastics have strong covalent bonds between them. These cross-links stop the molecules moving apart or past one another. Such plastics have high melting points. They are rigid and cannot be easily stretched.
Why are many polymers not biodegradable?
They can bit be decomposed by bacterial action.
Why are plastics burnt?
Waste plastic can be burnt to release heat energy. This can be used to generate electricity or to heat buildings. The plastic must be burnt at a high temperature to stop toxic gases being made. Unless the heat energy released is used, disposal by burning is a waste of a valuable resource.
What is the problem with recycling polymers?
It must be sorted into separate types of polymer by hand which is difficult and expensive
How do biodegradable polymers work?
In one type, starch is added to poly(ethene) or other polymers during manufacture. Once the polymer gets wet, bacteria break down the starch, causing the plastic item to crumble into very small pieces. Other new polymers dissolve in water. For example, dishwasher detergent tablets are wrapped in a plastic that dissolves once it gets wet in the dishwasher.
How do you know a chemical change has occurred?
• a new substance is made
• the change is irreversible
• an energy change happens.
What happens when you cook an egg?
The texture and appearance of egg white, egg yolk, and meat change when they are cooked. This is because their protein molecules change shape when heated. Once a protein has been denatured, it cannot be changed back again, so the process is irreversible.
What happens when you cook a potato?
When a potato is cooked, the cell walls break. This makes the potato lose its rigid structure and become softer. It also releases the starch grains. These absorb water and swell up. Cooked potato is easier to digest than raw potato.
How does baking powder work?
Baking powder is added to cake mixes to help the cake rise during cooking. It contains sodium hydrogencarbonate. When this is heated, it breaks down and releases carbon dioxide.
Equation for the breakdown of sodium hydrogencarbonate
sodium hydrogencarbonate → sodium carbonate + carbon dioxide + water
2NaHCO3 → Na2CO3+H2O+CO2
What are food additives?
Food additives are substances added to food to improve its properties. Many food additives are natural substances such as vinegar. This preserves pickles and other food, and it gives the food a pleasant flavour.
Antioxidant purpose + example
Stops food reaction with oxygen and going off e.g Vitamin C
Food colour purpose + example
Gives food an improved colour which makes it more attractive e.g caramel
Flavour enhancer purpose + example
Improves flavour e.g monosodium glutamate
Emulsifier purpose + example
Stops oil and water separating e.g egg yolk lecithin
4 types of food additives
How do emulsifier molecules work?
Emulsifier molecules have a water-loving part (the hydrophilic end) and an oil-loving part (the hydrophobic end).The hydrophobic end of an emulsi er molecule bonds with oil molecules. The hydrophilic end bonds to water molecules. This stops droplets of oil or water forming and joining together, so helping to keep the mixture from separating.
What are perfumes?
Substances with pleasant smells
Perfume properties + reasons
Evaporates easily - The perfume particles must reach the nose easily.
Non-toxic (not poisonous)- It must not poison the user or make them ill.
Does not react with water - It must not react with perspiration.
Does not irritate the skin- It could not be applied to the skin if it would cause harm.
Insoluble in water - It must not be washed off easily.
Where can perfumes be obtained from?
Perfumes can be obtained from natural sources. These are often plant materials such as fruits, flowers, or certain woods, for example sandalwood.
What is volatility?
Volatility is a measure of how easily a liquid evaporates. Very volatile liquids evaporate easily. Perfumes evaporate easily because the attractions between their molecules are very weak and easily overcome.
What are esters?
compounds with pleasant smells. They are used in perfumes. Esters are found naturally in fruit but they can be made in the laboratory, too.
How can esters be made in laboratories?
by reacting an alcohol with an organic acid such as methanoic acid or ethanoic acid.
Word equation for creating esters
alcohol + acid → ester + water
Word equation for ethyl ethanoate
ethanol + ethanoic acid → ethyl ethanoate + water
Solutions, solvents, and solutes
A solution is a mixture of a solvent and a solute.
The solvent is the liquid that does the dissolving, and the solute is the substance that becomes dissolved.
Whether or not a substance will dissolve in a particular solvent depends upon the relative strength of the attractions between..
• the particles of the substance and the solvent molecules
• the particles of the substance itself
• the solvent molecules.
Why does nail polish not dissolve in water?
The attractions between the particles in nail varnish and water molecules are weaker than the attractions between the particles in nail varnish. They are also weaker than the attractions between water molecules.
What is a pigment?
a coloured substance used in paints or dyes.
What are the main three ingredients of paint and what are their functions?
- the pigment - gives the paint its colour
- binding medium - sticks the paint to the surface being pained
- solvent - thins paint so spreads better
Emulsion paints - what and how?
Emulsion paints are water-based paints. Their ingredients are dissolved in water. As the water evaporates, the paint dries and the other ingredients join together to form a tough, coloured layer on the painted surface.
The pigment is dispersed in an oil which may be dissolved in a solvent. The solvent in oil paints is a hydrocarbon oil. This evaporates as the paint dries, but something else happens, too. Oxygen in the air oxidises the hydrocarbon molecules. Eventually they join together to form a very tough layer on the painted surface.
What is a colloid?
a type of mixture in which one substance is spread or dispersed evenly in another substance. Colloids are different from solutions because none of the substances is dissolved.
Why do the components of a colloid not settle or separate out?
This is because the particles are dispersed throughout the mixture and are too small to settle.
What are thermochromic pigments?
sensitive to temperature. They change colour when they are heated up or cooled down. Some liquid crystals are thermochromic. Other thermochromic pigments are heat-sensitive dyes. They are usually colourless at one temperature and become coloured as the temperature is changed