|Chemistry C1 Flashcards
|Atoms are really tiny and have a nucleus which is positively charged, and electrons which are negatively charged. The electrons move around in layers known as shells. Atoms can form bonds to make molecules or compounds. It is the electrons which are involved in making bonds. Sometimes an atom loses an electron loses an electron making it charged positively and if it gains an electron it's overall charge is negative. Charged atoms are known as ions, if a positive ion meets a negative ion they will bond and form an ionic compound. The other main type of bond is called a covalent bond - atoms in a covalent bond share electrons.
|Additives are added to fod to make it ast longer and improve their colour and flavour. Antioxidants help to preserve food and emulsifiers help oil and water to blend together in foods like ice cream and salad cream
|Emulsifiers help oil and water to mix. Mixing water and oil makes an emulsion. Emulsions are made up of droplets of one liquid suspended in another liquid. Oil and water naturally want to separate into wo layers with oil floating on top of water. Emulsifiers are molecules which contain a hydrophilic head (hates oil) and hydrophobic tail (hates water). The hydrophilic head binds with the water molecules and the hydrophobic tail binds with the oil molecules. Oil droplets do not join together.
|Some foods are cooked so they have a better taste and texture or are cooked so they are easier to digest. Food can also be cooked so all the microbes that cause diseases are killed or because some foods are poisoness when raw and must be cooked so they are edible. Cooking foods produces new substances meaning there is a chemical change has happened. Eggs and meat are good sources of proteins. Protein molecules change shape when you heat them because the energy from cooking breaks some of the chemical bonds in the protein. This gives it an ediable texture and is known as denaturing. Potatoes are plants and each one has a rigid cell wall made from cellulose and humans cannot digest cellulose so the cook the potato. This ruptures the cell walls and make starch grains inside the cell swell and spread out which makes the potato softer so it's easier to digest.
|2NaHCO3 -> Na2CO3+CO2+H2O Baking powder when heated undergoes thermal decomposition. THERMAL DECOMPOSITION is when a substance breaks down into simpler substances when heated. Many of these reactions are helped along by a catalyst. Baking powder is used in cakes and the carbon dioxide is what makes the cakes rise. Carbon dioxide can be detected using limewater. It will turn cloudy when it's bubbled through if carbon dioxide is there.
|Perfumes can be natural and artificial. They are made up of esters. Acid + Alcohol -> Ester + Water A perfume needs to 1. EVAPORATE easily so that the particles can reach your nose. 2. NON-TOXIC so it doesn't poison you 3. NOT REACT WITH WATER so it doesn't react with sweat 4. NOT IRRITATE SKIN so you don't burn your skin. 5. INSOLUBLE IN WATER so it doesn't wash off easily. 6. BE VOLATILE particles in perfumes have weak forces of attractions between them so it's easy for the particles to escape and evaporate. Perfumes and cosmetics have to be tested thoroughly to make sure they're safe to use. Some people disagree that they should be tested on animals.
|Solids & Liquids
|In a SOLID there are strong forces of attraction between particles which holds them in a fixed position. Solids have a definite shape and volume. A solid's particles vibrate about their positions and the hotter it becomes the more they vibrate and move which causes them to expand when hot. A LIQUID has some force of attraction between their particles, they're free to move past each other but tend to stick together. Liquids don't keep a definite shape and will flow to fill a container. The particles are constantly moving with random motion. The hotter the liquid gets, the faster they move. This causes liquids to expand slightly when heated. GASES have no force of attraction between the particles, they're free to move and travel in straight line and only interact when they collide. Gases don't have a definite shape or volume and will always fill a container. The hotter it gets, the faster they move and gases either expand when heated or their pressure increases.
|When a liquid is heated, the heat energy goes into the particles allowing them to move faster, but some particles move faster than others. Fast-moving particles at the surface will overcome the forces of attraction from other particles and escape. This is evaporation. Volatility is how easily a liquid evaporates.
|Solvents & Solutes
|Solution - a mixture of a solute and solvent that doesn't separate out. Solvent - a liquid it's dissolving into. Solute - the substance being dissolved. Soluble - it can dissolve. Insoluble - it cannot dissolve. Solubility - a measure of how much it will dissolve. Nail Varnish doesn't dissolve in watee because the two substances are attracted to attracted to themselves more than each other so they don't form a solution. The nail varnish molecules are strongly attracted to each other, this attraction is stronger than the attraction between water molecules and nail varnish molecules. However, nail varnish dissolves in acetone because the attraction between the acetone molecules and nail varnish molecules is stronger than the attractions holding each substance together.
|Pigments & Colloids
|Pigments give paint their colour. Paints usually contain a pigment, binding medium and a solvent. The binding medium is a liquid that contains the pigments and holds them together. When the binding medium goes solid it sticks the pigments to the durface painted. The solvents thins the paint which makes it easier to spread. Paint is a colloid (particles of one substance are dispersed with particles of another substance - but they are not dissolved). These particles can be bits of solids, droplets of liquids or bubbles of gas. Colloids do not separate out because the particles are so small that they don't settle out at the bottom. Paint is a colloid because particles of a pigment (usually a solid) are dispersed through a liquid.
|Emulsion paints a water based, the water is the solvent and the binding medium is a acrylic or vinyl acetate polymer. The paint dries when the solvent evaporates which leaves behind the binder and pigment as a thin solid film. This paint is fast-drying and doesn't produce harmful fumes so are ideal for painting inside walls.
|Gloss paints are oil based paints, this oil is the binding medium and the solvent is an organic compound that'll dissolve oil. To dry, the solvent firstly evaporates and then the oil is oxidised before it turns into a solid. This paint is glossy, waterproof and hard wearing but the solvents used produce harmful fumes and take longer t dry. This is best outside walls and metal work.
|Thermochromic & Phosphorescent Pigments
|THERMOCHROMIC pigments change colour when there is a change in temperature. Different pigments change colour at different temperatures, so a range of these pigments can be used to make a colour-coded temperature scale. These are used in baby spoons, kettles and mugs. These pigments can be mixed with acrylic paints to give a wide range of colour changes. PHOSPHORESCENT pigments absorb light and store this light energy in their molecules and it is released as light. It is used in watches, traffic signs and novelty decorations. Radioactive paints could be used to make things glow for years, however this gave off atomic radiation and wasn't very safe.
|Plastic are long-chained molecules called polymers. Polymers are formed when small molecules (monomers) join together. Addition polymers are made from unsaturated monomers molecules (alkenes). Addition polymers are made up of monomers with a double covalent bond (unsaturated). These alkenes can open up their double bonds and join together to make a polymer chain.
|Properties of Polymers
|Strong covalent bonds hold the atoms inside a polymer chain together. But the forces between the chains determine the properties of the plastic. If the plastic is made up long chain which have weak intermolecular forces, the chains will be free to slide over each other. This plastic will have a low melting point and will be stretched easily. Some plastics have stronger bonds between he polymer chains - this can be due to stronger covalent bonds between the chain or cross linking bridges. These plastics have higher melting points, are rigid and can't be stretched because the cross linking bridges hold the chains together firmly.
|Polymer Properties & Examples
|Strong, rigid polymers are used for plastic milk bottles. Light, stretchable polymers are use for plastic bags and squeezy bottles, (this has a low melting point and cannot be used on hot things). PVC is strong and durable and it can be made rigid (window frames and piping) or stretchy (synthetic leather). Polystyrene foam is used in packaging to protect breakable things also the trapped air inside the foam makes it a good insulator which makes it good for coffee cups.
|Nylon and GORE-TEX
|Polymers are often use to make clothes. NYLON is a synthetic polymer which is not waterproof on it's own but is when coated with polyurethane to make it waterproof as well as tough, hard-wearing and keep UV light. Polyurethane doesn't let water vapour pass through though so sweat condenses and makes skin wet and uncomfortable - Nylon is not breathable. GORE-TEX is made by laminating a thin film of plastic called expanded PTFE onto a layer of another fabric such as Nylon, this makes the PTFE sturdier. PTFE has tiny holes which let water vapour through - so it's breathable. But it's also waterproof so the holes are not big enough to le water droplets through also, the PTFE repels liquid water.
|Most polymers aren't broken down by micro-organisms which means they do not rot. It's difficult to get rid of plastics in landfill sites because most aren't biodegradable. When plastics are burnt they release gases such as (acidic sulfur dioxide and poisonous hydrogen chloride and hydrogen cyanide). Sorting out lots of different plastics is expensive and difficult even though this is the best way to reuse plastics.
|CnH2n+2 Alkanes are saturated compounds which means they are singled bonded. An alkane will not decolourise in bromine water. Alkanes will not form polymers. The first four are methane (CH4), Ethane (C2H6), Propane (C3H8) and Butane (C4H10).
|CnH2n Alkenes are unsaturated compounds meaning that they contain at least one double covalent bond. An alkene will decolourise in bromine water. The bromine water will make the alkene a colourless dibromo compound. Their double bonds between the carbon atoms can break and make new bonds meaning it is much more reactive than alkanes and can form polymers. The first three compunds are Ethene (C2H4), Propene (C3H6) and Butene (C4H8).
|Crude oil is a fossil fuel formed from the dead remains of plants and animals. Over millions of years, with high temperature and pressure, the remains get turned into crude oil which can be drilled up. The different compounds in crude oil can be separated by fractional distiliation. The oil is heated until most of it has been turned into gas, the gases enter the fractioning column. Long hydrocarbons have high boiling points , they turn back into liquids and drain out of the column early on when they're near the bottom. The shorter hydrocarbons have lower boiling points and turn back into liquid and drain out much later on, near the top of the column. You end up with the crude oil mixture separated out into different sections.