NSSCO Chemistry (6117) flashcards
NSSCO Chemistry (6117) · Build recall with a focused review session.
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- Diffusion
- Net movement of particles from a region of higher concentration to lower concentration, caused by random motion; it is faster at higher temperatures.
- Sublimation
- Change of state directly from solid to gas without passing through the liquid state; iodine and dry ice sublime under suitable conditions.
- Pure substance
- A substance with fixed composition and sharp melting and boiling points; it may be an element or a compound, not a mixture.
- Filtration
- Separation of an insoluble solid from a liquid by passing the mixture through filter paper; the solid remains as residue and the liquid is filtrate.
- Chromatography Rf value
- Ratio of the distance travelled by a spot to the distance travelled by the solvent front in paper or thin-layer chromatography; it helps identify a substance.
- Simple distillation
- Separation of a solvent from a solution by boiling the mixture and condensing the vapour; it can produce pure water from salt solution.
- Atomic number
- Number of protons in the nucleus of an atom; in a neutral atom it equals the number of electrons and determines the element's identity.
- Mass number
- Total number of protons and neutrons in the nucleus of an atom; neutrons equal mass number minus atomic number.
- Isotopes
- Atoms of the same element with the same number of protons but different numbers of neutrons; they have identical chemical properties but different masses.
- Ionic bond
- Strong electrostatic attraction between oppositely charged ions formed when a metal transfers electrons to a non-metal.
- Covalent bond
- A bond formed by the sharing of one or more pairs of electrons between atoms, usually between non-metal atoms.
- Metallic bond
- Attraction between a lattice of positive metal ions and a sea of delocalised electrons; it explains electrical conductivity and malleability.
- Mole
- The amount of substance containing 6.02 × 10^23 particles; one mole of any substance has a mass equal to its molar mass in grams.
- Molar mass
- Mass of one mole of a substance in grams per mole; it is numerically equal to the relative formula mass.
- Concentration
- Amount of solute in moles dissolved in one cubic decimetre of solution; calculated as moles divided by volume in dm3.
- Acid
- A proton donor; in water it releases hydrogen ions, H+, and has a pH below 7.
- Neutralisation
- Reaction between an acid and a base producing a salt and water; the ionic equation is H+ + OH- -> H2O.
- Alkali metals
- Group 1 elements, soft and reactive metals that form +1 ions and react with water to give hydrogen and an alkaline solution.
- Halogen displacement
- A more reactive halogen displaces a less reactive halogen from its salt solution; chlorine displaces bromide but iodine cannot displace chloride.
- Galvanising
- Coating iron or steel with zinc to prevent rusting; zinc is more reactive and corrodes in preference to iron.
- Alloy
- Mixture of a metal with other elements; alloy layers resist sliding, making the material harder than the pure metal.
- Haber process
- Industrial production of ammonia from nitrogen and hydrogen using an iron catalyst, high pressure and moderate temperature; ammonia is used for fertilisers.
- Greenhouse gas
- Gas such as carbon dioxide or methane that absorbs infrared radiation and warms the atmosphere; human activity increases their concentration.
- Catalyst
- Substance that increases reaction rate by lowering activation energy and providing an alternative pathway; it is not used up overall.
- Exothermic reaction
- A reaction that releases heat to the surroundings; the products have less enthalpy than the reactants and ΔH is negative.
- Le Chatelier principle
- If a change is made to a system at equilibrium, the equilibrium shifts in the direction that opposes the change; temperature, pressure and concentration can cause shifts.
- Alkene
- Hydrocarbon with one carbon-carbon double bond and general formula CnH2n; it rapidly decolourises bromine water at room temperature.
- Addition polymerisation
- Joining of many alkene monomers to form a polymer; the double bonds open and no other product is formed.
- Independent variable
- The variable that is deliberately changed in an investigation; the dependent variable is measured while control variables are kept constant.
- Accuracy
- How close a measured value is to the true value; it differs from precision, which describes how close repeated measurements are to each other.
- Carbon dioxide test
- Bubble the gas through limewater; carbon dioxide turns limewater milky or cloudy because insoluble calcium carbonate is formed.
- Flame test
- Heating a clean wire with a sample in a flame gives characteristic colours: lithium red, sodium yellow, potassium lilac, calcium orange-red and copper blue-green.