Chemistry Topic 4 - Chemical Changes

State whether the following pH values are acidic, alkaline or neutral. a) 9, b) 2, c) 7, d) 6
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State whether the following pH values are acidic, alkaline or neutral. a) 9, b) 2, c) 7, d) 6
a) alkaline, b) acid, c) neutral, d) acid
Give the general word equation for the reaction between an acid and a base
acid + base -> salt + water
What type of reagent could be used to show that an acid or base has been completely neutralised?
Metal carbonates
Why should you first carry out a rough titration when carrying out a titration experiment?
To get an approximate idea of where the solution changes colour
Why shouldn't you use Universal indicator as an indicator in a titration?
Universal indicator is used to estimate the pH of a solution because it can turn a variety of colours, each indicating a narrow range of pH values. In a titration, you're looking for a sudden colour change at the end-point.
Name two suitable indicators for a titration between an acid and an alkali, and state their colours when in acidic and alkaline solutions.
Litmus - blue in alkalis, red in acids
Phenolphthalein - pink in alkalis, colourless in acids
Methyl orange - yellow in alkalis, red in acids
What is a strong acid?
An acid which completely splits up into its ions in water. E.g. when HCl is in water all the HCl molecules split up into H⁺ and Cl⁻
By what factor does the H+ concentration increase for a decrease of 1 on the pH scale?
10
Explain the difference between a strong acid and a concentrated one.
Acid strength = what proportion of the acid molecules ionise in water. Concentration = how much acid there is in a certain volume of water.
Is zinc more or less reactive than iron?
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What is the general word equation for the reaction of a metal with an acid?acid + metal -> salt + hydrogenGive the balanced equation for the reaction of calcium with water.Ca + 2h20 -> Ca(OH)2 + H2Will copper react with water?NoWhat product forms in the oxidation of magnesium by oxygen?Magnesium oxideExplain how you decide whether a metal can be extracted from its oxide by reduction with carbon.If a metal is less reactive than carbon, it can be extracted from its oxide by heating with carbon.Why is gold found as itself in the earth?Gold is highly unreactiveIn terms of electrons, give the definition of oxidation.Loss. (OIL RIG - Oxidation Is Loss, Reduction Is Gain)In a displacement reaction, does the metal atom get reduced or oxidised?In displacement reactions, it's always the metal ion that gains electrons and is reduced. The metal atom always loses electrons and is oxidised.During electrolysis, which electrode are the positive ions attracted to?Negative electrodeWhy can ionic solids not undergo electrolysis?Ionic compounds in the solid state cannot conduct electricity since they have no free ions that can move and carry the charge. The ions must be able to move and can only do so in the molten state or when dissolved in a solution, usually aqueous.Do ions get reduced or oxidised at the anode?oxidisedDuring the manufacture of aluminium from bauxite, which electrode is aluminium formed at?The pure aluminum is attracted to the cathode, which is a lining of graphite.In what situation will hydrogen gas be given out during the electrolysis of an aqueous solution of an ionic solid?Hydrogen will be produced if the metal is more reactive than hydrogen.If halide ions are present in an aqueous solution of an ionic solid will oxygen gas be released?Oxygen is produced (from hydroxide ions), unless halide ions (chloride, bromide or iodide ions) are present. In that case, the negatively charged halide ions lose electrons and form the corresponding halogen (chlorine, bromine or iodine).What test could you use to determine if hydrogen gas has been produced in an electrolysis reaction?Squeaky pop - lighted splint goes out with a squeaky pop noise