topic 3: chemical changes

Question 1

acid

Answer 1

produces hydrogen ions (H+) in aqueous solutions with a pH range between 0 and 7

Question 2

alkali

Answer 2

produces hydroxide ions (OH-) in aqueous solutions with a pH range betrween 7 and 14

Question 3

anode

Answer 3

the positive electrode. it is where negatively charged ions lose electrons in oxidation reactions. it is the electrode where oxygen is produced unless the solution contains halide ions - then the halogen is produced

Question 4

base

Answer 4

a substance which reacts with an acid in a neutralisation reaction to form salt and water only

Question 5

cathode

Answer 5

the negative electrode. it is where positively charged ions gain electrons in reduction reactions. is the electrode where hydrogen is produced if the metal in the electrolyte is mrore reactive than hydrogen.

Question 6

electrode

Answer 6

a solid conductive material through whihc electricity can flow. they are used in electrolysis to conduct electricity

Question 7

electrolysis

Answer 7

the splitting up of an ionic compound using electricity. the electric current is passed through a substance causing chemical reactions at the electrodes which lead to the decomposition of the materials

Question 8

electrolyte

Answer 8

a solution containing free ions from the molten or aqueous ionic substance. the ions are free to move to carry charge

Question 9

indicators

Answer 9

a chemical used in a titration reaction to identify the end point of the reaction by a clear colour change

Question 10

neutralisation

Answer 10

the reaction in which an acid and a base react to form a salt and water

Question 11

oxidation

Answer 11

a reaction involving the gain of oxygen. oxygen is the loss of electrons

Question 12

pH scale

Answer 12

a measure of the acidity or alkalinity of a solution. the scale ranges from 0-14 and can be measured using universal indicator or a pH probe

Question 13

reduction

Answer 13

a reaction involving the loss of oxygen. reduction is the gain of electrons.

Question 14

strong acid

Answer 14

an acid which is completely ionised in an aqueous solution so that nearly all the H+ ions are released. examples of strong acids include hydrochloric, nitric and sulphuric acids.

Question 15

titration

Answer 15

a technique used where a solution of known concentration is used to determine the concentration of an unknown solution

Question 16

universal indicator

Answer 16

a mixture of dyes that change colour gradually over a range of pH and is used in testing acids and alkalis

Question 17

weak acid

Answer 17

an acid which is only partially ionised in an aqueous solution. this means only a small number of the H+ ions are released. examples of weak acids include ethanoic, citric and carbonic acids