Halogen displacement reactions
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What can a more reactive halogen do to a less reactive halogen?
displace it from its compounds
investigating displacement practical
• adding a halogen solution to a metal halide solution • see if the mixture darkens, indicating a reaction -chlorine in ‘chlorine water’ displaces bromine from sodium bromide solution CL2 + 2NaBr -> 2NaCl + Br2 ionic equation (Na+ ions are spectator ions): Cl2(aq) + 2Br-(aq) -> 2Cl-(aq) + Br2(aq)
redox reaction
a reaction in which both oxidation and reduction happens
define oxidation and reduction
Oxidation Is Loss of electrons Reduction Is Gain of electrons (OIL RIG)
What type of reaction are halogen displacements
redox reactions e.g.: chlorine displaces bromine from bromide ions in solution 1) chlorine atoms gain electrons and are reduced to chloride ions 2) bromide ions lose electrons and are oxidised to bromine
Explain a redox reaction using chlorine and sodium bromide as an example
-chlorine is added to sodium bromide (Cl2 + NaBr) -both substances have a neutral charge -chlorine displaces bromine to make sodium chloride (Cl2 + NaBr -> NaCl + Br2) -chlorine and bromine swap places balanced: Cl2 + 2NaBr -> 2NaCl + Br2 ionic equation: -as Na is removed from the equation, the other elements in the compound gain a charge -the charge is negative because group 7 elements form 1- ions Cl2 + 2Br- -> 2Cl- + Br2 (the charges are always shown in the upper right of the symbol)
How do you write half equations, using chlorine and sodium bromide as an example?
the loss or gain of electrons is always shown by + ne- the e- represents the charge of the lost/gained electrons the n is how many are gained or lost the electrons are never - from the equation in reduction the electrons are shown on the left side to indicate a gain of electrons: Cl2 + 2e- -> 2Cl- in oxidation the electrons are shown on the right to indicate a loss of electrons/the electrons separating from the substance: 2Br- -> Br2 + 2e- (the substances are balanced as the uncharged atoms exist in pairs)
A student adds a few drops of halogen solutions to small volumes of potassium halide solutions on a potting tile. The three halides and halogens used are chlorine, bromine and iodine State which potassium halides are displaced by: a) chlorine b) bromide c) iodide
a) bromide and iodide b) iodide c) none of them
Aqueous bromine solution reacts with aqueous potassium iodide solution a) write the balanced equation and the ionic equation b) explain, with the help of half equations, why this reaction is a redox reaction
a) Br2(aq) + 2KI(aq) -> 2KBr(aq) + I2(g) Br2 + 2I -> 2Br + I2 b) bromide atoms (in Br2) gain electrons and are reduced to bromide ions Br2 + 2e- -> 2Br- Iodide ions lose electrons and are oxidised to iodine 2I- -> I2 + 2e-
State and explain whether astatine will react with potassium iodide solution
astatine will not react with potassium iodide solution because • reactivity decreases down group 7 • astatine is less reactive than iodine
ionic equation
an equation that includes the charges of the ions spectator ions can be left out
spectator ions
ions that are unchanged (in charge) during a reaction e.g. Na in the reaction of chlorine with sodium bromide
In a redox reaction, what happens to: a) atoms that gain electrons b) ions that lose electrons
a) they are reduced to chloride ions (‘reduced’ because reduction is gain of electrons) b) they are oxidised to atoms
Why are atoms that gain electrons described as ‘reduced’ to ions?
reduction is the gain of electrons