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pH indicators by Mind Map: pH indicators
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pH indicators

pH scale

has a set of numbers 1-14

used to indicate whether solution is acidic, alkaline or neutral

acids have pH values less than 7

eg, HCl pH 1, Sulfuric Acid pH 1

acids with smaller pH values have higher concentration of Hydrogen ions

alkalis have pH values more than 7

eg, NaOH pH 13

alkaline solns with larger pH value have higher concentration of hydroxide ions

a neutral soln (eg a salt soln or water) has a pH value of 7

has equal number if hydrogen and hydroxide ions

pH is used to compare strength of acid and alkali

indicators

are substances that change colour when acidic or alkaline soln added to them

Universal indicator

Very acidic-red

acidic-orange,yellow

neutral-green

basic/base/alkali-blue

very basic/base/alkali -purple

Methyl Orange

Turns red in acidic soln

Turns Yellow in alkaline soln

Changes colour at pH 3 - 5 range

Litmus paper

Blue litmus turns red when in acidic soln

red litmus turns ble when in alkaline soln

phenolphthalein

colourless in acidic soln

yellow in alkaline soln

changes colour at pH 8 - 10 range