indicators in chemistry and everyday life. indicators summary introduction definition of ph acids...

INDICATORSin chemistry and everyday life

INDICATORS

SUMMARY

Introduction

Definition of pH

Acids and bases

Bromothymol blue

Natural indicators

pH paper

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2.

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A pH indicator is a halochromic chemical

compound that is added in small amounts to a solution

in order to determinate easily the pH (acidity or

alkalinity) of the solution.

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pH is a mathematic tool used in chemistry to measure acidity of a solution

mathematic definition for diluted solutions :

usual pH range : 0-14

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pH indicators exist under severals forms of acide-base couples :

InH in acidic solutions (1st colour)In- in basic solutions (2nd colour)

-> So, the colour of the solution can give us informations about acidity of the solution

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Bromothymol blue is the most famous coloured indicator

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C : pH in transition range of BBT

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A : acid form of BBT

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

350

370

390

410

430

450

470

490

510

530

550

570

590

610

630

650

Wavelenght (nm)

Ab

sorb

ance A

B

C

B : basic form of BBT

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We can find a lot of natural indicators in the nature :

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- Red cabbage (red–pink–violet–blue–green–yellow)- Turmeric / Curry (yellow-orange-brown)- Tea (yellow-brown)- Rose petals (blue-pink)- Artichoke (colorless-yellow)- …

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pH paper (Hydrion Paper) is a paper which contains a Universal Indicator

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"Universal Indicator" means severals indicators mixed in order to emit a different color for each pH value

pH paper is red in acid solutions and purple in basic solutions

acidic basic

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