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3.1.1 Acids & Bases - Coggle Diagram
3.1.1 Acids & Bases
Defining Acids & Bases
When alkalis are added to water, they form negative hydroxide ions (OH–)
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The pH scale is a numerical scale which is used to show how acidic or alkaline a solution is, in other words it is a measure of the amount of the ions present in solution
When acids are added to water, they form positively charged hydrogen ions (H+)
The pH Scale
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All acids have pH values of below 7, all alkalis have pH values of above 7
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Indicators
Many plants contain substances that can act as indicators and the most common one is litmus which is extracted from lichens
Synthetic indicators are organic compounds that are sensitive to changes in acidity and appear different colours in acids and alkalis
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Phenolphthalein and methyl orange are synthetic indicators frequently used in acid-alkali titrations
Two Colour Indicators
Synthetic indicators are used to show the endpoint in titrations as they have a very sharp change of colour when an acid has been neutralised by an alkali and vice-versa
Litmus is not suitable for titrations as the colour change is not sharp and it goes through a purple transition colour in neutral solutions making it difficult to determine an endpoint
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Litmus is very useful as an an indicator paper and comes in red and blue versions, for dipping into solutions or testing gases