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6.1 |
The Role of Water in Showing Acidic and Aklaine Properties |
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Acid |
- Acid is a chemical compound that produces hydrogen ions, \(H^+\) or hydroxonium ions, \(H_3O^+\) when dissolved in water.
- The dissociation of acid in water produces hydrogen ions and an anion.
- An example of dissociation of hydrochloric acid in water is as follows;;
- \(HCl(aq) \xrightarrow[]{H_2O} H^+ (aq) + Cl^- (aq)\)
- Without the presence of hydrogen ions, that means there are no acidic properties on the chemicals.
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Basicity of Acid |
Definition of Basicity of Acids |
- Refers to the number of hydrogen ions, đ»+ that can be produced by an acid molecule that ionises in water.
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Classification of Acid based on Acidity |
Monoprotic Acid |
Diprotic Acid |
Tripotic Acid |
One \(H^+\) per acid molecule |
Two \(H^+\) per acid molecule |
Three \(H^+\) per acid molecule |
Hydrochloric acid, \(HCl\) |
Sulphuric acid, \(H_2SO_4\) |
Phosphoric acid, \(H_3PO_4\) |
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Alkali |
- The base is a chemical compound that can neutralise an acid to produce salt and water.
- Example of formation of salt and water is:
- \(HCl (aq) + NaOH(aq) \rightarrow NaCl (aq)+ H_2O(l)\)
- Most bases are not soluble in water.
- Bases that are soluble in water are known as alkalis.
- Bases that insoluble in water are zinc oxide, zinc hydroxide, copper(II) oxide and copper(II) hydroxide.
- An alkali is a chemical compound that dissolves in water and produces freely moving hydroxide ions, \(OH^-\).
- Without the presence of hydroxide ions, the chemical substances do not show alkaline or basic properties.
- Example of alkali is potassium hydroxide:
- \(KOH(aq) \xrightarrow[] {H_2O}K^+(aq) + OH^-(aq)\)
- Example of alkali;
- Sodium hydroxide, \(NaOH\)
- Potassium hydroxide, \(KOH\)
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Definition of Alkali |
Chemical compound that dissolves in water and produces freely moving hydroxide ions, \(OH^-\). |
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Uses of Acids, Bases and Akalis in Our Daily Life |
Acid |
Uses |
Sulphuric acid |
Make paints, polymer, fertilisers and detergent |
Hydrochloric acid |
To clean metal before electroplating |
Benzoic acid |
To preserve food |
Bases |
Uses |
Ammonia |
Make fertilisers, nitric acid, and to maintain latex in liquid form |
Magnesium hydroxide |
To make toothpaste, gastric medicine |
Calcium hydroxide |
To make cement, limewater and to neutralise acidic soil |
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The Role of Water to Show Acidity and Alkalinity |
- Acids only show acidic properties in the presence of water.
- When an acid is dissolved in water, acid molecules will ionise to produce hydrogen ions, \(H^+\).
- The presence of hydrogen ions \(H^+\) allows the acid to show its acidic properties.
- Therefore, blue litmus paper changes to red.
- Without water, solid oxalic acid, C2 H2 O4 only exist as molecules.
- Hydrogen ions, \(H^+\) are not present.
- Thus, the colour of blue litmus paper remains unchanged.
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![The image is a diagram showing different types of indicators. At the center, there is a blue circle labeled âIndicator.â Four arrows point to this central circle from four surrounding circles. The surrounding circles are labeled as follows: âMethyl orangeâ (top left), âUniversal indicatorâ (top right), âBlue litmus paperâ (bottom left), and âRed litmus paperâ (bottom right). The background is white, and the text is in blue. The Pandai logo is at the bottom center of the image.](https://app.pandai.org/uploads/image/134073/Indicator.jpg) |
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Indicators and their Colours in Acid and Alkaline Solution |
Indicator |
Colour of Indicator in Acidic Solution |
Colour of Indicator in Alkaline Solution |
Methyl orange |
Red |
Yellow |
Universal indicator |
Red for strong acid and yellow for weak acid |
Purple for strong alkali and blue for weak alkali |
Blue litmus paper |
Red |
Blue |
Red litmus paper |
Red |
Blue |
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