What Is Titratable Acidity?
An acid is a material that can release a hydrogen ion. A hydrogen ion has a positive charge and is made out of a single subatomic particle called a proton. Many different chemicals are acids. Hydrogen chloride, for instance, is a molecule made out of chlorine and hydrogen. It is considered an acid because, when mixed with water, it dissolves into chlorine ions and hydrogen ions. Many other substances exhibit this ability. To measure the acidity of a substance, you can measure it with a chemical reaction process called “titration.”
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Bases: The Key To Determining Titration Acidity
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The key to understanding titration acidity measurements is understanding bases. A base is in many ways the opposite of an acid. A base (also called an alkali) is a material that can release a hydroxide ion. A hydroxide ion is an oxygen ion bonded with a hydrogen ion. It has a negative charge. Many different substances, such as sodium hydroxide, are bases.
pH
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Acids and bases are measured on the pH scale. The pH scale is a series of numbers ranging from one to fourteen. Every substance has a number describing how much acid or base it is. Seven is a neutral number, and indicates the substance has no acidity or alkalinity. Any number above seven indicates a base, with larger numbers indicating greater alkalinity. Any number below seven indicates an acid, with smaller numbers indicating greater acidity.
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Acid/Base Reactions
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When an acid is mixed with a base, they react. The positive charge of the hydrogen ions and the negative charge of the hydroxide ions are attracted to each other, because opposite electrical charges attract. When they meet, they bond. The oxygen and hydrogen of the base combine with the hydrogen of the acid, and the resulting molecule is a single oxygen bonded with two hydrogens. This is H2O, or water.
The Principle
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Acids and bases neutralize each other by forming water. Because of this, the acidity of a substance of unknown acidity can be determined by mixing it with a base of known alkalinity. By carefully measuring exactly how much base it took to neutralize the acidity of the substance being examined, the acidity of that substance can be calculated. This process is called titration.
Equipment
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There are only three items needed to measure titration acidity. One is some kind of container like a flask to hold the substance you are testing. The second is a special kind of container called a buret. This is a long glass tube with a spout at the bottom that can be turned on and off. If a buret is impossible to find, then an eyedropper can be used to transfer the base from one container to the other. The third thing needed for titration is some way of measuring the pH level of the unknown solution, such as a pH meter or litmus paper.
The Procedure
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The procedure, as described by Dartmouth College's Chem Lab, is fairly straightforward. The buret should have volume markings all along its length. To titrate the acid, you first record the volume of the base in the buret. Then you open the spout on the buret and let a very small amount of base out into the acidic solution. After this, read the pH of the solution. Repeat these steps as necessary. When it reaches seven, then all of the acid has been neutralized by the base you have mixed with it. Read the final volume of base in the buret and figure out how much base was used. This figure can be put into a formula and used to determine the titratable acidity of the original solution.
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