The Purpose of Titration of a Weak Acid
When scientists change an acid solution by adding a base solution to it, this is known as titration. Through controlled titration, scientists can learn the exact concentration of an acidic solution. This process can also be performed to neutralize the acidic solution. Titrating weak acids with strong bases creates a neutral or basic solution.
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What Is an Acid?
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Acids are sour-tasting solvents that produce positive hydrogen ions when mixed into water or other aqueous solutions. Mixing an acid with a base causes a chemical reaction resulting in the production of water and some type of salt. Acids release hydrogen gas when they touch metal.
Acids can be said to be strong or weak. A strong acid, in chemical terms, is an acid that contains a high percentage of hydrogen ions. A weak acid contains a low percentage of hydrogen ions. The weaker the acid, the more similar it is to pH-neutral water.
Common acids include citric acid, found in oranges and other citrus fruits; acetic acid, found in vinegar; and carbonic acid, found in soft drinks.
What Is a Base?
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Base solutions are the opposite of acid solutions. These solutions have a bitter taste and a slippery feel. They are found in common household products such as soap and laundry detergent.
A strong base has a high concentration of hydroxide ions, while a weak base has a low concentration of hydroxide ions. When combined with acids, bases generate water and salts.
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What Is Titration?
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Titration refers to the process of combining acids with bases. Scientists often perform this process to determine the level of hydrogen ion concentration in an acid or to neutralize the acid. A strong acid may be titrated with a strong or weak base, and a weak acid may be titrated with a strong base. It is unusual to titrate a weak acid with a weak base because the change in the solution would be insignificant and difficult to detect.
Method
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To titrate a weak acid with a strong base, scientists use a solution known as a standard solution in addition to the titrant solution. The standard solution is a solution of a known concentration, such as sodium carbonate. The titrant solution is a solution of unknown acidity.
The scientist first rinses a burette with the standard solution and a pipette with the titrant solution. She then fills a conical flask with distilled water and fills the burette to the top with the standard solution.
With the pipette, the scientist introduces a pre-determined amount of the titrant solution into the water, along with a small amount of an indicator substance. The indicator substance will change color when the acid and base react to each other.
The scientist slowly lets the standard solution out of the burette and into the flask. When the solution in the flask turns pink, the acid and base have neutralized each other. The scientist reads the burette to determine how much of the standard solution was used.
The experiment is repeated three more times. The first result is usually considered a rough estimate and is not used.
Determining pH
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After completing the titration, scientists can estimate how acidic the original solution was by examining the color of the indicator and averaging how much standard solution it took to neutralize the solution. They can also perform a mathematical calculation to determine the pH level of the original solution. A pH level less than 7 indicates a basic solution, while a pH level greater than 7 indicates an acidic solution. A weak acid will have a pH level closer to 7 than a strong acid.
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References
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