Methods of Measuring Acid Content and
Concentration:
pH Meter:
This device is able to measure the acidity or alkalinity of a given substance, whether found in the liquid, semi-solid or solid state, therefore applicable for many household items. The meter is able to measure the degree of acidity by measuring the relative amount of free hydrogen and hydroxyl ions released. Substances with more free hydrogen ions are acidic, whereas ones with more free hydroxyl ions are basic.
However, it should be mentioned that this scale is unable to measure or determine the concentration of a given acid within a substance , rather just how acidic the substance given is. Unified, absolute pH meters are extremely accurate and consistent with measurements.
Indicator Papers
This is an inexpensive method of determining the acidity of a substance through colour change, using organic dye, similar to a pH scale. Although easy to implement and use consistently, the results of indication papers are not considered to be greatly accurate and other techniques should be favoured instead, especially considering the fact that many household items that are acidic, can contain components that will give conflicting results.
Indicator papers can be used as a method of measuring the acidity between largely different acids. It would not be found useful for example in an experiment comparing the acidity and concentration of ethanoic acid between different types of vinegar
Possible Investigation With Household Items:
Using the speed, accuracy and efficiency of pH scales, an experiment could be devised measuring and comparing the degree of acidity between organic and inorganic acids. This would be the independent variable.
Important controlled variables to ensure valid results include:
- the same volume and concentration of each acid is used and tested
- Same usage of the calibrated pH meters
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Titration:
A very effective and accurate, but difficult and somewhat lengthy process of determining the concentration of an acid with quantitative analysis. This is done through repeated trials of neutralising the acid of interest with a standard, basic solution and finding the volume. This technique is only applicable for household items in liquid state and with using a known volume. A pH-sensitive indicator dye, usually phenolphthalein, is used to show the endpoint of the experiment
Possible Investigation With Household Item:Titration can be used to find the acidity content in household drinks that are colourless such as Sprite. Sprite can contain many acids such as citric acid. Since there are many acids found within it, it will not be possible to find the concentration of each specific acid unless they are separated beforehand. The results of titration can find the degree of acidity within sodas such as sprite and be used to explain their effect on on teeth enamel erosion Important controlled variables to ensure valid results include:
- the same volume and concentration of each acid is used and tested
- Temperature is controlled at each trial
- The same amount of titrant is used in all trials
Titration is by far the most accurate and reliable method of measuring and determining the acid concentration of an analyte solution. It should be used to determine and differentiate levels of acidity between many common household items. An interesting experiment could be which type of vinegar contains the most amount of ethanoic acid? Thereby determining the most flavourful and useful vinegar.
The Acid Dissociation Constant
The Acid Dissociation Constant (Ka) is used to determine and differentiate between strong and weak acids. The stronger an acid is, the more it dissociates, represented by a higher (Ka) value. A weak acid is less likely to ionise and release a hydrogen ion, leading to a less acidic solution.
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Possible Investigation With Household Item:
The AD Constant can be used as a measuring tool to find the the extent to which an acid dissociates in solution and therefore its strength; which is would be the dependent variable. constant (Ka) is calculated using the equation Ka = [H+][A-]/[HA], where [H+] is the concentration of hydrogen ions, [A-] is the concentration of the base, and [HA] is the concentration of the acid.This method can be used to measure the strength of vinegar or lemon juice through their dissolution in water.Important controlled variables to ensure valid results include:
- the same volume and concentration of each acid is used and tested
- Temperature is controlled at each trial
The acid dissociation constant is more often implemented as a device to measure the dependent variable; the acidity of the acid in question. In order to reach this step, other techniques that can determine the amount of hydrogen ions released such as through logarithmic calculations
