How Could You Determine The Acidity of Household Items?
Acidity:
The level, or concentration of hydrogen ions found within a solution containing a dissolved acid.
Acidity could also refer to the strength of an acid, its ability or tendency to dissociate and release these positive hydrogen ions.
Household Items Containing Acids:
Vinegar (Acetic Acid)
Lemon Juice (Citric Acid)
Yoghurt (Lactic Acids)
Batteries (Hydrochloric Acid)
Vitamin C (Ascorbic Acid)
Tartaric Acid (used in baking)
Aspirin and some other forms of medication (Salicylic Acid)
Sprite - Citric Acid, Phosphoric Acid
Factors That Affect The Acidity of A Substance
Acids:
In chemistry, acids are a particular class of hydrogen-containing substances which can be found in molecular or ionic form. They are usually identified by their ability and tendency to donate protons. However, acids can be differentiated and further broken down into separate groups
Organic Acids:
Are organic compounds with acidic properties. As opposed to Inorganic acids, these are generally weaker, are poorly soluble in water, and less reactive. Examples include: Citric and Acetic acid.
Inorganic Acids:
Also known as mineral acids; they are acidic compounds derived from inorganic substances. These are highly soluble in water and are generally considered to be strong. Examples include sulfuric and hydrochloric acid.
The Arrhenius Definition:
Acids are substances that produce H+ ions when placed in an aqueous solution. Whereas its counterpart bases, produce OH- .
Lewis Acids
A species able to accept electron pairs to form covalent bonds.
Brønsted-Lowry Acids:
Cateogrised as a general group of acids that can donate protons in chemical reactions between chemical species
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.
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
Methods of Measuring and Determining
the Acidity of Substances:
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
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.
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
Concentration: The higher the concentration of the acid, would directly increase the amount of dissociation occurring and the presence of hydrogen ions found in a solution. In order to conduct a fair test comparing acids, the concentration should be kept the same.
Conjugate Bases: The weaker the conjugate base, the stronger the acid it interacts with. Thus, any factor that stabilizes bases will increase the acidity of an acid.
Structure: Acidity can also be described as the strength of an acid, or its ability to dissociate. The acid-base strength of a molecule depends greatly on its structure. The weaker the bonds A–H or B–H+ bond, the more likely it is to dissociate to form an H+ ion.
The Resonance Effect: When the negative charges of an ion is shared between delocalised electrons. When electrostatic charges are spread-out and shared, they become more stabilised. Changes in the degree of resonance within bases can affect the tendency of its electrons to leave and form bonds with acidic protons. Thereby weakening the strength or tendency of an acid to dissociate.
Safety
Household items that are acidic are often diluted. Still, they can pose risks during everyday life or in lab experiments depending on concentration, volume, or area of contamination.
Safety Considerations During Experiments:
Be fully clothed and wear correct PPE Wear closed shoes and eye protection
- Handle with caution and care
- Use diluted versions of the acids
- Do not place the acid near electrical appliances or near edges
- Wear closed shoes
These household items contain acids at varying concentrations and with varying strength. If an experiment was designed including some of these acids, these two aspects should be taken into account in order to create a method that can be followed to obtain substantial and accurate results. Certain acids are found in low quantities such as citric, and some are much higher such as Salicylic Acid.
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
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
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.
These are the controlled variables that need to be kept constant in any type of investigation in order to produce valid results
In the case of acid-skin contact; immediately wash with lukewarm water
In the case of acid spillage, immediately clean with an absorbent pad/pillow to avoid further spread
To dispose of these acids, pour directly down a drain. Diluting it beforehand is also applicable but not always necessary as household items are not necessarily dangerous or corrosive