How could you determine the acidity of household items?
What is acidity?
Acidity is the representation of the concentration of hydrogen ions (H+) in substances and its ability to donate protons (hydrogen ion).
What are acids?
An acid is a substance characterised by properties such as; sour in taste, it changes blue litmus paper to red, reacts with bases to form salts.
(Acid | Definition, Examples, Types, Uses, & Facts | Britannica 2023)
What are bases?
Bases are chemical compounds or solutions that can accept protons (H+ ions) from acids.
Bases are have the ability to neutralize acids which results in the formation of water and salt compound. Bases turn red Litmus paper to blue. Bases are also usually slippery to touch.
(Admin 2019)
Types of acids
Organic acids:
An organic acid contains carbon in its molecular structure and are commonly found in various natural sources such as fruits (Citric Acid from citrus fruits) or during fermentation processes (Lactic Acid in yohgurt). They are weak acids and partially disassociate in water, often having a lower acidity level in comparison to inorganic acids.(Panda et al. 2016)
Inorganic acids:
Inorganic acids are acids that do not contain carbon in their molecular structure. They can be found in sources such as minerals or synthesized in laboratories as well as found naturally in the environment in low concentrations. They are strong acids and are highly corrosive and completely dissasociate in water. having a higher acidity (eg. Sulfuric Acid and Nitric Acid) (Inorganic Acids | Thermo Fisher Scientific 2023)
Weak acids:
Weak acids only partially dissociate in water which results in a lower concentration of hydrogen ions (H+)
Strong acids:
Strong acids completely dissociate in water which means that they release a high concentration of hydrogen ions (H+)
What is acidity a measure of?
Acidity is the measure of the concentration of hydrogen ions present in a solution.
(BYJU'S 2022)
Where can acids be found?
Household products: Toilet cleaner (Commonly Citric Acid C₆H₈O₇, Hydrochloric acid HCL, Ammonia NH3), Stain removing products (Commonly Acetic Acid CH₃COOH, Acetone C3H6O),
Bodily fluids: Hydrochloric Acid HCl (Found in the stomach as gastric acid) , Uric Acid C5H4N4O3 (waste product formed as a result of purine breakdown, excreted through urine)
(Uric Acid (Blood) - Health Encyclopedia - University of Rochester Medical Center 2023)
Food: Citric acid C₆H₈O₇ (can be found in Citrus fruits such as lemons and limes), Acetic acid CH₃COOH (can be found in vinegar, present in small amounts contributing to the tartness of fruits such as apples) Lactic acid C3H6O3 (found in milk and produced by the fermentation of dairy products like yoghurt ), Tartaric acid C4H6O6 (most abundant in grapes, can be found in cherries, strawberries, peach, pear), Malic acid C4H6O5 (occurs naturally in fruits such as apples and cherries) , Fizzy drinks (contain carbonic acid H₂CO₃)
Natural sources: Acid rain ( burnt fossil fuels release sulphur dioxide and nitrogen oxides into the atmosphere, when these react with water, oxygen, and other substances they form Nitric Acid HNO₃ and Sulfuric Acid H₂SO₄ respectively), Acidification of natural water (Carbonic Acid H₂CO₃ caused by the disolution of Carbon Dioxide CO2 from the atmosphere with water)
(Ocean acidification 2023) (Nunez 2019)
Different bases:
Sodium Hydroxide NaOH, Potassium Hydroxide KOH, Calcium Hydroxide Ca(OH)₂
Alkalis:
A base that neutralises an acid and is soluble in water is an alkali.
(All alkali are bases but all bases are not alkali. 2019)
How can acidity be measured?
Acid-Base Titration: The acidity of a solution is measured by determining the amount of titrant (standard solution) is required to neutralise the acid. (Determination of food acidity n.d.) In the procedure, a known concentration solution is asses to the acid until reaching endpoint which is indicated visually by a pH indicator solution.
pH strip/indicator paper: pH paper is made of Litmus paper which is coated with an organic indicator that reacts and transitions in colour in presence of hydrogen ions in the solution. (seotechwriter 2022) This method cannot often obtain accurate results like a pH meter as pH papers are not designed to measure extreme pH values and cannot provide precise pH values but only general indications. (pH Meter Vs pH Paper: Which one do you need? | Atlas Scientific 2021)
Dissociation:
Dissociation is the process in which an acid breaks into ions when dissolved in water. (Shiken 2023)
What factors determine acidity of a solution:
pH: Acidity is measured commonly on the pH scale ranging from 0-14 pH. 7 pH is neutral, less than 7 pH is considered acidic whilst pH values above 7 are basic.
(pH Scale | U.S. Geological Survey 2019)
Hydrogen ion (H+) concentration: Higher concentrations of hydrogen ions result in higher acidity of a solution (measured by pH)
pH meter: The glass electrode inside the pH probe measures the pH by comparing the difference in the voltages of hydrogen ions produced between the sample solution (unknown pH) to a 'buffer' solution (reference solution with defined pH levels).
(pH Meter - Instrument - Holme Research Group - Iowa State University 2023)
In order to obtain accurate results it is important to calibrate before usage by measuring solutions with a known pH value. (pH Meter Vs pH Paper: Which one do you need? | Atlas Scientific 2021)
pH indicator solutions: These solutions change colour in response to varying pH levels, when added to a solution it reactions with the hydrogen ions present. They provide a visual approach to observe shits in pH ranges. (Used in titration to determine the endpoint/equivalence point of the reaction between an acid and the base) An high degree of accuracy cannot be expected as it is prone to many errors such as temperature. (Ways of Measuring pH 2023)
Red Cabbage juice: This can be used as a natural pH indicator to determine acidity based upon the colour it changes varying on the pH of the solution. Red cabbage juice can be used as a pH indicator, by mixing the chosen solution with the cabbage juice. Red or Pink colour indicates an acid whilist green or yellow indicated a base, if the solution is neutral it will remain purple.
(Red Cabbage Indicator - American Chemical Society 2023)
It is a fairly accurate indicator to cost efficiently test household items for acidity levels, although it is not as accurate in comparison to other available indicators. Disadvantages include its contamination in the solution, inability to obtain acidic or basic strength and inability to observe changes for solution which are opaque/darker in colour (John 2021)
Common pH indicator solutions: Methyl orange (Red Acidic colour), Bromothymol blue (Yellow Acidic colour), Phenolphthalein (Colourless acidic colour)
(Module 6: Acid/base Reactions: pH Indicators – HSC Chemistry 2019)
Possible investigation design: Measuring the acidity of various concentrations of household items (lemon juice, vinegar, orange juice, cleaning products such as glass cleaner)
Testable question: How does varying concentrations of Vinegar affect the colour change of the indicator? ( This question investigates the relationship between concentration and its impact on acidity)
Testable hypothesis: If the concentration of Vinegar is increased, the red cabbage indicator will shift to darker shades of pink.
IV: The concentrations of Vinegar (ie. 10%, 25%, 50%, 100%) DV: The colour change of the red cabbage indicator Possible CV: Volume of red cabbage juice indicator, same brand of Vinegar.
Limitations: The red cabbage juice can only provide general indication of acidity, ensuring the dilution of vinegar is accurate through all concentrations can be difficult and can result in result variability
Possible investigation design: Measuring the acidity of varying amounts of household items (ie, lemon juice, vinegar, orange juice, cleaning products such as glass cleaner) .
Testable question: How does the amount of lemon juice used affect the pH levels of the solution.
Testable hypothesis: If the amount of lemon juice is increased there will be a lower pH level in the solution.
IV: The amount of lemon juice used (ie. 5mL, 10mL, 15mL, 20mL) DV: pH level of the solution Possible CV: The brand of lemon juice used, pH paper
Limitations: Variation in the accuracy when measuring the amount of lemon juice used
Possible findings: That increasing the amount of lemon juice used may result in a more acidic solution.
Possible investigation design: Testing various temperatures of soda to investigate the impact on acidity. (ie. Sprite, Fanta, Cola, Solo)
Testable question: Does the storage temperature of sodas affect their acidity levels?
Testable hypothesis: Storing sodas in higher (warmer) temperatures will have higher acidity levels than lower (colder) temperatures.
IV: The storage temperatures of soda (ie. 3°C refrigerator temp, 15°C, 25°C room temp, 35°C warmer temp) DV: Acidity level of the soda Possible CV: The brand of cola used, type of soda used, period of storage.
Limitations: Different brands/types of sodas may require different temperature conditions meaning that the results cannot be generalised.
Possible findings: That storing sodas at lower temperatures in comparison to higher temperatures will have higher acidity levels.
IV: In acid base titration the independent variable is the volume of titrant (acid or base of known concentration. i.e. sodium carbonate Na2CO3) DV: The volume of acid solution (ie. hydrochloric acid HCL) needed to reach endpoint of titration. CV: The equipment used (i.e. pipette, burette, conical flask) , The volume and concentration of the titrant and the vole and concentration of the acid solution, the indicator (i.e. Methyl Orange)