Chemistry in a Shopping Trolley. Ascorbic acid Concentrations of fresh orange, fresh lemon, store-bought orange juice, store-bought lemon juice and a Berocca tablet

Scientific Study 2016 23 Pages

Chemistry - Food Chemistry



1.0 Abstract

2.0 Introduction

3.0 Body
3.1 Acids and Bases
3.2 Le Chatelier’s Principle
3.3 Titrations
3.4 Ascorbic acid
3.5 Secondary Experiment

4.0 Experiment
4.1 Aim
4.2 Hypothesis
4.3 Justification of hypothesis
4.4 Materials
4.5 Methodology
4.6 Experiment Set-up
4.7 Results

5.0 Discussion

6.0 Recommendations

7.0 Conclusion

8.0 Bibliography

9.0 Appendix

1.0 Abstract

The concentration of Ascorbic acid in lemons, oranges, lemon juice, orange juice and a Berocca tablet were calculated to determine the best way to receive the recommended daily intake of Ascorbic acid. This experiment was conducted to decide the best source of Ascorbic acid for pregnant women, which is available from a supermarket. The concentrations were finalised by titrating the five substances and then calculating the concentration of Ascorbic acid. It was found that lemons had the highest concentration of Ascorbic acid, which was 0.6175mol/L. The fresh lemon was followed by the Berocca tablet, which had a concentration of 0.585mol/L, lemon juice with 0.5625mol/L, orange with 0.105mol/L, and finally orange juice, which had 0.095mol/L. While the lemon had the highest concentration, it was decided that fresh oranges were the best source of Ascorbic acid for pregnant women. These findings are significant because many pregnant women do not receive the recommended daily intake of Ascorbic acid, which has detrimental health impacts on themselves, and their child.

2.0 Introduction

This task will undertake an experiment to determine and compare the concentration of Ascorbic acid in lemon, orange, lemon juice, orange juice and Berocca tablets to predict the best method for pregnant women to receive the recommended daily Ascorbic acid intake. Some commonly known sources of Ascorbic acid, more commonly known as Vitamin C, are natural orange juice, natural lemon juice, store-bought orange juice, store-bought lemon juice, and Berocca tablets. With the large variety of products claiming to contain the highly sought-after chemical Ascorbic acid, there are many misconceptions as to which products contain the highest concentration and the most cost-effective and beneficial to the human body. The experiment will be conducted to determine the best method for Ascorbic acid consumption during pregnancy.

3.0 Body

3.1 Acids and Bases

All substances are classified as either an acid or base, according to the three theories of acids and bases by Arrhenius, Brønsted-Lowry and Lewis. In the Arrhenius Theory of acids and bases, “Acids are substances which produce hydrogen ions in solution” and “bases are substances which product hydroxide ions in solution” (Clark, 2002). The process of neutralisation occurs when hydrogen ions and hydroxide are involved in a chemical reaction; in this reaction an acid and a base is mixed together. The product of this reaction is water and a salt. This chemical reaction is shown below:

Neutralisation according to Arrhenius’ Theory

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Example of Neutralisation Reaction

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(Study.com, 2016).

Strong and Weak Acids/Bases

The acidity and basicity of substances are determined by a pH Scale, which is numbered from 0 to 14, where substances ranked at 0 are extremely acidic, substances ranked at 14 are extremely basic, and substances ranked at 7 are neutral. Neutral substances are neither acidic, nor basic; examples of neutral substances are pure water and blood. The dissociation of ions in the solution determines the strength of the acid and base; for instance, an acid that has completely dissociated ions is referred to as a strong acid, meaning it is extremely acidic and appears towards the acidic end of the pH Scale. On the contrary, a basic substance that has only partially dissociated ions is referred to as a weak base, meaning it is not extremely basic and appears towards the neutral (middle) range of the pH Scale (Elmhurst College, 2003).

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1: pH of Common Substances

Properties of Acids

According to the Arrhenius definition of acids and bases, there are different properties, which assist in determining whether substances are acidic or basic. The property already established in the Arrhenius Theory is the release of hydrogen ions into water (aqueous) solution, which classifies a substance as an acid. The Theory also states that acids neutralise bases in a neutralisation reaction; in this reaction the hydrogen ions of the acid and the hydroxide ions of the base combine to provide water and a salt as the product. Another distinctive property of acids is the result of testing the acidity of a substance with Litmus paper. When a sample of an acid is placed on Litmus paper, the paper transforms from blue to red, indicating that the substance is in fact an acid. The final property of acids is their sour taste; while many acids cannot be consumed due to their toxicity, humans can consume some weak acids, which provides a sour sensation to the taste buds (Chemtutor, 2013).

Arrhenius Acid Equation

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Properties of Bases

Arrhenius also outlined the properties of bases in his Theory, which are still recognised and utilised today to identify basic substances. Arrhenius stated, “Bases release a hydroxide ion into water solution. Oppositely to the acidic properties outlined by Arrhenius, bases neutralise acids in neutralisation reactions, until a point of equilibrium is reached. Bases denature proteins, which explains the slippery textures of strong bases, such as cleaning products. As mentioned with the properties of acids, the basicity of substances can also be measured with litmus paper, but in the presence of a base, the litmus paper will change from red to blue, which is the opposite reaction of an acid. While very few food materials are basic and unfit for human consumption, bases have a distinctly bitter taste, unlike acids, which were stated to taste sour (Chemtutor, 2013).

Arrhenius Base Equation

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Brønsted-Lowry Theory of Acids and Bases

In the Brønsted-Lowry Theory of acids and bases, “An acid is a proton (hydrogen ion) donor” and “A base is a proton (hydrogen ion) acceptor” (Clarke, 2002). This theory involved conjugate acid-base pairs, which are “Two molecular species that easily transfer a hydrogen ion between them, especially from the acid to the base” (Dictionary.com). Brønsted-Lowry also discovered that substances could be amphoteric, meaning that they may act as an acid or a base in chemical reactions, as shown by the following reaction:

Amphoteric Substance

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Brønsted-Lowry Equation

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(Chemed, 2016)

Lewis Theory of Acids and Bases

The third commonly recognised Theory of acids and bases is attributed to Lewis. Lewis stated that “An acid is an electron pair acceptor” and “A base is an electron pair donor” (Clarke, 2002).

Lewis acid-base Reaction

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(Slideplayer, n.d.)

3.2 Le Chatelier’s Principle

Neutralisation reactions occur when the concentration of an acid equalises the concentration of a base in an aqueous solution. Sometimes, a larger amount of acid or base is required in a neutralisation reaction if one of the substances has a higher or lower concentration than the other. The product of a neutralisation reaction is water and a salt, which indicates when the solution has reached chemical equilibrium. There is a chemical equilibrium “when the concentrations of reactants and products are in an unchanging ratio. Another way of saying this is that a system is in equilibrium when the forward and reverse reactions occur at equal rate” (Chemicool, 2014). This definition is supported is Le Chatelier’s Principle, which was published in 1884 by French chemist and engineer Henry-Louis Le Chatelier.

Le Chatelier’s Principle states, “A change in one of the variables that describe a system at equilibrium produces a shift in the position of the equilibrium that counteracts the effect of this change” (Chemed, 2016). The focus of Le Chatelier’s Principle is the activities that a system undertakes when it temporarily shifts away from chemical equilibrium in order to return to its state of equilibrium. The three possibilities for a system to return to an equilibrium state, as explored by Le Chatelier were to alter the concentration of a component in the reaction, alter the pressure applied to a system, or to modify the temperature in which the reaction occurs. A system may be required to implement any of these strategies if the concentration of acid (or base) in a solution exceeds the concentration of base (or acid). For example, in Le Chatelier’s Principle, when more H+ ions are produced by the acid, they will be neutralised by the same amount of base to reach equilibrium (Bhullar, 2016).

3.3 Titrations

“Titration is a general class of experiment where a known property of one solution is used to infer an unknown property of another solution” (Sparknotes, 2016). In a Titration setup, a Buret containing a base of known concentration is suspended above a flask or beaker containing an acid of unknown concentration. A stopcock is sealed at the bottom of the Buret to control the pressure of the base being released into the flask or beaker. The basic setup of a Titration is shown in the below diagram:

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2: Titration Setup

There are two methods commonly used to determine when an acid has been titrated. The first method utilised a pH meter, which is placed in the acid on the unknown concentration. The base is gradually added to the acid until the pH reads exactly 7, which is known to be neutral on the pH scale. When this pH is achieved, the solution is no longer an acid, but it is not a base either; it is a salt in an aqueous solution. The second method involves an indicator, such as Phenolphthalein, which “is an acid or base whose conjugate acid or conjugate base has a colour different from that of the original compound” (Sparknotes, 2016). The first method is more effective because the exact point can be found exactly, but with the second method, the end point is likely to be missed.



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ISBN (Book)
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Chemistry Ascorbic acid Vitamin C Pregnancy Food Drink Lemon Orange Lemon juice Orange juice Berocca Acid Base Titration Reaction



Title: Chemistry in a Shopping Trolley. Ascorbic acid Concentrations of fresh orange, fresh lemon, store-bought orange juice, store-bought lemon juice and a Berocca tablet