Analysis of Acidic Contents of Vinegar | Experiment

Introduction

Vinegar is an acetic liquid produced from the oxidation of ethanol (C2H5OH) by acetic acid bacteria. Astonishingly, traces of vinegar have been found in Egyptian urns dating as far back as 3000 BC. However today, vinegar is commercially available to the public where it is predominately used in food preparation, particularly in the process of pickling (preserving food), vinaigrettes and other salad dressings.

As elucidated above, vinegar is the product of the fermentation of ethanol. This fermentation involves the conversion of carbohydrates to alcohols, carbon dioxide or organic acids using yeasts or bacteria, under anaerobic conditions. When alcoholic solutions containing ethanol less than 18% (CH3CH2OH) are oxidized by Acetobacter aceti (microorganism in the air) bacteria, vinegar (CH3CO2H) is produced.

In the above equation, [O] is the notation for any oxidizing agent, which thus denotes to the acetobacter aceti being used. Typically, the ethanoic acid content will vary from 5-8% in Table Vinegars to approximately 18% in Pickling Vinegars. Depending on what the vinegar is derived from, the acidity or ethanoic content of the vinegar varies, which has consequently manufactured numerous variety of Vinegar.

Table 1, below illustrates information regarding various types of ‘table vinegars’.

Type of Vinegar: Apple Cider

How it is Made: Made from the fermentation of cider or apple must.

% Acidity: 5-6

–

Type of Vinegar: Malt

How it is Made: Made by malting barley, causing the starch in the grain to turn to maltose. Then an ale is brewed from the maltose and allowed to turn into vinegar

% Acidity: 5-10

–

Type of Vinegar: Wine (White, Red, Sherry, sparkling)

How it is Made: The ethanol in the wine is fermented by yeast, producing acetic acid.

% Acidity: 4-7

–

Type of Vinegar: Fruit

How it is Made: Often made from raspberries, blueberries or blackberries, where carbohydrates in the fruit (glucose) are split up to form molecules of ethanol and thus fermentation can take place.

% Acidity: 5-8

Table 1: information on various types of ‘table vinegars’

(http://www.apple-cider-vinegar-benefits.com/properties-of-vinegar.html)

As mentioned, the production of vinegar yields its key and fundamental component, ethanoic acid (CH3COOH). Ethanoic acid or acetic acid, is a simple organic acid belonging to the group of carboxylic acids; organic compounds with a – COOH functional moiety. Acetic acid is considered a weak acid, in that it is monoprotic, partially dissociated acid in an aqueous solution.

In Figure 2 to the left, the hydrogen (H) atom in the carboxyl group (- COOH) in acetic acid usually is discharged as an H+ ion. The strength of an acid refers to its tendency to lose a proton. Therefore the discharging of this H+ ion (proton) as a result, gives an acetic acid its acidic property. As mentioned earlier, there a different types of vinegars, two of these being; white wine vinegar and apple cider vinegar.

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White Wine Vinegar

White wine vinegar, is manufactured from allowing a distilled alcohol (i.e. any selected blend of white wine) to undergo acidic fermentation. Oxygen (O) combines with ethanol molecules, thus reducing its atomic content in the process. As a result of this distilled alcohol being oxidized, the chemical component, as mentioned changes, where the white wine converts to a sour, reasonably unpleasant vinegar.

Apple Cider Vinegar

Apple cider vinegar is created through a two step process involving micro-organisms. The first step involves the fermentation process, where the glucose (C6H1206) present in the juices of the apple juice is converted into ethanol by yeast. This is shown in figure 3 to the left and is further analysed in the appendix on Page sjhd.

In the second step; Acetobacter, a form of aerobic bacteria oxidizes the ethanol molecules formed by fermentation into acetic acid (apple cider vinegar) and a by-product of water. The equation involving the second step of producing apple-cider vinegar is shown below, in figure 4 to the right.

Quality Control

Quality control is a process employed to ensure a certain level of quality in a product or service. It may entail any procedures a business/company deems necessary to provide the control and verification of a certain characteristic of a product or service. “The chief concept of quality control is to ensure that products, services or processes provided meet specific requirements and are dependable, satisfactory, and fiscally sound”.

In essence, it involves the examination of a product, service, or process for certain minimum levels of quality. Quality control attempts to identify products or services that do not meet the company’s and governments for that matter, specified standards of quality. Anything that may be purchased by the general public has undergone quality control. From the food we eat to the technology we use, quality control procedures have been carried out, in order to ensure the safety and efficiency of the product.

The quality control of vinegar regards to strength or pH of the vinegar. This therefore, refers to the ethanoic or acetic acid content in the vinegar. At the retail level, as mandated by the U.S. Food & Drug Administration (FDA), all vinegars sold in the United States must be at least 4% acidity. This regulation of the acidity in vinegars (at least 4% acidity) also applies to the retail level of Australia.

However, in the case of white wine vinegars, the acidity must be at least 4% acidity and no more than 7% acidity. Cider vinegars (i.e. apple) tend to be slightly more acidic than white wine vinegars with approximately 5-6% acidity. It has been investigated that both white wine vinegars and cider vinegars are most effective (optimal) in terms of pickling and taste, regarding vinaigrettes and salad dressings, with a pH from 5.5 to 6.5%.

All vinegars are not legalized to have an acidity which is below 4%, as the vinegar becomes ineffective for use in pickling (a process of preserving food by anaerobic fermentation). White wine vinegars which have an acidity of above 7% may prove to be an irritant to the stomach.

Also, in the process of manufacturing the vinegars, the growing of acetobacters, requires a relative amount of vigilance. Therefore, quality control is carried out specifically in vinegar factories which regard conditions (i.e. no oxygen etc) that enables the bacteria to perform most efficiently.

The Experimental Investigation

Throughout this report, titrimetric analysis will be used in determining the percentage by mass of the acetic acid (CH3COOH) content in various vinegars. Titration is a type of volumetric analysis and for this particular investigation a measured quantity of vinegar (volume) is titrated to the phenolphthalein endpoint using a measured volume of diluted standardized sodium hydroxide solution (NaOH) – the titrant. The set-up of this acid-base titration is seen in figure 5 to the right.

As a result, the acid-base reaction between the vinegar (CH3COOH) and Sodium Hydroxide (NaOH) creates the products of water and a salt (neutralisation). This neutralisation reaction is seen below in figure 6;

After obtaining valid results of the volume of NaOH needed for the endpoint to be reached (titre), several calculations can be thus carried out, which will enable the calculation of the percentage content of acetic acid in various white wines. Stepped calculations involving acetic acid content will be illustrated in the analysis of the report.

As well as performing experimentation which enables the calculating of acetic acid content (percent by mass) in three commercially available white wine vinegars, this investigation will also encompass the manufacturing of an apple cider vinegar and methods performed to investigate the progression of the acetic acid content in this vinegar over a period of 5 days, while it ferments. The purpose of this will be to investigate the acetic acid content (% acidity) of the apple cider vinegar relative the time elapsed during fermentation. Intrinsic to this study, the standardization of sodium hydroxide solution (NaOH) will also be performed.

Aims

White Wine Vinegar Investigation

To investigate the acetic acid content (percentage by mass) of various white vinegars and compare these results to that of the published data labelled on each white wine vinegar bottle.

Homemade Apple Cider Vinegar

To investigate the acetic acid content (percentage by mass) of a homemade apple cider vinegar, relative to its fermentation over a 5 day period.

Hypotheses

White Wine Vinegar Investigation

If the sources of error carried out during the acid-base titrations are kept at a minimal, then the results of the acetic acid content (percentage by mass) of the various white wine vinegars produced from the experiment should be reasonable similar to that of the published data for each white wine vinegar.

Homemade Apple Cider Vinegar

If the homemade apple cider vinegar is correctly produced thus allowing fermentation to effectively take place, then as a result of the continuos fermentation of the apple, the acetic acid content (percentage by mass) will increase over the period of the 5 days.

Materials

Equipment 1: Volumetric Analysis (Titration) of acetic acid in Vinegar/s

• White Wine Vinegars; Coles Italian, Anchor Margret River, Capriccio (see figure 7)
• Homemade apple-cider vinegar
• 5mL graduated cylinder
• 3 x 200mL Beakers
• Distilled Water
• 0.1M Standardized Sodium Hydroxide (NaOH)
• Calibrated Burette
• Phenolphthalein Indicator
• White tile
• Stand with clamp
• Funnel
• Electronic Balance

Figure 7: Coles Italian, Anchor Margret Rive & Capriccio white wine vinegars, Homemade Apple Cider Vinegar

Equipment 2: Preparation of Homemade Vinegars

• Juicer
• ‘Pink Lady’ Apples
• Sugar
• Cooking Pot
• Filtered Water
• Fresh Brewer’s yeast (2 grams)
• Air tight container

Equipment 3: Standardizing of Sodium Hydroxide solution (NaOH)

• * All the equipment from the list of Equipment 1 except vinegars.*
• KHSO4 Solution

Method

Method 1: Volumetric Analysis (Titration) of acetic acid in Vinegar/s

This laboratory procedure will determine the percentage Acetic Acid (CH3CO2H) in multiple commercial white wine vinegars. An aliquot of the white wine (acetic acid) will be titrated against the strong base, 0.1M Sodium Hydroxide (NaOH) and the endpoint of the titration will be detected using a Phenolphthalein indicator.

Safety: Sodium Hydroxide is corrosive. Avoid contact, but if any touches skin, wash it off immediately. Safety glasses are mandatory (refer to appendix for risk assessment).

All the materials were assembled on an allocated laboratory bench.

The 5mL graduated cylinder was weighed using the electronic balance and recorded.

2.5mL of vinegar was measured using a 5mL graduated cylinder

The 5mL graduator cylinder containing the 2.5mL of vinegar was weighed using the electronic balance and recorded. This vinegar was then poured into a 200mL beaker, which was labelled, analyte.

100.0mL of distilled water was then added to the ‘analyte’ beaker.

Several drops of phenolphthalein indicator was added to the analyte beaker

0.1M NaOH solution was then placed in a burette, where this solution was swirled around the burette, ensuring that the NaOH solution came in contact with the entire inside wall of the burette. The NaOH solution was then poured into a beaker labelled ‘titration waste’. Note: this rinsing step was to ensure that any possible acid from previous experiments was not present in the burette.

The burette was then positioned using the stand and g-clamp at a height above the bench which allowed the analyte beaker to be moved easily beneath the tip of the burette.(refer to figure 8)

The burette was then filled with 0.1M NaOH solution using a funnel and the initial volume of the NaOH solution was recorded. The ‘analyte’ beaker was then placed on a white tile directly under the tip of the burette

The stopcock on the beaker was turned such that a slow, small flow of NaOH solution was being poured into the ‘analyte’ beaker, stirring the beaker in the process.

The NaOH titrant was added to the ‘analyte’ beaker drop-by-drop until a half-drop of the NaOH solution caused a permanent pale pink colour change (see figure 9) to the anaylte, where the stopcock was turned, restricting no more flow of the NaOH solution. Note; this is the equivalence point of the titration and it should only take one-half drop for the colour change to persistent.

The final volume of the NaOH solution was recorded.

The solution in the ‘anaylte beaker’ was deposited in a waste beaker, the burette was topped up with NaOH solution and the ‘analyte’ beaker was washed thoroughly using deionised water, in preparation for the next titration

Steps 3 – 13 were repeated at least 6 times for each of the white vinegars. Steps 3 – 13 were repeated at least 3 times for the homemade apple-cider vinegar on each day of the scheduled titration.

b) Dark pink colour solution

The equivalence point of the reaction was detected when the colourless solution changed to a pale pink colour. If the solution turned dark pink, the endpoint had been surpassed.

Method 2: Preparation of Homemade Vinegars

In this experiment, pink lady apples will be prepared in an airtight container (no oxygen) where it will undergo fermentation performed by fresh brewer’s yeast over a period of 5 days (i.e. titration performed each day after the vinegar is made.)

Using the juicer, several ‘pink lady’ apples were crushed.

The apple’s juices and flesh were extracted and placed in a cooking pot.

An equivalent amount of filtered water to that of the juices and flesh was then added into the cooking pot.

The cooking pot was then boiled until the texture of the juices/flesh started to soften.

The juices and flesh were then filtered into a measuring cup and ¼ and sugar was added for every litre of juice filtered.

The liquid was allowed to cool down to room temperature

2 grams of fresh brewer’s yeast was added to the liquid

The mixture was then poured into an airtight container (i.e. no oxygen could enter) and allowed to ferment until the scheduled titration.

Method 3: Standardization of Sodium Hydroxide (NaOH)

KHSO4 will be titrated against NaOH, which would thus enable calculation of the molarity (concentration) of the sodium hydroxide solution used in all titrations of this experiment.

Safety: Sodium Hydroxide is corrosive. Avoid contact, but if any touches skin, wash it off

immediately. Safety glasses are mandatory (refer to appendix for risk assessment).

0.715g of KHSO4 was weighed using the electronic balance and transferred to a 200mL beaker.

The 0.715g of KHSO4 was dissolved in 50mL of deionised water.

Several drops of Phenolphthalein indicator was added to the ‘analyte’ beaker.

The KHSO4 was titrated to the Endpoint using NaOH (steps 7 -12 in method 1). Refer to figure 10 to the right.

Steps 1 – 4 were repeated for a total of 6 trials.

Results

The following information refers to details regarding the three white wine vinegars used for titremetric analysis. These were;

• Capriccio Aged White Wine Vinegar (1L)
• 6 % Acidity
• Purchased Price (Coles Supermarket); $8

Other Information; – Product of Italy

– 100% owned Australian Company

– Ingredients; White vinegar, Antioxidant (224, contains sulphites)

– Some sedimentation is natural + vinegar is made 100% guarantee

• Coles Italian White Wine Vinegar (500mL)
• 6 % Acidity
• Purchased Price (Coles Supermarket); $3

Other Information; – Product of Italy

– Coles Supermarket 800 Toonite Rd, Hawthorn, Eat Victoria

– Storage; cool, dry place

– Best Before; 03/12/2012

– Ingredients; White vinegar, Antioxidant (224, contains sulphites)

• Semillon Sauvignon Bianco White Wine Vinegar (375mL)
• Anchot (since 1854), Margret River
• 6 % Acidity
• Purchased Price (Coles Supermarket); $4.50

Blog on the Bottle – “This unique oak matured white wine vinegar has been crafted from the premium Margret River. The region’s cooling ocean breezes and Mediterranean Climate produce fresh crisp white wines with intense fruit flavours with hints of fig, pear, lime & lemon grass. The fresh intensity of this Margaret River Classic is now preserved with acidity created using traditional methods”

Other Information; – Produce of Australia

• 148 Carrington St, Freemantle WA 6163
• www.anchorforts.com
• Ingredients; Vinegar brewed from Semillon Sauvignon Bianco wine that contains preservation (220)

Analysis

The calculations performed in the appendix on pg ajkh, prove to show that the molarity of the Sodium Hydroxide (NaOH) used in through the titrations is 0.1042 M. This will be the molarity of NaOH which will be used when carrying out calculations involving the percentage by mass of acetic acid content in vinegar.

Calculating the percentage by mass of acetic acid content in vinegar

Below is an example on how to calculate the percentage by mass of acetic acid content in vinegar was carried out. Each procedure in calculating the acetic acid content by mass, is proceeded the same way as shown in the example below, however substituting in appropriate values. All stepped procedures on how each calculation of the percentage by mass of acetic acid content in vinegar has been reached, are shown in the appendix, running from page oreoer. The results of these calculations have been tabulated and summarised in the table kjsds on page sjds.

Capriccio White Wine Vinegar – Product of Italy

Now, as mentioned previously the titrimetric analysis will be used in determining the percentage by mass of acetic acid (CH3COOH) in Capriccio White Wine Vinegar.

As the volume (v) and molar concentration I of the standardized NaOH solution are known, the number of moles (n) of the NaOH can be found.

Therefore, number of moles (n) of NaOH used = Concent. of Stand. NaOH I

x Average titre (v)

Thus, n (NaOH) = Cv

n (NaOH) = (0.1042 M) x (0.0276 L)

n (NaOH) = 0.00288 (R 5DP)

Now, since the Sodium Hydroxide (NaOH) reacts with Acetic Acid (CH3COOH) in a 1:1 molar ratio, as seen from the equation below;

Then, the number of moles (n) of CH3COOH is; 0.00288, as;

n (NaOH) = n (CH3COOH) = 0.00288

Now, the mass (m) of the vinegar (CH3COOH) can be found using the number of moles (n) of CH3COOH and its molecular mass (M).

Since, number of moles (n) of CH3COOH = mass (m) of CH3COOH/molecular mass

(M) of CH3COOH

n = m/M

Therefore, the mass (m) of CH3COOH = number of moles (n) of CH3COOH x molecular

mass (M) of CH3COOH

m = nM

As the number of moles (n) of CH3COOH is 0.00288 and the molecular mass (M) of CH3COOH is, 60.05 g/mol, then;

Mass (m) of CH3COOH = 0.00288 x 60.5

= 0.17424

Finally, the percentage by mass of CH3COOH in vinegar is calculated by;

% by mass of CH3COOH = (mass (g) of CH3COOH / mass (g) of vinegar) x 100

= (0.17424/2.7963) x 100

= 6.23 (Acidity)

Therefore, Capriccio White Wine Vinegar has an acetic acid content of approximately 6.23%.

Vinegar during the 5 days of fermentation

Was Phenolphthalein indicator suitable for this acid-base titration?

For this particular experiment, a Phenolphthalein indicator was used to determine the equivalence point, where a colourless solution turned into a pale pink solution (see figure sdk).

From the calculations performed in the appendix from page dfj to ejre, it showed that the equivalence point of this specific acid-base titration is equal to a pH of 8.72.

For any titration, it is most desired to have the equivalence point equal to the end point. Therefore, for this particular acid-base titration an ideal acid-base indicator would be one that changes colour near the pH of 8.72 (i.e. pH 8.72 is in the range of the indicator).

In the appendix, table sdjds illustrates common acid-base indicators with their respective pH range and colour changes. It is observed from this table, that a phenolphthalein indicator is an ideal and suitable acid-base indicator for this specific titration, as it ranges from pH 8.0 to 9.6. This would therefore and is seen in the experiment for a colour change to occur from a colourless solution to a pale pink solution. This change in GRAPH

Analysis of Results

White Wine Vinegars

Table 6 and 7 summarise the results of the acetic acid content of the three white wine vinegars and the homeade apple cider vinegar.

The acetic acid content (% by mass) of the three white vinegars, that were calculated through titrimetric analysis is graphically represented in figure 11 below.

It is seen from figure 11, that the white wine vinigar which is has the highest acetic acid content and thus most acidic is the Coles Italian White Wine Vinegar. This therefore means that this particular vinegar has the greatest tendency out of the all vinegars to discharge H+ ions (protons). Similarly, Capriccio White wine vinegar proved to be the least acidic which therefore meant that it has a least propensity to loss H+ ions.

From figure 11, it can also be noted that each vinegar satisfies the U.S. Food & Drug Administration (FDA) regulation; that is that the acidity of white wine vinegar must be at least 4% and no more than 7% acidic.

All 3 white wine vinegars, as mentioned in the results on page 11, had ‘6% acidity’ published on the label of each vinegar bottle. Using this ‘6% acidity’ as the theretical result and the results in table 4 as the practical results shown, the percentage error may be calculated as;

Usinf the equation above, the resulting percentage error of the three white wines carried out in this investigation are seen in table 6 below,

Anchor Margaret River White Wine Vinegar proved to contain the least percentage error out of the three white wine vinegars. It is also was also the most expensive vinegar. Similarly, Coles Italian White

Wine Vinegar proved to contain the most percentage error and was the least expensive out of the three. Therefore it can be said the increase in the retail price of white wine vinegar consequently reassures customers of product which has been manufactured under a stricter regimes of quality control.

Apple Cider Vinegar

As seen in table 7, the acetic acid content (% by mass) of the homemade apple cider vinegar increased over the 5 day period. This is graphically represented in figure 12 below;

The graph shown in figure 12, supports the fact that fermentation (conversion of the glucose in the apples to ethanol and then to acetic acid) continued to occur during the entire period of the 5 days. This consequently caused the acidity to increase every day as more acetic acid was thus produced.

Note: Although a common trend in the increase of acetic acid content or acidity of the apple cider vinegar is observed, there was no constant or regulative interval (24 hours) that each titration was performed.

Although apple cider vinegar at days 3, 4 & 5 satisfies the regulations of the FDA’s, apple cider vinegars are most effective (optimal) and thus commercially retailed as a acidity range between 5-6%. Therefore, the vinegar at day 5 would essentially be most appropriate in terms of the acidity of an apple cider vinegar (Note: only suitable regarding acidity).

If more time was allowed, further fermentation would have elapsed, allowing acetic acid content and thus acidity of the apple cider vinegar to increase, however this increase would become slighter (heading towards 6.5 % acidity).

Discussion

Sources of Error

The initial and final volumes of the NaOH solution were recorded to the nearest 0.2mL (calibrated intervals on burette). This volume was interpreted by human perception and therefore would create an error of ± 0.1mL to the reading of the NaOH volume.

When 2.5mL of vinegar was measured using the graduated cylinder, the volume was measured to the nearest 0.2ml (calibrated interval on grad. cyclinder). This as a result would cause an uncertainty of the volume of ± 0.1mL, as human perception was used to judge the volume. This proves to be a significant source of error towards the validity of the result and limiting this error for future procedures is discussed in method refinements.

Human error was carried out consistently throughout this experiment, as volumes were measured according to human perception. Also the fact that there was a difference in human perception among the group (i.e. everyone doing measuring), this would of increased the significance of this source of error.

Even though the contamination in the anaylte or titrant was attempted to not subsist through rinsing of equipment after each trial, there may have been the possibility of contamination, since the same beakers were continuously being used.

Limitations

The method of this experiment enabled the percentage acidity of various vinegars to be calculated. Although vinegar is predominantly made from acetic acid, vinegar also contains tartaric and citric acid. Therefore, the acetic acid content is not equal to the acidity (%) of vinegar. However in saying this, a very minute portion of the vinegar is made up of tartaric and citric acid, such that its there contribution to the acidity of the vinegar is regarded as negligible.

The time allowed to perform titration procedures was approximately 5 days. As a result, white wine vinegar was unable to be manufactured as the white wine fermentation occurs over a period of 3 to 6 months. Therefore, apple cider vinegar was manufactured instead where fermentation is complete, generally after a period of 8 – 10 days.

Method/Procedural Refinements

The measuring of the 2.5mL was imperative in the validity of the result obtained from this experiment. This is significance is seen as there is a wide discrepancy between the resulting titres (see table 2). In order to limit the degree of this source of error, the method should be modified such that 10 or even 25mL of vinegar is initially measured. This would thus produce more valid results than those obtained in this experiment

Members of the group should be assigned to perform specific duties in the method. This would attempt to eradicate the difference in human perception, especially when measuring volumes and thus produce more valid results.

More white wine vinegars or even different types of vinegars can be used to perform titrimetric analysis. This as a result would indicate a clearer and evidential conclusion regarding the acetic acid content (% by mass) of not just white wine vinegars, but vinegar in general.

Was the Hypothesis supported or disproved?

The results produced from this investigation have thus supported both hypotheses involving the white wine vinegar investigation and the homemade apple cider vinegar investigation that were stated earlier, on page 6.

Table 6 supports the white wine vinegar hypothesis, as the results of the acetic acid content of the three vinegars from means of titrimetric analysis were similar to the published acidity on the vinegar’s bottle. This as a result indicates that the sources of error carried out during the acid-base titrations were kept at a minimal.

Furthermore, the results produced from this investigation has supported these two hypothesise.