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Surname and Initials: DITSHEGO W.
Student number: 219004243
Module: BIOCHEMISTRY 1B REPORT : Ph and making solutions
EXPERIMENT 4
Determination of pH from Vinegar, Sprite, Lemon juice and Bleach through indicators.
Testing pH levels of Vinegar, Sprite, Lemon juice and Bleach.
Abstract:
Introduction:
pH measurement details the concentration of hydrogen ion or hydroxide ion in a solution. A solution
that contains more hydrogen ions in comparison to hydroxide ions is referred to as acidic, while a
solution that contains more hydroxide ion in comparison to hydrogen ions is referred as basic(). Ph
of a solution can be measured in significant amount of ways, the most tradition way include the use
of a ph scale, which comprises of indicator reagents that are introduced into a solution to prompt a
colour change, each colour change is used to rank how acidic or basic that solution is().The Acidic
side ranges from 0 - <7 and basic side from 7> - 14 from pH scale. The substance is regarded neutral
when its pH value is at 7. According to ( Camoes et al.,2011) pH of a either solution is calculated
from the concentrations of that solution. ( Camoes et al, 2011), States again that is it calculated with
the formula pH= -log[ H^+], where H+ the concentration in moles per litre. pH is regarded unitless
since it is expressed in terms of logarithmic form.( Camargos et al, 2018) states that if given the
concentration of hydroxide ion, in order to calculate the pH of a solution, it is needed to find the
concentration of hydronium ion from the formula pH= [H+] +[OH-]=1.0x10^-14, Then determine the
pH once got the concentration of hydronium ion. ( Camargos et al.,2018) states that pH can also be
determined from using the Henderson-Hasselbalch equation which is expressed as pH= pKa + log([A] / [HA]) , this determines the pH of a buffer solution. Substance that are too acidic can be hard to
work with as they may be corrosive and cause chemical burn, in this way It is important to know pH
of substances that you are working with().according to ( Chen et al, 2020) pH level are essential in
the biological and biochemistry as the functioning of our body is largely regulated by cells which
comprises of proteins that are susceptible to pH changes, pH that are not optimal to the pH change
can denature proteins and cause them to dysfunction and this can lead to diseases/disorders,
enzymes are also proteins and their activity may also be affected by different pH level. Chen et
al,2020) states that results in pH level being incorrect can lead to living organisms dying or either not
surviving and if pH level of blood is not balanced , it has caused by not working of kidneys and lungs
and this faulty may lead to certain medical disorders named as alkalosis and acidosis. The cell in our
body has to sustain alkalinity in order for good functioning of body, acidity form may result into
shortage of oxygen at cellular level.
Materials and methods
Preparation of solutions
Laboratory 24-well microtiter plate was firstly prepared and placed on the lab bench, together with
plastic Pasteur pipettes, household liquids that were to be tested and indicators. Pipette was used to
measure 0.5ml of lemon juice and poured five times into the first five blocks of24- well. Bleach was
taken from the bench and measured 0.5ml by pipette and poured into the second five blocks of well.
The third solution, Sprite was taken and measured 0.5ml through pipette and poured into the third
five blocks of24- well. The last solution, vinegar was taken and measured 0.5ml by pipette and
poured into the fourth five blocks of well.
Addition of indicators
Pipette was used to measure 0.5ml bromocresol purple indicator and poured into the first block of
each of the four solutions, and colour change of each solution containing indicator was noted and
recorded into the table after addition of indicator. Pipette was also used to measure 0.5ml of the
bromophenol blue indicator and poured into second four blocks of each of the solutions ( sprite,
bleach, Lemon juice and vinegar) and colour was noted and recorded in the table 1. The amount of
0.5ml of methyl blue was measured by pipette and poured into the third blocks of the solutions and
colour change was noted and recorded. Pipette was used to measure 0.5ml of the phenol red
indicator and poured into the fourth four blocks of each of the solutions and colour change was
observed and recorded into the table. The amount of 0.5ml of the last indicator naphthalene black
was measured by pipette and poured into the remaining blocks containing the solutions( vinegar,
lemon juice, bleach, and sprite), and colour change was observed and recorded into table 1. The pH
range for different liquids was determined using table 2.
Results
Table 1: Variances in colour changes of solutions when added with different types of indicators.
Indicator
Solutions
Lemon juice
Bleach
Sprite
Vinegar
Dark red
Dark purple
Dark purple
Dark purple
yellow
Light pink
Pink
Pink
Methyl blue
Dark blue
Dark orange
yellow
Red
Phenol red
Orange
Red
Red
Red
naphthalene
Black
Black
Black
Black
pH range
3.0-4.7
6.8-8.2
3.0-4.7
5.2-6.8
Acidic or Basic
Acidic
Basic
Acidic
Acidic
Bromocresol
purple
Bromophenol
blue
black
Discussion
Indicators in Lemon juice.
How the indicators work and effect of addition of 0.1M NaOH
According to (), acid base indicator are weak acid/base that are in equilibrium, every shift in their
equilibrium will results in a colour change, i.e. if bromocresol purple is purple this means its in a
basic form, any addition of an acid shift the equilibrium and force a colour change, while any
addition of a base will make the solution remain purple. According () the addition of base in the
preparation of an indicator causes the release OH^- ions into the solution, and this results in all the
indicator to be in their basic form, additionally this effect shifts equilibrium far away from the acid
side as according to () NaOH is a strong base, meaning more hydrogen ions will be required to undo
the change caused by NaOH.
Table 1 shows results of different indicators that were added in solutions of the household liquids.
According to () lemon juice it’s a solution that contain citric acid, which makes it acidic, when
Bromocresol purple was added the colour of the solution become dark red, this colour was not
expected, as the expected colour was yellow, according to Penniston et al (2008) citric acid is a weak
acid, in this way it does not dissociate completely, hence the colour didn’t change to yellow. The
hydrogen ion that was released by citric acid in the lemon juice due to its partial ionization were not
enough to shift the equilibrium change that was caused by 0.1M NaOH thus no yellow colour
formation. The addition of methyl blue resulted deep blue colour resulted also in the same colour
deep blue as expected. The addition of a basic form(pinky) phenol red in lemon juice resulted in an
orange colour formation. Orange it’s a transition colour, which indicate that the equilibrium was
shifting toward the acid side. When naphthalene black was added into the lemon juice, the colour
changed to pure black, the basic form of naphthalene is brown, while the acid form is colourless. In
this way the citric acid solution was not able to protonate the indicator molecules to promote a
colour change that was expected, and this is attributed to the fact the citric acid is a weak base.
Indicators In Bleach
According to () bleach is a detergent, commonly used for stain removal and it has a chemical called
Sodium hypochlorite which makes it basic. All the indicators used were also prepared in a strong
base 0.1M NaOH, this changes the indicators to take their basic form. According to Benzoni and
Hatcher (2001) bleach has a pH at around 11. The addition Bromocresol purple did not cause any
colour change, as a basic form indicator was added into a base. Bromophenol blue addition resulted
in a pink colour change, which it was totally unexpected, as the expected colour was for the solution
to remain blue. Methyl blue addition resulted into an orange colour change, this colour does not
indicate anything about the pH range of bleach, as the acid range colour change must be deep blue
while basic form is blue. Phenol red did not have any colour change, it’s the expected colour change
was purple, showing that the pH range of bleach may be from 6.8 (purple) to 14. When
Bromophenol blue was added into a bleach solution the colour change that arose was light pink,
which is not within the expected colours. Methyl blue gave a dark orange colour after its addition,
the expected colour change was deep blue(base). Phenol red addition had no apparent change, the
colour remained the same after its addition, and the was no expected colour change as the basic
form of phenol red is red and it was added into a base. naphthalene blue has a brown colour in its
basic form, the colour of its addition was black.
Indicators In Sprite
According to Reddy et al (2016) the sprite has a pH of 3.3 as it contains citric acid, which makes the
solution acidic, when a basic form Bromocresol purple was added, a purplish colour arose, which
indicated that it was still basic after the addition as yellow indicates acidity, this is largely due to the
0.1M NaOH that it was the indicator was prepared with as it’s a strong base. Bromophenol blue gave
out a pink colour, which it was not expected, the solution was expected to remain blue. Methyl blue
resulted in the solution colour being yellow, which was not the expected colour, no colour change
was expected as citric acid is a weak base. Phenol red after its addition, the solution was red which
falls under the transitional area of 6.8 to 8.2, the addition of naphthalene black didn’t give any
apparent colour change.
Indicator in vinegar.
According to Xia et al (2020), vinegar is acidic as it contains acetic acid, which is a weak acid as it
does not ionize completely, the addition of Bromocresol purple resulted in a dark purple colour
which indicates the solution is still basic due to the 0.1M NaOH. the addition of Bromophenol blue
gave a pink colour, which was not expected, the expected colours blue(base). Methyl blue indicator
resulted in a solution that was red, this colour does not indicate any PpH range as deep blue
represents the acidic form of the indicator while blue represent the basic form. Phenol red also
resulted in a red colour, which falls under the transitional region of this indicator, and this means
that the pH range of vinegar is 6.8 to 8.2. naphthalene black resulted in a black colour, which
indicates a base form of the indicator.
Conclusion.
The estimated pH ranges were largely influenced by the addition of 0.1M NaOH, the indicator did
not change to colours that allowed for the determination of the pH range on almost all of the
solutions. To improve results it will best to use water in replacement of 0.1M NaOH to that the
equilibrium of the indicators lies not far from each other, in this way any addition of even small acids
may results in a colour change.
References
Assimos D.G, Holmes R.P, Nakada S.Y, and Penniston K.L. (2008).Quantitative assessment of citric
acid in lemon juice and commercially- Available fruit juice products. 22(3) : 567-570.
Camoes M.F, Chen C.T.A, Feistel R., Marion G.M, Millero F.J and Spitzer P.(2011). pH of Seawater.
Meaurement of Ph: Definition, Standards and Procedures. 128(1-4).p 89-96.
Camargos T.P.L, Ferreira R.A.M, Maia T.A.C, Porto M.P and Pottie D.L.F. ( 2018). The pH concepts.
Experimental study of a Ph-CAES system: Proof of concept. Vol-165: p 630-638.
Chen X, Gao L, Lin X, Shaung E, Wang J, and Zheng A. (2020). Intracellular pH. Real-time monitoring
of intracellular ph in live cells with fluorescent ionic liquid. Vol 1111: p 132-138.