ENGAGE PHASE
One day, a student drops
in at the stall to get a drink. At the stall, she order orange juice and after
drank she noticed that the orange juice taste sour than usual. So, she wonders
how concentration of orange juice influences its taste and why mostly drink has
different taste. She also thinks how pH can lead to disease like cancer.
EMPOWER PHASE
Introduction
From our group
discussion, we decided to choose experiment that test the pH level of common
drinks using the data logger. The pH data logger that we choose is DrDAQ data
logger. DrDAQ is used here as a pH meter with the addition of a pH probe to
measure the pH level over the entire pH scale of a range of common drinks. Recently
dentists have begun warning about the dangers of drinking acidic drinks. Teenagers,
they suggest, who drink large amounts of fizzy ‘pop’ drinks suffer from tooth
erosion whereby the enamel covering of the tooth is dissolved by the acid in
the drink. Athletes are also at risk from drinking sports drinks. The
recommended ‘safe’ level for the pH of drinks is 5.5, Anything below this can
promote tooth erosion. This experiment looks at the relative pH values of
different drinks and can be used to determine whether a particular drink is
‘safe’ according to the above criteria. It can also be used as a good
introduction to further studies into tooth decay and enamel stripping. It is
suitable for ages 14+ and requires some knowledge of the pH measurement.
Actually, measurement of pH for aqueous solutions can be done with a glass
electrode, pH meter or by using indicator. However, through this experiment to
test pH level in common drink, the method use to measure the level of pH is by
using pH meter by apply DrDAQ as a data logger.
All foods and drinks
have their own pH levels which have risk to affect the pH of human body. In
chemistry, pH is a measure of the activity of the hydrogen ion. More clearly,
pH is the universally accepted scale for the concentration of hydrogen ions in
an aqueous solution. A common drinks pH can be measure either in acidic state,
neutral or alkaline state. An ideal pH is between seven to seven and half on
the scale from one to 14. The human body can functions optimally at alkaline
conditions which is about at pH 7.4. It is necessary to maintain a healthy pH
level to make sure there is not too much acid interferes with our blood cells
that have ability to transport oxygen.
Drinking certain
beverages also can increase our pH level. So that DrDAQ is used as a meter with
the addition of a pH probe to measure the pH level in the common drinks such as
orange juice and apple juice. Orange juice is one of the famous juices among
the others in this world. This is according to the Drink Secrets website.
Recently, dentists have begun warning about the dangers of drinking acidic
drinks. Teenagers, they suggest, who drink large amounts of fizzy ‘pop’ drinks
suffer from tooth erosion whereby the enamel that covering the tooth is
dissolved by the acid in the drink. Moreover, athletes also face the same
problem and have to take risk because they drinking sports drink.
This experiment looks at
the relative pH values of different kinds and can be used to determine whether
a particular drink is safe according to the criteria that had been stated.
Moreover, it is also can be used as a good introduction to further studies into
tooth decay and enamel stripping. Furthermore, it is also introduction for
using data logging that can operate independently of a computer unlike many
other types of data acquisition devices. Moreover, data loggers more powerful
programmable devices which are capable of handling hundreds of inputs.
A data logger is an
attractive alternative to either a recorder or data acquisition system in many
applications. When compared to a recorder, data loggers have the ability to
accept a greater number of input channels, with better resolution and accuracy.
Also, data loggers usually have some form of on-board intelligence, which provides
the user with diverse capabilities. For example, raw data can be analyzed to
give flow rates, differential temperatures, and other interpreted data that
otherwise would require manual analysis by the operator.
The major difference
between a data logger and a recorder, however, is the way the data itself is
stored, analyzed and recorded. A common recorder accepts an input, and compares
it to a full scale value. The pen arm is then deflected across the recording
width, to produce the appropriate ratio of the actual input to the full scale input.
For example, using a recorder with a 1 Volt full scale, an input of 0.5 Volts
would move the pen 0.5/1 or 50% of the distance across the recording width. In
comparison, a data logger accepts an input which is fed into an
analog-to-digital converter prior to analysis and storage. This method has advantages
in accuracy and resolution, while only a recorder can provide a truly
continuous trend recording. Data loggers can also offer advantages over
dedicated, computer interface systems. A data logger is a self contained unit, which
does not require a host to operate. It can be installed in almost any location,
and left to operate unattended. Data loggers have a distinct advantage over
conventional interface devices, in that they operate in this stand-alone mode,
and yet have the capability to “dump” or transfer the data to a host system, if
required. Most data loggers have the ability to work similarly to standard
recorders, in that they provide the user with a hard copy printout of the data
recorded. This data can be immediately analyzed for trends, or stored for
historical archive purposes. Data loggers can also monitor for alarm
conditions, while recording a minimum number of samples, for economy. If the
recording is of a stead-state nature, without rapid changes, the user may go
through rolls of paper, without seeing a single change in the input. A data
logger can record at very long intervals, saving paper, and can note when an
alarm condition is occurring. When this happens, the event will be recorded and
any outputs will be activated, even if the event occurs in between sample times.
A record of all significant conditions and events is generated using a minimum
of recording hardcopy.
The differences between
various data loggers are based on the way that data is recorded and stored. The
basic difference between the two data logger types is that one type allows the
data to be stored in a memory, to be retrieved at a later time, while the other
type automatically records the data on paper, for immediate viewing and
analysis. Many data loggers combine these two functions, usually unequally,
with the emphasis on either the ability to transfer the data or to provide a printout
of it. The example of data loggers are temperature, flow and level, pH and
conductivity, data acquisition, pressure, strain and force, and heaters. Each
data logger can be use in many experiments such as air velocity indicators,
doppler flowmeters, level measurement, magnetic flowmeters, environmental
instrumentation, pH electrodes and instruments, water and soil analysis instrumentation.
Equipment required
1.
DrDAQ data logger connected to a PC
2.
One pH sensor (DrDAQ Part no DD011)
3.
Containers for the drinks (we used plastic drinking cups)
4.
A selection of common drinks - we used:
a)
Orange Juice
b)
Apple Juice
c)
Black Coffee
d)
Black Tea
e)
Lemon Tea
f)
Original Coke
g)
Pepsi
h)
Cherry Coke
i)
Ribena
j)
Lemon Squash
k)
Milk
Experiment set up
1.
Fill all cups with an equal amount of liquid which will cover
the pH probe tip.
2.
Mark the cups so that they can be identified later.
3.
Plug the pH probe into DrDAQ and run PicoLog software.
4.
Optionally, you can calibrate the pH probe using buffer
solutions.
5.
It is important to allow all the drinks to stabilise at room
temperature since pH readings vary with temperature.
Diagram showing the experiment set up
Carrying out the experiment
Here is a table showing
the pH of some common substances for reference.
Before starting the
experiment, make a table listing drinks that you will test and indicate what
you expect the pH of each drink to be.
Gently agitate the pH
probe in each liquid for a minute or two while the pH reading settles then
record the reading in the table and move onto the next liquid. NOTE Take care
to thoroughly clean the pH probe in a large container of water between each
liquid to reduce cross contamination of the liquids.
When you have
tested all your available drinks, plot the results on a bar graph with each bar
showing the expected value and recorded value for each liquid.
Result
|
Drinks
|
pH
|
|
Apple juice
|
3.49
|
|
Orange juice
|
3.84
|
|
Black tea
|
6.37
|
|
Black coffee
|
5.51
|
Questions and discussion
of results
Q1. With respect to the results you have obtained, can you make any
predictions about the likely pH values of the foods and drinks we consume ?
In chemistry, pH is a measure of
the activity of the hydrogen ion. Pure water has a pH very close to 7 at 25°C. Solutions
with a pH less than 7 are said to be acidic and solutions with a pH greater
than 7 are basic or alkaline. With respect to the results we have obtained, we
can predict that the pH of the majority tested drinks are acidic and neutral.
Q2. Find the pH of a solution whose 
is 9.5E-8M
is 9.5E-8M
Based from the question number 2, when the concentration of
hydrogen ion, [H+] is 9.5x10-8 M, the pH value is,
pH = - log [H+]
= - log (9.5 x 10-8 M)
= 7.02
Q3. Calculate the of a solution with a pH of 5.45
of a solution with a pH of 5.45
From question number 3, a solution with a pH of 5.45 has the
concentration of hydrogen of 3.5 x 10-6
M. The calculation is as follow:
pH
= - log [H+]
[H+] = anti -log (-5.45)
= 3.5 x 10-6 M
Q4. How does the pH reading of a
liquid vary with temperature? (possibly heat a buffer solution)
Let's begin with
the words acidic and basic as extremes which describe solutions as hot and cold
are extremes which describe temperature. Just as mixing hot and cold water
evens out the temperature, mixing acids and bases can cancel their extreme
effects and is then considered neutral. pH is a scale that is used to measure a
substance's acidity. pH scale can tell if a liquid is more acid or more base,
just as the Fahrenheit or Celsius scale is used to measure temperature. The
range of the pH scale is from 0 to 14 from very acidic to very basic. A pH of 7
is neutral. A pH less than 7 is acidic and greater than 7 is basic. Each whole
pH value below 7 is ten times more acidic than the next higher value. For
example, a pH of 4 is ten times more acidic than a pH of 5 and a hundred times
(10 X 10) more acidic than a pH of 6. This holds true for pH values above 7,
each of which is ten times more basic (also called alkaline) than the next
lower whole value. An example would be, a pH of 10 is ten times more alkaline
than a pH of 9.
While an absolutely
accurate measurement of pH levels requires advanced equipment, a rough
measurement can be made with pH test strips. An acid-base indicator is a weak
acid or a weak base. A staple of chemistry labs all around the world, these
inexpensive strips are simply dipped into the liquid whose pH level is being
gauged. After a short while, the color of the strip will change, and the final
color is then compared to the rainbowlike color palette on the package, where
each shade is assigned a pH number. Darker colors usually mean a high pH value,
while lighter colors indicate low pH levels. Indicators have a very useful
property - they change color depending on the pH of the solution they are in.
This color change is not at a fixed pH, but rather, it occurs gradually over a
range of pH values. This range is termed the color change interval. Each pH
indicator is defined by a useful pH range.
For example
Phenolphthalein changes from colorless at 8.0 to pink at 10.0. And Bromthymol
Blue has a useful range from 6.0 (yellow) to 7.6 (blue).
Temperature will have a
measurable yet very slight effect on the pH of water. In fact, pure water has a
pH of exactly 7 only at 25 degrees Celsius, or 77 degrees Fahrenheit. As the
water temperature goes up, pH goes down. The converse is also true, in that
colder water has a higher pH value. At 60 degrees Celsius (140 degrees
Fahrenheit), pure water will register a pH value of 6.96. In other words, the
change is very slight and cannot be registered with crude measurement
techniques such as pH test strips. The reason temperature affects water's pH is
that water molecules tend to break down into their constituents, hydrogen and
oxygen, as the temperature increases. As temperatures increase, a larger
proportion of water molecules break up, producing more hydrogen, which then
increase the pH of the water.
ENHANCE PHASE
According to the problem statements in engaging phase, the
students tasted his oranges juice to be sourer than it should be. He was doubt
on how the concentrations of the juice affect the taste and why the tastes of
various drinks are different. He also thinks why pH leads to diseases such as
cancer. Basically, the tastes are due to the pH value. Technically, the pH of a
solution depends on measuring concentration. The pH value in acidic range for
the high concentration of solution is lower than the pH value for the solution
that is high in concentration. High concentration solution has high concentration
of H+. The concentration of H+ leads the value of pH. For
example, the concentrations of 0.02 M of solution have low pH than the 0.05 M
solution. The concentration of the juice is maybe higher than usual. The taste
for the acidic is sour. Besides that,
various drinks have different tastes because pH values of the drinks are
different. Some of the drinks are sour because it is acidic and the others are
bitter because it is basic or alkaline. There are also neutral drinks with pH
7.
Consumption
of many acidic foods can lead to severe diseases such as cancer because acidic
conditions inhibit nerve action in our human body. That is why we should
balance our diet as it helps to maintain the pH balance of the blood. When we
consume more acidic food, our blood will develop a more acidic condition. Then
the body will inevitably deposit the excess acid to another area of the body so
that the blood will be able to maintain an alkaline condition. As this cycle
continues, these areas will increase in acidity and some cells will die. The
dead cells will then turn into acids. Some cells may adapt and instead of dying
as normal cells do in an acid environment, they will survive by becoming
abnormal. These abnormal cells are known as malignant cells. Malignant cells do
not correspond with brain function or with our DNA memory code. Malignant cells
grow indefinitely and without order. This malignant cell is known as cancer.
