Overall Conclusion

By analysing the results achieved from the three experiments, a clear and coherent conclusion may be drawn.

In the Chemistry section, where the pH was tested, the average pH for the Lagoa Rodrigo de Freitas was of 8.75 and for Ipanema beach, the value was of 7.25. As the Ipanema beach's value is much closer to the expected value of a clean water, with few impurities and the value for the Lagoa may be considered significantly high, the results led to believe that the Lagoa's water was obviously more polluted.

In the Physics section, where density and refractive indexes were tested, the sample containing water from the Lagoa turned out to be denser and thus have a larger refractive index, whereas the sample with water from Ipanema was less dense, more similar to pure water, given the fact that seawater and not fresh water was being dealt with. Since a higher density means more impurities, the conclusion drawn from this experiment was also that the Lagoa's water was more polluted.

Last but certainly not least, the Biology section provided the group with the final, visual and more concrete proof to reach a final conclusion. From the final samples, the petri dish containing water from the Lagoa presented a much larger bacterial growth than the one with water from the Ipanema beach and with this, the same conclusion as the other experiments was reached: the Lagoa's water was more polluted.

Therefore, one can safely affirm that, through these three comparisons, the Lagoa's water is certainly of a lower quality and thus has a higher level of pollution. However, it is certainly not correct to affirm that the water from Ipanema is clean. It is simply cleaner than the Lagoa, but also suffers from the same problem and much has to be made to finally solve it.

Chemistry - Testing Water pH

What is pH and the pH scale? – A more complex approach.

In Chemistry, pH is the measure of the acidity or alkalinity of an aqueous solution. Pure water is said to be neutral, with its pH being approximately 7.0 at r.t.p. The pH scale ranges from 0.0 to 14.0. Aqueous solutions with a pH value from 7.0-14.0 are said to be alkaline or basic and solutions with pH from 0.0-7.0 are said to be acidic. pH measurements are important in many fields, including medicine, biology, chemistry, agriculture, forestry, food science, oceanography, civil engineering and many others.

The idea of pH is actually a mathematical concept as the pH scale is a logarithmic one. This means that each change of pH 1 in the scale corresponds to 10 times more or less acidity/alkalinity. For example, pH 4 is ten times more acidic than pH 5 and 100 times more acidic than pH 6. The same holds true for pH values above 7, as pH 11 is 10 times more alkaline than pH 10 and 100 times more alkaline than pH 9, for example.
As the pH measures the acidity/alkalinity in an aqueous solution, the idea behind this concept lies on the ionization of water. Water molecules exist in equilibrium with hydrogen and hydroxide ions as some of the molecules tend to dissociate into ions. The water equilibrium constant is written as:

Kw = [H+][OH-]

Experimentally, it has been found that [H+] = [OH-] = 10-7.
Therefore K=[10-7][ 10-7] = [10-14]

Now, as an acid is known to donate H+ ions (proton donor) and an alkali is known to accept H+ ions (proton acceptor), if an acid (which contains the H+ ion) is added to water, the equilibrium shifts to the left and the OH- ion concentration decreases. The opposite happens when a base (containing OH- ions) is added to the solution, where the concentration of H+ ions decreases. This follows the Water Equilibrium Principle: the product of H+ and OH- ion concentration must always be equal to 10-14.

The concentrations of hydrogen ions and, therefore, indirectly, of hydroxide ions are given by a pH number. 
pH is defined as the negative logarithm of the hydrogen ion concentration. The equation is:
pH = -log [H+]
Thus, this means that H+ ion concentration and pH are inversely proportional whereas OH- ion concentration and pH are directly proportional.

pH in seawater
Due to its salinity (approx. 3.5% of the average seawater’s mass), seawater tends to be a little alkaline, being limited to the range of 7.0/7.5-8.4. However, impure seawater tend to leave this range and, as this is a global one, in specific locations, smaller ranges can be established which therefore means that smaller  variations may determine if the water is pure or impure.

Where our Project comes in
In our project, the group is going to measure the pH of two samples of water: one from the Lagoa Rodrigo de Freitas and one from the Ipanema beach. As it was previously mentioned, the Lagoa Rodrigo de Freitas is a lagoon connected to the Ipanema beach. Therefore, it contains salt water but its salinity is reduced compared to that of Ipanema beach as it receives fresh water from rainwater and rivers which flow into the lagoon, such as the Rio dos Macacos. By knowing the pH value of a sample for each location, we will be able to know the level of purity of each site ad consequently, the level of pollution.


There are many ways to measure the pH of a substance. Some of them are by using pH indicator paper, Universal indicator solution, a probe and meter and litmus paper. Save for the probe and meter, which was not available to the group at the school, the other forms of measurement can turn out to be subjective to a certain extent. Therefore, the group reached a consensus of using two methods: the universal indicator solution and the pH indicator paper.

1.       After having followed all of the safety precautions necessary, place one pH indicator strip on a petri dish and, using a pipette, add a few drops of one of the samples of water (Lagoa or Ipanema) until the strip is covered in water. Wait a few seconds and record the reading according to the table on the pH indicator paper package.

Comparing colours obtained with those in the scale. (Ipanema - right, Lagoa, left)
2.       Repeat the same process with the other sample of water (Lagoa or Ipanema).

Gabriel comparing the results from each sample with the pH scale from the Indicator paper package.
3.       Place 50 cm3 of one of the samples (Lagoa or Ipanema) inside a large test tube. Using a pipette, add a few (3-4) drops of Universal Indicator solution to the sample and mix it. With a copy of a precise pH table beside, compare the colour seen with the one in the pH table and record the pH.

The difference in colour (and therefore pH) between the two samples (Ipanema - right, Lagoa -left).

4.       Repeat the same process with the other sample of water (Lagoa or Ipanema).


pH Indicator Paper/ pH
Universal Indicator Solution/ pH
Ipanema Beach
Lagoa Rodrigo de Freitas

These results may be seen more clearly in the graph below.


As it was mentioned previously, the pH of seawater varies within the range of 7.0/7.5-8.4. It therefore may be seen that the water in Ipanema, through this experiment which analyses only the variable of pH, may be considered clean as it is near the neutral zone, which indicates that it has no additional impurities which may change its pH. The Lagoa's water, however, surpasses the acceptable range and can be considered significantly alkaline, especially due to the fact that its level of salinity is smaller than that of Ipanema and therefore, the change in pH is caused mainly by impurities due to pollution instead of dissolved minerals. A plausible reason for the high pH may be the high amount of heavy metals which studies have proven to have found in the Lagoa's water, as mentioned in the introduction to the project. These heavy metals can react with the water, forming metal hydroxide, which are basic substances which thus increases the water's pH.

Sources of Reference:


Biology - Testing for Bacteria in Water

What are bacteria?

Bacteria are single-celled prokaryote micro-organisms. Prokaryotic cells are cells that have no nucleus in them. The diagram below shows a prokaryotic cell:

Bacteria can live in any habitat on Earth. They can grow in soil, acidic environments, hot springs, radioactive waste, water and deep in the Earth's crust as well as in organic matter and living bodies of plants and animals. In industry, bacteria are important in sewage treatment, the production of cheese and yogurt through fermentation, as well as biotechnology and the manufacture of antibiotics and other chemicals.

But how can bacteria be harmful to us?

There are approximately ten times as many bacterial cells in the human flora as there are human cells in the body, with a high number of bacteria on our skin. The vast majority of bacteria in our body are harmless due to the protective effects of the immune system and a few are even beneficial. However, there are a few species of this micro-organism that cause infectious diseases including cholera, syphilis, leprosy and bubonic plague. The most common fatal bacterial diseases are respiratory infections such as pneumonia, which kills about 2 million people per year. Even though bacterial infections are extremely dangerous, they are treatable by antibiotics.

Bacteria in seawater

Since the Ipanema beach and the Lagoa suffer pollution especially from sewage disposal, the water may contain some types of bacteria, with the most common one being E. Coli. As mentioned in the introduction to the project, studies have shown that prolonged contact with the waters from Ipanema beach and Lagoa can indeed cause various diseases including cholera, typhoid, dysentery, hepatitis and others.

Where Our Project Comes In

In this project, the group will test for bacteria in the two samples of water from both locations being investigated. By investigating the amount of bacteria in the water, the students can have an idea of the water's level of pollution. The chance of finding bacterial life in the samples of water is very big, but what will determine the difference between a clean and a polluted sample is the amount of bacteria found.


1.  After having followed all safety precautions necessary, place 10 cm³ of each sample of water inside a separate, small test tube and place the test tubes inside a centrifuge. Each water type has two samples: one at room temperature and one which has to be previously boiled using a bunsen burner or a kettle.

2.  Centrifuge the samples for 10 minutes.

3.  Get one sample and, with a pipette, carefully add a few drops of the sample of water on top of the agar jelly on a petri dish and seal the petri dish.

4.  Repeat the same process with the other 3 samples of water.

5.  Leave the petri dishes inside an incubator at 37 oC for 48 hours.



As it can be clearly seen in the diagrams in the results section, as expected, the boiled samples presented a smaller bacterial growth than the ones kept at normal temperature. But comparing the samples from each site, it can be clearly seen that the sample with the water from the Lagoa Rodrigo de Freitas presented a much larger bacterial growth than the one from Ipanema, which leads us to believe that there is a higher bacterial concentration in the water from Lagoa than the one from Ipanema, and thus, from this variable, it is more polluted.

Physics - Testing Water Density through Refraction

What is Refraction?

Refraction can be described as the bending of waves as they move from one medium to another one, with a different density. As light travels through a given medium, it does so in a straight line. However, when light passes from one medium into a second medium, the light path bends and the process of refraction occurs. The refraction occurs only at the boundary. Once the light has crossed the boundary between the two media, it continues to travel in a straight line. Only now, the direction of that line is different than it was in the former medium. Light rays are refracted when they go from air to water since water has a higher density than air. 
The image above shows the waves bending as they change media. Since the waves in the second medium are closer to one another and have gone closer to the normal, one can assume that this is the medium with a higher density. The same will happen when light goes from air to water. 

The amount by which light bends when it enders a medium is known as its refractive index. The refractive index of air, for example, is approximately 1.00 while that of pure water is about 1.33. This means that when light goes into water from air, it will bend towards the normal. It is a fact that the refractive index usually increases with the density of the medium. Have you ever thought of why we need goggles to see under water? The answer to that is simply because water has the same refractive index as the vitreous humour in your eyes, and thus, refraction does not happen to focus the image on the back of your retina and the image cannot be formed.

How Our Eyes Work:

The process of vision begins when light rays that reflect off objects and travel through the eye's optical system are refracted and focused onto a point of sharp focus.

Just as a camera's aperture (called the diaphragm) is used to adjust the amount of light needed to expose film in just the right way, the eye's pupil widens or constricts to control the amount of light that reaches the retina.

In dark conditions, the pupil widens. In bright conditions, the pupil constricts.So that we can see, light enters our eyes and is refracted to focus on the back of the retina. In the retina, there is a high density of photosensitive cells which will respond to the exposition to light. In order to focus the light, a lot of refraction needs to happen in the lens as well as the vitreous humour. If water has the same refractive index as one's eyes, that refraction would not happen. 

Density and Pollution

As previously mentioned, the higher the density of an object, the more refraction occurs and therefore, the larger the refractive index. In pure water, which has no impurities, the refractive index is approx. 1.33. However, if impurities were found in the water, obviously, the density of the medium would increase and therefore, increase its refractive index. Thus, polluted, impure water, due to its increased density, will refract light more than pure water.

Where Our Project Comes in

Since the aim of our project is to test for water pollution and compare two samples of water, a way of doing so is by applying what was said in the previous paragraph. Our group will therefore test for refraction in the two samples of water, from Ipanema beach and the Lagoa Rodrigo de Freitas and thus, the one with the higher level of refraction is the denser and therefore, most polluted one.

As the topic of refraction is indeed interesting, the previously mentioned section of the eye and how one cannot see under water was only put as an additional research to our investigation, as the members of the group indeed found this topic really interesting and decided to add to the project by including it.


In order to test for the refreactive index, there is a variety of methods to be used. The first one is to half fill a beaker with water. We would use two beakers, one for pure water and another for sea water. then place a straw with a diagonal orientation in the water so that some of it is not submerged. refraction should be clear but now, we would have to compare the distortion of the straw in both cases. Since we are testing for impurities, we have also to use the process of centrifuging in the samples to be tested. this would remove at least some of the salt in the waters. These would make the test unfair since the sea water would obviously have a larger salt content.
  1. Add the same amount of centrifuged water to three different beakers, remembering to lable them.
  2. Put a straight object into the water to show refraction. A good idea is to use a straw with the red marks on it since this would create a more specific point of comparison between the three samples
  3. Repeat the same process for the other sample of water.
  4. The results will be given through the amount of refraction that happens in each sample, that is, the amount that the red line is distorted.
Refraction is obvious but enhanced by the red orientation


Below are the results obtained, the pictures can be compared in order to concude that the water from teh Lagoon has a larger refractive index than that of the one in Ipanema well as that of distilled water. If you are still unsure, we can prove this even further!! The refactive index is also directly related to the density of the susbtance, the more dense it is, the higher is the refractive index. To discover density, we use the formula density=mass/ volume. The same volume was tested in each case (75cm³) and we found that from these three, the water from the Lagoa Rodrigo de Freitas has the higher density.

Pure Water
Mass (g)
Volume tested (cm³)
Density (g/ cm³)


 From the results obtained from testing the density of water, we could conlude that the water has a higher density in the Lagoon. It is interesting to observe that this was a common conclusion in the other experiments. This means that in terms of refraction in our eyes, it would be harder to focus in the water of the Lagoon since it has a higher density than teh vitreous humour in our eyes. That means that even though more refraction would happen in comaprison to in pure water, light would me moving into a less dense subtance causing it to refract wrongly. Rather than focusing, thsi would couse light to spread further.


Centrifuge the samples of water collected in order to remove the excessive salts but maintain the impurities.

Safety Precautions

Before the group started the experiment, safety was a very important issue to worry about, as, in a science laboratory, the students worked with glass, chemicals and other dangerous equipment and substances, and thus precautions always have to be taken.


The first precaution taken followed was to use proper shoes and not sandals, flip-flops, etc. This is important since a substance or a piece of equipment might fall on the floor and, by wearing shoes, the students' feet were protected .


Another important precaution was to wear safety goggles for eye-protection. When doing an experiment, observation of the processes are always necessary and, if an unexpected happening occurred, such as a violent reaction or a piece of equipment breaking, 


When the results on some measuring equipment such as a measuring cylinder or a thermometer had to be read, it was done similarly to the picture above, at eye level, to avoid parallax. However, it is necessary to maintain a certain distance from the equipment, especially if it is a dangerous/ harmful substance being measured or if the equipment being dealt with is fragile.


When working with boiling tubes,the students made sure always to point it away from people and themselves, thus preventing them from hurting themselves is a sudden, unexpected reaction occurred. (Note: This picture was takes before the group decided to change part of its experiment. The previous changes section of the experiment dealt with investigating boiling points, which explains the equipment being used above.

Introduction to Our Project - Investigating Water Pollution

Every “carioca” knows that the quality of the water in the Lagoa Rodrigo De Freitas, the city’s most famous lagoon, isn’t the best one, and is indeed appalling although studies have shown that the level of pollution has significantly decreased in the past few years. In the Ipanema beach, one of the most famous beaches in the world, which is in fact connected to the Lagoa Rodrigo de Freitas through the Jardim de Alah, as seen in the map, the quality of the water is obviously better. But a growing concern amongst the population of Rio de Janeiro is the increasing level of pollution that the beach overcame in the past few years due to innumerous reasons which will be presented later.
Therefore, in this project, the group consisting of 5 IB Experimental Science students aims to investigate the level of water pollution in these two famous spots of Rio’s beaches and salt water lagoons using different methods for each of the three branches of science: Physics, Chemistry and Biology. The group consists of two IB Chemistry students, Gabriel Fritsch and Lucas Biolchini, two IB Biology students, Jonas Adler and Ana Carolina Augusto and one IB Physics student, Olga Saadi, who will work together, each contributing in their own fields towards the project’s completion.
The way which the group chose to integrate the three sciences in testing the level of pollution of different samples of water was simple but led to much reflection. For the Chemistry part, it was decided that the acidity of the samples of water would be tested. The farther from pH 7, the higher the water’s level of pollution. To integrate Biology into the investigation, the water would be tested for bacteria and microorganisms and, last but not least, for the Physics part, the group decided to investigate the effect that impurities and different levels of salinity have on the process of refraction of light in water.
An in-depth explanation of each of the separate investigations, with methods of data collection and results will later be posted here in our blog. Now, let us know more about the two locations we are investigating.

Ipanema Beach
The city of Rio de Janeiro is the largest coastal city in Latin America and one of the largest in the world. It is globally known for its peculiar landscape, with huge mountainous structures being immersed directly into the city’s famous beaches, bays and lagoons. Ipanema beach is a famous example. However, the consequences of the pressure on the ecosystem due to the demographically dense metropolis are evident in the increased level of pollution that the water presents. This has specifically risen in the past 2 decades.

Visibly polluted water being carried between Ipanema Beach and the Lagoa. 

The main reasons for this are the “canais da maré”, the tide channels, which make the connection between lagoons and urban draining adjacent to the sea with the beach and the famous “línguas negras”, the “black tongues”, the underground plumbing system which carries rainwater and urban draining near the beach to the sea. Another significant source of pollution are the submarine emissaries which carries the urban sewage to areas farther from the coast, but which, given certain meteorological and oceanographic conditions, these polluted remains reach the Ipanema beach, thus further jeopardizing its water quality.
According to the CETESB (the Rio de Janeiro’s state Company of Environmental Sanitation Technology), the prolonged contact with the beach’s water, where the possibility of ingesting significant amounts of seawater is high, may indeed cause various types of diseases, including gastroenteritis, infections in the eyes, throat, nasal cavity and ears, dysentery, typhoid, cholera and many others. Studies have shown that in during the months where the rainfall is most concentrated, the water from Ipanema beach show high amounts of total coliforms and E.Coli.

Lagoa Rodrigo de Freitas
The Lagoa Rodrigo de Freitas is a common example of a salt water lagoon formed by the depoisition of sand due to a sudden change in the coast’s shape, which forms a bar beach, impeding its contact with the sea. However, the Lagoa as it is popularly known, is connected to the Atlantic, allowing sea water to enter, by a canal known as Jardim de Alah.
The Lagoa and its visibly dark, polluted  water.
For many years, the Lagoa has suffered with the harsh consequences of pollution. One of the main sources of this problem is the several illegal sewage disposal systems connected to the lagoon, which release several toxic substances into the lagoon’s water (studies have found high concentrations of heavy metals such as copper, nickel and zinc in the lagoons water, with values higher than the acceptable limits) and also generate a large nutrient stock which causes another problem: eutrophication. Due to the high level of nutrients, a rapid increase in microalgae production occurs resulting in a loss of the water’s transparency and increased oxygen consumption thus creating an oxygen deficit in the Lagoa’s water. The lack of oxygen significantly reduces wildlife as it kills many of the species which cannot carry out the necessary processes to survive with such a low level of oxygen. As these microalgae and other species decompose, an excessive amount of bacteria may be spotted.
Dead aquatic life due to toxic substances and eutrophication in the Lagoa. 
Similarly to Ipanema beach, the bacteria present in the Lagoa Rodrigo de Freitas’ water can cause all of the diseases aforementioned. A plan, made through a partnership between EBX, Eike Batista’s (the multi-millionaire Brazilian entrepreneur) company and the Rio de Janeiro City Government called Lagoa Limpa is being currently put into action which aims in depolluting the Lagoa and has already produced positive feedback that the quality of the water is indeed improving.

Sources of Reference:

Introduction to the Group 4 Project

The Group 4 Project is a project which every IB Experimental Science student has to undergo as part of the internally assessed coursework which composes part of the Experimental Science final grade. The project's idea is for the student to work with others, studying other Experimental Science, in an investigation which can integrate the three branches of science: Chemistry, Physics and Biology.