What is the ph of the soap I use?

1. Introduction 
Ellen Richards was the first woman to enter MIT (Massachusetts Institute of Technology) and is considered the forerunner of environmental engineering. Ellen was very concerned about the quality of air in houses, water for human consumption and, in general, about substances that could influence the health of human beings. 
In this practical exercise, we are going to assess whether the soaps we use every day can have an undesirable effect on us or on the environment. 
The skin is the largest organ of our whole organism, and has such important functions as being the first defensive barrier against the entry of micro-organisms. For this reason, we must be careful about the type of products we use every day for our personal hygiene. Similarly, we must remember that all the sewage and different chemicals we use in our homes end up in the sea in one way or another. 
You will have seen many advertisements on television proclaiming the virtues of different types of skin and hair gels and soaps. Some refer to the pH of these and generally tell us that they are all neutral, so our skin is safe if we use them every day.

2. Objectives and titration 
Many substances behave in aqueous solution as an acid or as a base. In the first case, they release H+, i.e. protons, into the medium, as for example in the following reaction: 
 
Cl H → Cl- + H+ 
 
In the case of bases, when we put them in contact with water, they dissociate, but in this case to generate OH-. For example: 
 
NaOH → Na+ + OH-

The pH values of soaps tell us whether or not the product in question attacks our skin.  
The epidermis is covered by a layer of water and fat that protects the body from bacteria and fungi. This layer is made up of fat, sweat and carbon dioxide from the skin. In addition, it also contains a number of symbiont micro-organisms, the number of which increases when we bathe. All these components determine the pH value of our skin, which is slightly acidic, between 5 and 5.5. Alkaline detergents attack this layer and destroy it. 
After using alkaline soaps for a certain period of time, the skin cannot regenerate. This happens with some bars of soap, which are usually slightly alkaline and dry out the skin very much. 
To avoid this undesirable effect, soap manufacturers often add substances such as lanolin or lecithin, which replace the fat that is lost through the action of the soap. Stone soaps are particularly harmful to hands, as they have a very high pH. By contrast, "neutral" soaps, with a pH value of 7, react neutrally and are more tolerable. Soaps with a slightly acidic reaction are mostly synthetic soaps, but have a similar cleaning effect to the others. 

Finally, don't forget that all the products we use to wash ourselves run down the drains into the sewers. On their way, wastewater ends up in rivers and finally in the oceans. River water usually has a pH between 6.5 and 8.5 and oceans have pH values between 7.4 and 8.4.

 
3. Materials 
  -Test tubes (two for each soap sample) 
  -Gradilla 
  -Pipettes  
  -Filter paper 
  -Filter paper -Filter paper -Embuds 
  -Distilled water 
  pH-indicator solution or pH-measuring strips. 
  -Colour scale 
  -Soap samples  
 
4. Procedure 
1. Label the test tubes appropriately with each of the soap samples. 
2. Introduce a few soap shavings (scraped with a spatula), or two drops of liquid soap, shampoo, etc., into a test tube.  
3. Add 10 cc of distilled water. Close the tube with a stopper and shake until the soap has dissolved (you can leave it uncapped and dilute it by shaking carefully so that the contents do not spill out).
4.  Place a funnel with a filter in another test tube and pour in the soap solution (it will be enough when the filtrate reaches a height of about two centimetres).
5. Add four drops of pH indicator solution. Tilt the tube and measure on the colour scale. Note the value obtained (pH can also be measured by inserting pH indicator strips into the test tubes).
 
5. Questions 
1. Make a table with the soap brands and the pH obtained. 
2. Which is, according to the above, the most suitable soap for skin care? 
3. Does the information given in the advertisements for the product coincide with the results you have obtained? Give reasons for your answer. 
4. What conclusions can you draw about the advertising and the characteristics of the products we consume? 
5. Does the pH of soap solutions coincide with the pH of rivers and seas?  
6. Taking into account the results obtained, investigate: What consequences can the use of soaps have for aquatic ecosystems?