L4. pH

On Monday 13th of October we started another experiment called "pH" the main objectives were to measure different pH values of organic and inorganic solutions and to prove different methods of measuring pH. The pH is the measure of the acidity or basicity of a solution. Solutions with pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. Pure water has a pH close to 7, it's neutral. The pH is defined as the following equation:

pH = -log (H+)

MATERIALS:
-Distilled water
-Milk
-Wine
-Tomato
-Coffee
-10% NaOH solution
-10% HCl solution
-NH3 solution
-Soap Solution
-Bleach
-Universal indicator paper strips
-pH-meter
-Acetic acid
-Tongs
-Lemon
-Beakers
-Clock glass
-5 test tubes
-Test tube track
-10 mL pipet
-Funnel
-Graduated cylinder

PROCEDURE:

Universal indicator paper strips experiment:
With this experiment we wanted to measure the pH of different solutions, so we put different solutions in small beakers of 250 mL. We used: milk, wine, tomato, coffee, soap soluton, NH3, NaOH and HCl. For example: we squeezed the tomato in a clock glass and then we put the piece of paper  into the solution. Then we removed the indicator paper and compared its colour with the colour chart.

Results, observations and conclusions: This picture shows the results of each solution, it shows its pH.

"How does concentration affect pH?" experiment:
First we squeezed the lemon juice inside a graduated cylinder using a filter made of celluose paper and a funnel, then we prepared a test tub rack with 5 test tubes cleaned with distilled water; we marked the tubes with the label: A, A1, A2, A3 and B. The next step was to add 10 ml of lemon juice to tubes A and B, then we took the A tube and put 5 mL of its lemon juice to test tube A1. Then 2,5 ml of the test tube A1 to tube A2. Lastly, we took the A2 tube and put 1,2 mL of it lemon juice to tube A3. The final step was to add distilled water to each test tube until it had the same volume as test tube B (10mL). Then we measured each pH with the strips and with a pH-meter.

Results, observations and conclusions: 
We calculated the concentration by doing this equation:

Concentration (%) = (Volume of Juice / Total Volume) · 100

Our hypothesis is that if we have a high lemon juice concentration we expect it to be the most acid because it has the most concentration of protons. But in the chart we see that in our case this is not happening; the test tubes with a higher concentration of lemon juice in them, have a lower pH, they are the most acid!
Maybe the problem was that the pH-meter wasn't calibrated correctly.
Our classmates Ignacio and Eduard got it right because they were the first ones to use the pH-meter, and we can accept our hypothesis. You can see how they did it HERE.

Graphic:

QUESTIONS:

1-Which of the solutions fave an acid pH? HCl, vinegar, wine, tomato, coffee and milk.

2-Which of the solutions were alkaline? Soap, bleach and NaOH.

3- Which of the solutions were neutral? Did you expect this results? Explain 
Distilled water was neutral, and yes we expected this results because it has no mineral salts and it has the same number of H+ and OH- ions.

4- How does a pH of 3 differ from pH 4 in terms of H+ concentrations? A pH of 3 means that it has 10^-3 H+ and is more acid and a pH of 4 has 10^-4 H+ .

5-In the second part of the experiment, you have compared the pH of the same product (lemon juice) in different concentrations. In this case explain:
a) Which is the dependent variable? pH
b) Which is the independent variable? The concentration
c) Which if the problem that we want to solve? We want to see if the pH depends of the concentration.

6-Which pH do you think that gastric juices might have? Why? Do you think that intestinal pH has the same pH why?
They will have 2 because gastric juices have HCl.  In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes. The liver secretes bile into the duodenum to neutralize the acidic conditions from the stomach, and the pancreatic duct empties into the duodenum, adding bicarbonate to neutralize the acidic chyme, thus creating a neutral environment. The mucosal tissue of the small intestines is alkaline with a pH of about 8.5

7-Which pH do you think that blood might have? Why? Neutral because the intern fluids have to have a neutral pH because if it wasn't like that we would die.

8-What is acid rain? which are the consequences in the ecosystems and how is its formation pattern? Is rain in Barcelona acid or alkaline?
Acid rain is rainfall made so acidic by atmospheric pollution that it causes environmental harm, chiefly to forests and lakes. The main cause is the industrial burning of coal and other fossil fuels, the waste gases from which contain sulphur and nitrogen oxides which combine with atmospheric water to form acids. In Barcelona the rain is alkaline, maybe just slightly acid.