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.

L3. Osmosis

On Monday 6th of October we started a a new experiment called "Osmosis", the main objectives were to know about the osmosis phenomena and understand the process of osmosis in plasmatic membranes. This experiment was divided in two other experiments (with the potato and with the egg).

MATERIALS:

-Egg
-Potato
-Salt
-Distilled water
-Acetic acid
-Spatula
-250 ml beaker
-3 clock glass
-Pen
-Spoon
-Knife

PROCEDURE

Potato experiment:
1- First we sliced the potato in three parts lengthwise, the slices had to be 1,5 cm thick more or less.
2- Then we took the spoon and made a hole in the center of the potato (the hole didn't cross the slice) and then we put the potato pieces in three clock glasses.
3- In the first slice we didn't put anything, in the second we put salt and lastly we filled the hole of the third potato with distilled water.
4- We left this preparation for the rest of the class to see what happens.

Results, observations and conclusions: Our hypothesis was that in the second case the potato would expel water because the concentration of salt of the potato is lower, and in the third case the potato would absorve the water because the concentration of salt is higher in the cells of the potato (distilled water doesn't have any salts). The first potato was to control and compare the results. We were correct!! At the end of the class we saw that the second slice was full of water and the third one was dry, also the teacher told us that the second potato will become softer, plasmolysed, because it has less water and the third potato will become harder, turgid.
We saw the osmosis phenomena because the water went from a hypotonic environment to a hypertonic through a semipermeable membrane to equalize the solute concentration on the two sides. So the potato absorved or expelled water because of this phenomena.

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Egg experiment:
1- First we put the egg in a 250 ml beaker with acetic acid and left it a couple of days.
2- When the outer shell was disolved and only the membrane was left we weighed the egg.
3- Then we cleaned the beaker and put the egg in distilled water.
4- We waited some more days and then we poured out the distilled water and weighed the egg again.
5- Next we put the egg in water with 3 spoons of salt.
6- After a couple of days we weighed the egg again.

Results, observations and conclusions: We remembered our last experiment to remove the shell ( "CH3 COOH + Ca CO3 --> CO2 + (Ca (CH3COO)2)" ), then our hypothesis was that the egg would do the same thing as the potato, and it's partially true. The membrane under the hard outer shell of the egg is semipermeable and it allows air and moisture to pass through. Because water molecules can move into and out of the egg but larger molecules cannot, the semipermeable egg membrane allows the osmosis. So when the egg was submerged into distilled water, the cells of the egg had a higher concentration of salts so the water went to the hypertonic environment and the egg absorbed this water and became turgid. We can confirm this because we weighed the egg and the weight was bigger: at the beginning the egg's weight was 156,3 grams and after was 178,8 (the egg gained  22,5 grams of water). Then the egg was submerged into water with salt and we thought that the egg would expell the water so it would loose weight but the opposite happened, the egg absorbed even more water!! We weighed it and it's weight was 186,7 grams (it gained 7,9 grams) This happened because we only put 3 spoons of salt in the water, so the concentration of salts inside the egg was still higher than in the water. We should of put more salt if we wanted the egg to plasmolyse. Again, we saw the osmosis phenomena in both cases.

QUESTIONS

Egg experiment:
1- What is happening when the shells are soaking of acetic acid? Bubbles start to appear (CO2) cos the calcium carbonate starts disolving.

2- Write the results of the dimensions and weigh of the egg before and after immersing it in distilled water. Write and draw a simple diagram of the water direction.
Beginning: 156,3 g
After distilled water: 178,8 g
After water with salt: 186,7 g

Potato experiment:
3-Explain the results of this experiment. 
I already did earlier.

4- Why have we left the first slice without any treatment (salt or distilled water) ? Because it was the control one, it didn't change, we use it to compare  the other results.

5- Which are the dependent and independent variables?
Dependent: the turgidity of the potato
Independent: the treatment, salt or distilled water.

General questions:
6- How can you explain (through osmosis) the ability of plant roots to draw water from the soil?
In the cells of the plant there are salts so when you put water, there is more concentration of salt in the plant and the water goes to the roots (from hypotonic to hypertonic).

7- What will happen if a saltwater fish is placeed in a freshwater (low concentration of salts) aquarium?
It will die because the concentration of salt in it's body will be higher so the water from the aquarium would be absorbed by the fish.

8- Look the image you have below and explain what is happening to the erythrocytes in each situation:

In the first case the water is expelled from the cells because the concentration of salt out of the cells is higher than in them so they loose water and they get plasmalysed. In the second case water is absorbed and expelled so it's isotonic the concentration of salts is already equalized. In the third case water is absorbed so the cells become more turgid, the concentration of salts is higher inside the cells.

L2. Mineral salts in organisms

On Monday 29th of September we started an experiment called "Mineral salts in organisms", the main objectives were to identify mineral salts in organisms and to understand the function of inorganic biomolecules in skeletal structures of organisms.

First we gathered all the materials that we needed: 
-Molluscs's shells
-Dried cleaned chicken bones
-Distilled water
-Acetic acid
-Vinegar
-250 ml Beaker
-Clock glass

PROCEDURE

Chicken bones:
1- We took the chicken bone and made sure that there was no meat remaining on it, also we cleaned it with water.
2- After that we weighed the bone, the weight was 13,5 g.
3- Then we tried to bend the bone to check it's flexibility, it was not flexible at all.
4- We took the beaker and put vinegar in there, with a small amount of acetic acid.
5- Then we dropped the bone in the solution that we made and covered the beaker with the clock glass to protect it.
6- All that we had to do is wait 24-48 hours to see what happens to the bones but we decided to wait a week because the bone is really thick.

Results and observations: We left the bones in the solution for a week and when we tried to bend them again with the tongs, they did.

Conclusions: The bones are now flexible! They lost their stiffness because they don't have calcium carbonate anymore, and only the organic material is left.

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Mollusks shells:
1-We took another beaker and put acid acetic and distilled water in there.
2-Then we put the shells in the beaker.

Results and observations: When we put the shells in the beaker a lot of bubbles started forming and soon the entire beaker was covered with bubbles (it was very fizzy) , it looked like an effervescent pill. Then we decidded to leave the solution for a few days to see what happens, on the third day there was no signs of the small shell in the beaker and the big shell was disolving. Ignacio decided to try this experiment with and egg shell and the same happened to it, but there were brown rests of egg shell and the membrane.

Conclusions: What happened is that the shells contain Ca CO3 (calcium carbonate), when it combines with acetic acid a chemical reaction takes place and CO2 (carbon dioxide) is released (those are the bubbles) and (Ca (CH3COO)2) calcium acetate is formed. So the inorganic materials dissolve and all that there's left are the organic materials.

 QUESTIONS

1- Write the reaction that takes place when the acid acectic reacts with the calcium carbonate.
CH3 COOH + Ca CO3 --> CO2 + (Ca (CH3COO)2)
When calcium carbonate reacts with acetic acid it produces carbon dioxide and calcium acetate.

2-What is happening when the shells are soaking of acetic acid? What are the bubbles that you can see? When the shells are soaking of acetic acid they make a lot of bubbles and the soulution is fizzy. The bubbles are CO2.

3- What is happening to the bone after some days of soaking it in acetic acid? Why is the bone flexible now?
The bone become more flexible, we can now bend it with the tongs. The acetic acid dissolves the calcium carbonate of the bone and only the organic material is left, so the bone looses it's stiffness.

4-So, what is the function of the calcium carbonate in the skeletal structures? To give rigidity.

5- Increases in carbon dioxide to the atmosphere from the burning fossil fuels and deforestation threaten to change the chemistry of the seas. Evidence suggests that this increase in atmospheric carbon dioxide is lowering the pH of the oceans in a process called ocean acidification. How can acidification affect coral reefs?
The coral reefs are made of calcium carbonate (CaCo3), if the acidity is higher they will disolve. The lowering of the pH will disolve the CaCo3.