Experiment n5: Recording data from gas pressure

Background information:
It is important that all materials made of glass in this experiment (the schlenk tube) should be dried in an oven before use. The schlenk tube or flask was invented by Wilhelm Schlenk. It comes equipped with a stopcock which allows the vessel to be filled with gases, mainly used for inert gases. Whatever gas that is inserted doesn't matter. The properties are the same for every gas because it is a general law in science.

Aim:
To observe the variability in gas pressure relating it to the temperature.

Variables:
Independent variable (x): The independent variable in this case will be the temperature (tºC).
Dependent variable (y): The dependent variable is the gas pressure, P(hPa).
Constant variable: There are many constant variables throughout the experiment, the most important ones are the gas volume and the gas mass.

Materials:
- Magnetic stirring
- Bunsen Burner
- Tripod
- Container
- Wooden planks
- Clamp
- Stand
- Gas pressure sensor
- Stirrer (magnetic pill)
- Lighter
- Blocks of ice
- Schlenk tube
- Water


Procedure:

1 - Set the whole mechanism up: elevate the magnetic stirring with the wooden planks the height of a bunsen burner and place the tripod underneath. Then, place the container on top, hold the schlenk tube with the clamp and stand and in the container (it is important that the tube cannot touch the base or any of the sides), and place the stirrer in the container as shown in image 1 -->
Also make sure that the gas pressure measurer is connected to both the schlenk tube and the computer to record the data.

2 - Pour enough water so that it covers the schlenk tube entirely. Not a single drop under.

3 - Place 3 blocks of ice and wait for the temperature to drop to its lowest. After this, turn on the bunsen burner to increase the temperature of the water in the container.

4 - For every 3ºC change in temperature, record data on the computer software and observe the change in the pressurised gas. It is important to note that when the 3º has appeared on screen, leave the bunsen burner off for a few seconds until the temperature is stabilised.

5 - Make a graph with the values you have obtained.

Results:
Our group has obtained accurate values and we know this by calculating the value of "R" squared of the graph obtained. Below is a graph showing our results with a line of best fit.

Bibliography:

http://www.youtube.com/watch?v=KW9EITxozzg
http://en.wikipedia.org/wiki/Schlenk_flask

EXPERIMENT n4: Electricity with redox reactions

date of experiment: 05/02/2013

GENERATING ELECTRICITY

Background info:

In redox reactions there's always an element that loses electrons (oxidation) and another who receives them (reduction), and as it is a reaction, energy is released.

Redox couples, like Cu (reducing agent) and Cu+2 (oxidating agent) are clear examples of redox reactions.

When we want to travel, we pay to an airline in order to them to take us in an plane, this means that, if we want to travel, we have to pay. But the pilot in the plane doesn't have to pay (and he maybe doesn't want to travel, but it is his job, so he must do it). With this metaphor we want to explain what is going to happen in the experiment we performed.
But, why does this happens? at first we need to know that current is the flow of electrons, while electricity is the process that involves the whole factors (voltage, current, impedance...), electrons always move from the negative to the positive pole, although we can have differences in the intensity of this flow, in galvanic cells, which are what we are creating in this lab session, the consist of two pairs of redox couples (they are formed by the oxidized and reduced form of an element, for example Cu+2/Cu0), and each of them will act as each of the poles of the battery. what we do in the galvanic cell is separating the two parts of the redox reaction, and connect them by an external circuit, allowing electricity to happen.

Water (H2O) is not a great conductor, but why does it always acts as a great conductor in films? that's easy to explain: water that contains NaCl (table salt), is composed of ionic bonds and its function is of making an ionic equilibrium between the two couples, as there is a difference in the potential of the two parts of it, this difference makes imposible for the electrons to flow anymore, so the function of the salty bridge is not only to close the circuit (a simple wire could do that) but to enable the current to flow.

Aim: 

To create an electric circuit using salt bridges and redox reactions. the redox couples will be conected with wires to a multimeter which will show us the voltage or the current of the circuit.

Materials:

• Multimeter
• Black and red wires (like the ones in the picture)
• Copper
• Copper sulphate (CuSO4)
• Tin
• Tin nitrate  Sn(NO3)2
• 2x beakers
• Cotton
• Salty water
• Water
• Curved cristal tube

Procedure:

1. Take the curved tube and fill 1/4 of it with salty water.
2. Fill it to the end with normal water and put cotton on it's endings so that water doesn't fall.
3. Fill one of the beakers with copper sulphate and another one with the redox couple of tin.
4. Connect one of the endings of the wires to the multimeter and with the other ending hold the copper wire.
5. Repeat step 3 with the tin wire.
6. Dip the copper and tin into their redox couple solution (be careful that the red or black wire don't touch the solution).
7. Turn on the multimeter and look at it's screen (the given value should be of 0, ad we don't have a closed circuit)
8. Place one end of the curved tube in one beaker and the other                                                                        end in the remaining beaker.
9. Now look at the value in the multimeter, it should be around 500

What did just happen?

We've just made a battery. The redox reaction created the perfect conditions for the electrons to flow; we can say redox couples are the passengers in the plane, as they pay electrons for the circuit to work, but why we needed to make a salt bridge (the curved tube) between the two beakers?: It is simple, we had the main components of a circuit, but it wasn't closed, this means that the electrons couldn't complete the circuit and therefore no current was made, but when we placed the salt bridge (which conducted electricity) we closed the circuit and enable the current to flow, we also equilibrated the two parts of the reduction.
We compared our results with the ones obtained by our classmates, and we found out that the current of a group was around 1000 in the multimeter, while our reached 520, how can this be possible?
It all has to do with the reduction potentials of the couples used, for example Cu+2/Cu has a reduction potential of +0.15, when we have a high reduction potential, we could say that the compound desires to be reduced (it is more possible for it to be reduced), while the Tin reduction potential Sn/Sn+2 is of -0.14, this means that it is more possible for it to be oxidized. our classmates worked with different redox couples, and we discovered that the one that got 1000 in the multimeter had a higher reduction potential difference in their couples, this means that the higher the difference in the reduction potential, the more current we are able to create.
The representation for our galvanic cell would be:

Sn/Sn+2//Cu+2/Cu

Bibliography:

• Carnegie Mellon. (2012) Redox Couples. Recovered from http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Redox-Couples-604.html 
• All photos were taken by Juan Senín Vinuesa at the school lab
• Rey.L(2013) Redox reactions. Galvanic cells. Electrolysis. Recovered from https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=d06559dab7&view=att&th=13caea77a2dd1f22&attid=0.1&disp=inline&safe=1&zw&saduie=AG9B_P9mwM03WApaweJF_a6Bn2K6&sadet=1362941816416&sads=o0GFmHN5Aa_93ILfQjGmh0blPqg&sadssc=1 

EXPERIMENT n3: Redox Titration

Aim:

To investigate the amount of hydrogen peroxide in commercial oxygenated water.

Background information:

A titration is a reaction of a solution of unknown concentration with a solution of a known concentration for the purpose of finding out more about the unknown solution. So, redox titrations are very used techniques for knowing the concentration of a solution in a substance.

Commercial oxygenated water is a solution of hydrogen peroxide in distilled water with a variable concentration between 3 and 30 %. This concentration is often used in term of volumes.

Materials:

•        Stand and clamp
•     Burette
•     Erlenmeyer
•      Pipette
•     100 mL volumetric flask
•     Potassium permanganate ( KMnO₄) 0.05 M
•     Commercial oxygenated water
•     Sulfuric acid 2 M

Procedure:

1. Arrange the burette in the stand with the clamp. Fill the burette with the potassium permanganate solution until level 0, be careful to not leave bubbles in the burette.
2. Make a solution of commercial oxygenated water taking 10 mL of it and pouring into a 100 mL volumetric flask with distilled water.
3. Take 25 mL of this solution using the pipette and pour it in the erlenmeyer, then, add 25 mL of 2 M sulphuric acid and 25 mL of distilled water
4. Titrate the mix (pour the mix) with the potassium permanganate solution until a slightly violet colour appears in the erlenmeyer.
5. Write down the volume needed and repeat the whole process again to verify the result.
6. Calculate the hydrogen peroxide concentration of the commercial oxygenated water and compare the result with the one on the commercial bottle.

2 or 3 minutes after finishing the experiment, the purple colour of the titration turned into an orange-brownish colour. Just like we can see on this images:

             

Bibliography:

McGraw-Hill Science & Technology Dictionary (n.d.), Redox titration, taken from:

http://www.answers.com/topic/redox-titration

Anne Marie Helmenstine (n.d.), Redox Titration Definition, taken from:

http://chemistry.about.com/od/chemistryglossary/a/redoxtitratdef.htm

EXPERIMENT n1 and n2: Analysis of elements and compounds

date of experiment: 15/1/2013

Experiment n1, n2: ELEMENTS AND COMPOUNDS

Background info:

We could learn many important things about elements: their chemical representation, their colour, their melting and boiling point, if they react with acid or not etc.

Aim:

In this experiment we are going to investigate nitric acid, potassium iodide hexane and Zinc in seventeen different points and represent all of them in a table. We will represent in a table all these kind of compounds and elements in the following various different aspects: 

Element/compound, chemical representation, smell (y/n - strong/light), color, shine, aggregation state, melting point, boiling point, magnetism, combustibility, conductivity,  solubility in water, solubility in organic solvents, r. vs. water, r. vs. OH-, r. vs. H+ and pH acq. sol.

Materials:

-  Nitric acid (60%)

-  Hexane

-  Zinc
-  Potassium Iodide

-  Hydrochloric acid (60%)

-  Bunsen burner 

-  Test tubes (x4)

-  Test tube holder

-  Goggles 

-  Lab coat

-  Thermometer

-  Magnet

-  Water

-  Organic solvent

-  pH indicator paper

-  Porcelain tray to test test the combustibility

-  An open circuit to test if they conduct electricity
-  Lighter

Procedure:
1.   Observing whether it is an element or compound is easy. Starting with nitric acid we know that is a compound containing hydrogen, oxygen and nitrogen atoms, so it is denominated a compound.

2.   We can see the chemical abbreviation in the bottle or we could formulate it. Is HNO3.


3.   The next step is  to test if it smells or not and if its a strong or light smell. In the case of an acid like nitric acid we need to open the bottle and with the hands move air towards our nose, this way we don´t damage senses. Yes, nitric acid smells lightly.

4.   Colour, this is easy, just drop some nitric acid in a test tube and analyze it. Nitric acid is colorless (Do not through away the content of the test tube, keep it in the test tube holder).

5.   Look at the test tube and see if it is shiny. Nitric acid does not shine.

6.   Look at the substance and see what its aggregation state is. Nitric acid aggregation state is liquid.

7.   To analyse the melting and boiling points, we need to research it on the internet fist to know if is possible to prove it. Nitric acid melting point is at -42ºC yet its boiling point is 83ºC so it is possible to determine it.
Set fire in the bunsen burner and introduce the thermometer in the test tube with nitric acid that we keep and determine the temperature in which starts to boil.

8.   To determine if its magnetic, pass the magnet near it and if the liquid is magnetic will follow the magnet. Nitric acid is not magnetic.


9.   Now we are determining if it is combustible adding some drops on the porcelain tray and carefully setting it alight. Nitric acid is combustible.

10.   Is it a conductor? We are introducing an open circuit to determine it, we introduce the two extremes (negative and positive) without touching each other. Nitric acid is not a conductor.

11.   To determine its solubility in water we introduce something more than a few drops of nitric acid and the same amount of water in a test tube. Yes, nitric acid is soluble in water.

12.   Repeat the process from step 11 but with an organic solvent (hexane). Yes it dissolves too without reacting.

13.   Repeat the process from steps 11 and 12 and see if it reacts. Yes it does.

14.   Now we are adding few drops of nitric acid in the porcelain tray and cutting a very small piece of litmus paper, we introduce it carefully in it and depending in the color that it turns we could see if is acidic (red), neutral or alkaline (blue). The paper with nitric acid turns pink, meaning that is acidic.

15.   Repeat the process with the others substances and make a table including all the results.


Video showing the combustibility of hexane:

Results:
Below, we can see the results obtained for each of the elements mentioned above organised in a table.

Now, we can see the results of our classmates, the elements that the students from our class used to perform the experiment.

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