Introduction: (Initial Observation)
Water that is easily available in many places of the world, is a compound of hydrogen and oxygen gases. These two well known elements have many industrial applications.
In this project we will study the molecular structure of water and attempt to find out the ratio of hydrogen and oxygen in water.
Water plays an important role as a chemical substance. Its many important functions include being a good solvent for dissolving many solids, serving as an excellent coolant both mechanically and biologically, and acting as a reactant in many chemical reactions. Blood, sweat and tears… all solutions of water.
The simple statement that water is made from hydrogen and oxygen doesn’t give us a very clear picture of what really goes into the creation of a molecule of water. A quick look at the chemical equation for the formation of water tells us more.
2H2 + O2 = 2H2O
It takes two molecules of the diatomic hydrogen gas, combined with one molecule of the diatomic oxygen gas to produce two molecules of water.
Hydrogen is a gas with many applications. Hydrogen can be obtained in cylinders for experiments or industrial uses. Hydrogen is a highly flammable gas and creates a lot of heat energy while burning in oxygen. Hydrogen can also be used as a fuel. .
The process by which we generate hydrogen (and oxygen) from water is called electrolysis. The word “lysis” means to dissolve or break apart, so the word “electrolysis” literally means to break something apart (in this case water) using electricity.
Electrolysis is very simple – all you have to do is arrange for electricity to pass through some water between to electrodes placed in the water, as shown in the diagram above. Its as simple as that! The principle of electrolysis was first formulated by Michael Faraday in 1820.
Hydrogen, H2, is the simplest element. It is the first element in the periodic table, and it is placed in Group I of the periodic table. It has three Isotopes
- Atomic Number : 1
- Atomic Mass : 1.008
- Melting Point : -259 degC
- Boiling Point : -253 degC
- Density : 0.09
Hydrogen can be purchased in large industrial cylinders.
Before collecting hydrogen great care must be taken to ensure that all the air has been displaced from the apparatus since a mixture of hydrogen with air is highly explosive.
The purpose of this project is to experiment producing hydrogen and oxygen by electrolysis of water. We will attempt to find out the ratio of hydrogen to oxygen and solve other problems that may raise during the experiments. For lower grades, you will not need to define questions, however if you want to do so, you can select from the following questions:
1 _ What is the ratio of hydrogen and oxygen in water?
2 _ What water temperature optimizes the electrolysis of water?
3 _ What electrical voltage optimizes the electrolysis of water?
Electrolysis is optimized when the highest amount of gas is produced in least amount of time.
You need to identify variables only if you have selected one of the above questions, otherwise you can skip this section.
If you have selected question 2 above, temperature will be your independent variable. For question 3, voltage will be your independent variable. In both cases the amount of produced hydrogen or the amount of produced oxygen will be called dependent variables.
Based on your gathered information, make an educated guess about the result of your experiment, for example the voltage or temperature that yields the best result.
For question number 2 a possible hypothesis is: Electrolysis of colder temperature water yields a better result.
For question number 3 a possible hypothesis is: Higher voltages yields better result.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment 1: Simple Electrolysis
In this experiment we use a 6 volt battery, some wires and two pencils (as electrodes) to pass electricity through salt water.
- Remove the erasers and their metal sleeves from both pencils, and sharpen both ends of both pencils.
- Fill the glass with warm water.
- Attach wires to the electrodes of a battery, and the other ends to the tips of the pencils, as shown in the picture above. It is important to make good contact with the graphite in the pencils. Secure the wires with tape.
- Punch small holes in the cardboard, and push the pencils through the holes.
- Place the exposed tips of the pencils in the water, such that the tips are fully submerged but are not touching the bottom, and adjust the cardboard to hold the pencils.
- Wait for a minute or so: Small bubbles should soon form on the tips of the pencils. Hydrogen bubbles will form on one tip (associated with the negative battery terminal – the cathode) and oxygen from the other.
With this setup your initial tool for water electrolysis is ready, but this setup is not enough to collect hydrogen or oxygen.
Experiment 2: Better design for Electrolysis
In order to collect the hydrogen and oxygen gases and see the ratio of these gases produced by water hydrolysis, you can use this experiment design.
Fill up to 1/2 of a beaker or cup with saltwater.
Fill up two test tubes with salt water, hold their top with your finger, turn them upside down and insert in the beaker or the cup. Make sure no air enters any of the test tubes. If you cant use your finger to do this, use a piece of paper as described below.
After you fill up a test tube, you can cover it with a piece of paper. Hold the paper and turn the tube upside down. Now the air pressure should support the paper and the water in the tube. Insert the tube into the water and then remove paper.
By now you should have two test tubes filled with salt water, upside down in the cup of salt water.
Prepare the wire that you are going to use as electrodes. Insulated steel wires or insulated aluminum wires are good choices, if these are not available, use insulated solid copper wire instead.
Remove the insulation of about 2 inches of wires from each end. You will need two pieces of wire about one foot each
Since the wire that we are using here is too thin, we are making a coil out of the end that enters the test tube so it will have a larger surface of contact with water and produce more gas.
Carefully insert one wire in each test tube and connect the other end of the wires to the battery.
If you are using a 6 volt battery known as lantern battery, you should see release of gases very soon. With smaller batteries it will take more time for gases to appear.
At this time test tubes are laying against the sides of beaker. If you want them to stand vertically, you can use a piece of cardboard as support.
You will not have to remove test tubes from the water. Just push the cardboard with holes over the test tubes.
Question: I have run the experiment using the two test tube approach. I used cold water with a teaspoon of salt and a 6-volt lantern battery. In two attempts (one with salt and one without), I have easily collected a good amount of hydrogen gas in the – tube, but the + tube does not seem to collect any oxygen gas. I am at a stopping point as I have no clue what the problem is. Please advise. Thank you.
Answer: In the experiment that you did not use salt, the oxygen is being consumed right there by oxidizing your positive electrode. You may have noticed color change or brown rust on positive electrode. If that is the case, you are not using stainless steel. Try to use stainless steel, aluminum or graphite from a pencil for better results.
In the experiment with salt water, you are getting chlorine gas in the positive electrode and that dissolves back into the solution. With salt in the solution, salt will break down to sodium metal and chlorine gas. Sodium metal immediately reacts with water and releases hydrogen gas and produces sodium hydroxide. Sodium hydroxide and chlorine gas in the solution react with each other and become sodium hypo chloride. This is also known as bleach and is sold with trade names such as Clorox.
Question: How can we show the collected gases in test tubes are Oxygen and Hydrogen?
Answer: Hydrogen burns with a clear blue flame and produces water; however, the best indication of hydrogen is a pop sound that it makes when you bring a small flame to the mouth of the tube.
To verify oxygen, lit a wood splint; drop the splint in the test tube or jar containing pure oxygen; The flame flares up even more brightly, and the splint burns much more rapidly than it would in normal air.
Question: I am not getting many bubbles. Is it because I am using a contractor pencil instead of a number 2 pencil?
Answer: Contractor pencils are better because they have more lead (graphite) that is the conductive part of a pencil. If you did not get enough bubbles it may be due to a low voltage battery or low conductivity of the water. Make sure you are using a large 6-volt battery. Also add a few drops of battery acid to the water to make it more conductive. Battery acid is sulfuric acid.
Materials and Equipment:
- A battery or DC power supply with a voltage greater than 1.5 volts – 6 volts and 9 volts, batteries work well.
- Two pieces of solid electrical wire about a foot long.
- A pair of lead wires with alligator clips on each end. (optional)
- Two number 2 pencils to be used as electrodes
- A jar full of tap water
- small piece of cardboard
- electrical or masking tape
Tools you will need
- pencil sharpener (an exacto knife will do if a sharpener is unavailable)
- wire strippers or scissors, if the wires are insulated.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
No calculations are required.
Summery of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.