Introduction: (Initial Observation)
Acids are highly reactive and can react with metals creating different salts and hydrogen. The reaction of acids and metals varies depending on the type of acid, it’s concentration and the temperature.
Diluted sulfuric acid easily reacts with Iron creating Iron Sulfate and releasing Hydrogen Gas; while the pure (100%) sulfuric acid is being shipped on Iron containers with no problem.
Although acids are very corrosive and react with many metals, they are often stored in tanks and pass through valves and pipes that are made of metals. How is this possible? The trick is that you must know what acids in what temperature and concentration can react with any specific metal.
In this project you will experiment the reaction of metals and acids under different conditions (temperature and concentration)
For your safety, wear goggles and rubber gloves. Perform experiments in a safe place, away from children, clothing and furniture. Counter top next to the sink and inside the sink might be a good place for your experiments. Adult’s supervision and Proper ventilation is required.
Gather information about acids-metals reactions. Read general chemistry books, magazines or ask professionals who might know in order to learn about acids-metals reaction. Keep track of where you got your information from.
Following are samples of information that you may find.
Why do acids react with metals?
Before you learn why some acids react with some metals, you need to understand the general structure of acid molecules. The molecules of each acid have two parts. One part is the acid radical and the other part is the acidic hydrogen. For example in H2SO4 (sulfuric acid), SO4 is the acid radical and H2 is the acidic hydrogen.
The correct way of writing these are SO4– for acid radical (sulfate ion) and 2H+ for two hydrogen ions.
The acid radical and hydrogen are bound together because of an attraction force between them. Such an attraction force may exist between a metal and an acid radical as well.
If the attraction force between a metal and acid radical is more than the attraction force between hydrogen and the acid radical, then the metal can displace the hydrogen.
The reaction of acids and metals are displacement reactions.
Displacement reaction is a reaction in which one element displaces another from a compound
Why do variations in attraction forces cause displacements?
Let’s say you have one weak magnet and a small nail. Your weak magnet can easily attract the nail since there are no surrounding stronger forces. Now put a second, stronger magnet next to the first weak magnet and the small nail. Naturally, the nail will be attracted to the stronger magnet. When you separate the two magnets, the nail remains attached to the stronger magnet. This shows how displacement may occur.
Need more examples?
Think about how attraction forces among people affect their decision in selecting friends. A sample of displacement reaction in human relations is when a young boy breaks up with his girlfriend when he meets a more attractive girl.
|What elements have a higher attraction force?Many metals have been classified based on their attraction force to acid radicals. A list of metals ordered by their attraction force is called a reactivity series. The non-metal hydrogen can be slotted into the Reactivity Series of metals below lead and above copper:
The metals above hydrogen in the Reactivity Series can react with with dilute acids, giving off hydrogen gas.
Those metals below hydrogen in the Reactivity Series do not react with dilute acids.
The purpose of this project is to discover the conditions that different acids react with different metals.
Students may select three of the following acids for their research:
- Sulfuric Acid
- Nitric Acid
- Hydrochloric Acid
- Acetic Acid
- Oxalic Acid
- Citric Acid
Also select at least 3 of the following metals:
Our independent variables are the concentration of acid, the temperature of reaction and the time length of the reaction. Our dependent variable is the rate of reaction that can be measured by the amount of hydrogen released or the amount of salt produced.
More heat and more concentration of acid results a faster or higher rate of reaction.
Experiments with acids must be performed outdoor or under a ventilated hood and in a well ventilated room. Always do your initial experiments with very small samples. Some acid metal reactions create poisonous fumes or harmful gasses.
Part 1: Effect of dilute acids at different temperatures:
In this experiment you test the effect of dilute acids on metals. For 3 acids and 3 metals, and 3 different temperature (cold, warm, hot) you will need to perform 27 experiments and record the results. The reaction time depends on the size of your samples. It can be as low as a few minutes up to a few hours. Whatever you choose, stay with that for all your 27 experiments. Also make sure that all your samples are the same size and shape or at least they have the same area in contact with acid. For This experiment use normal solution of acids. If you had more time and wanted to try higher concentrations, try 2 normal, 3 normal and more..
A normal solution of any substance, is a solution that contains one molecule gram of that substance per liter. For example one molecule gram of Sulfuric acid is 98 grams. So a normal solution of sulfuric acid is a 98 gram per liter solution.
For all the above reactions, place your metal sample in a test tube or beaker, add the acid and then bring it to the right temperature by inserting the tube or beaker in another container of water that can be cold, warm or hot.
The rate of reaction may be observed by the amount of hydrogen gas bubbles that form and release on the surface of each metal. It can also be measured by the mass of metal consumed during the reaction in a certain period of time.
consumed during the reaction in a certain period of time.
|Step 1: Metals (copper, Aluminum and Zinc) are added to the beaker.|
|Step 2: Dilute HCl acid is added to the beakers. Reaction with Zinc started immediately.|
|Step 3: After a while, all Zinc is used by the reaction, but aluminum is still releasing gas.
Here we did not change the temperature and allowed the reaction to continue at room temperature.
|Step 4: Aluminum is still releasing gas, but no reaction is observed in the two other beakers.|
You may do these experiments in test tubes. The level of metal and acid together on the test tube should not exceed one inch. In this way you will have extra room for foams and bubbles.
Note: If you don’t know the concentration of the acid that you buy, treat it as a strong acid. If you do the experiments in test tubes, you can use a pipette to add a few drops of acid on the metal and water already in the tube. Any strong acid mixed with the same weight water may be considered a dilute acid.
Materials and Equipment:
Material and equipment used for this experiment are as follows:
- 3 different acids
- 3 different metals
- Hot plate or electrical heater
- Beakers (One beaker for each metal)
- Protective devices such as goggles, rubber gloves,….
- Gram scale (Optional: You need this only if you want to measure the rate of reaction. Note that in this case all your metal samples must have the same surface area)
Where to buy:
Sulfuric acid is used in the car batteries. You can purchase it as Sulfuric acid or as battery acid from auto-parts dealers.
Hydrochloric acid also known as muriatic acid is used for cleaning concrete and tile. You can purchase it from hardware stores and cleaning supplies resellers.
Nitric acid is used by jewelers to test gold. Ask a local jeweler if there is any distributor in your area. Also suppliers of laboratory equipment and chemicals also sell nitric acid.
Oxalic acid is also a used for cleaning. You may find it trough hardware stores or suppliers of cleaning material.
Acetic acid is used in textile dye process, You can buy it from chemical stores or get vinegar that is 5% solution of acetic acid.
Citric acid is used as a food additive. Candy manufacturers use it to add a little sour taste to some candies. It is available in food grade from suppliers of food additives.
Metals such as Iron, aluminum, copper, lead and tin can be purchased from hardware stores. They are usually in the form of sheet, wire, strip, pipe and nail.
Tin wire is used for soldering, get the one that has no oil and no lead.
The body of cheap alkaline batteries is made of zinc. You may break down an old AA battery and remove its casing.
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.
You may need to calculate the normal concentration of different acids. For example you may buy a 100% sulfuric acid. In order to make a normal solution, you need to mix 98 grams of sulfuric acid with enough water to make it one liter. Remember you need to add sulfuric acid to the water, NOT WATER TO THE SULFURIC ACID.
If the acid that you buy is not 100%, then you need to do some calculations. For example if your acid is 70%, you divide 98 (98 is the molecular weight of sulfuric acid) by 70% and the result is 140. So you use 140 grams of this acid and add enough water to bring the total volume to 1 liter. (Because in 140 grams of a 70% Sulfuric acid, you have 98 grams of acid and the balance is water).
Another reason that you may need to do some calculations is that you may not want to make one liter acid, so you may want to use 49 grams acid and add enough water to bring the total volume to 500 milliliter.
Summary 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.
At this point you may need to do further studies so you can explain why the things happened the way they did. For example you may find out that the reactivity of a substance depends on its oxidation number or its location in periodic table. This may help.
How fast a reaction goes is called the rate of reaction. We can measure this by timing how quickly products are made. We can also time how quickly reactants are used up. The quicker these things happen, the faster the rate of the reaction.
Reactions happen when reactant particles collide. Changing the conditions makes them go faster.
For metals the reactivity increases as we move to the left and as we move down in the periodic table.
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.
Questions and Answers:
Q. What kind of acid is battery acid? Can it be used in this experiment?
A. Battery acid is sulfuric acid. It can be used for your experiments, however at the time of purchase or after that you need to find out if it is diluted or not and what is its percentage.
Q. What kind of acid is white vinegar? Can it be used in this experiment?
A. Vinegar is a 5% acetic acid. It can be used for your experiments.
Q. What would coca-cola do to metals?
A. Coca cola is mainly carbonic acid and can expedite rusting and corrosion in long term.
Q. I am using sulfuric, oxalic and hydrochloric acid for my experiments. How do I make a normal solution for these acids?
A. Normal solution is a solution that has one mole (molecule gram) of a substance in one liter. First find the molecular weight of your acid. For example the molecular weight of sulfuric acid is 98. Weight one mole of the acid, mix it with 1/2 liter of water and then add more water to bring the total volume to one liter. If your acid is not 100%, do a calculation to determine how much of that is equivalent to one mole of the 100% acid.
Also note that you should never add water to a strong sulfuric acid; instead you must add acid to the water.
Acid Treatment for decorative applications:
For decoration purpose, acid may be applied by brush, sponge or spray nozzles. Before starting the application, all other objects must be covered by plastics and masking tape. It may take many hours until you see the effect of each application. Acid treatment for decoration is usually performed on metals that have colorful salts such as nickel, copper and their alloys. For some applications, acid will then be neutralized by baking soda or ammonia. This can create colorful carbonates and hydroxides.
Picture shows a sample of copper metal treated with diluted nitric acid. Acid was applied using a sponge. It took about 3 days for the colors to form. Nitric acid was selected for this test because it is also a strong oxidizer and copper oxide has a nice blue/green color.
Acid treatment is better to be done before installation and the following guidelines may help to create a better result.
- Clean the metal surface with detergents to remove any grease or finger prints.
- Apply as little as possible acid in each application.
- If you spray the acid, use a spray gun with no metal parts.
- If your object can not be placed on a flat/ horizontal surface, you may need to add something to increase the viscosity of your acid solution.
- Do not re-apply acid until the result of previous application is fully dry and hard
- You may need to apply additional protective coating when the surface is ready and fully dry.