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Kinetics Experiments

Kinetics Experiments

Introduction: (Initial Observation)

During a chemical reaction, the concentration of reactants and the rate of reaction are changing continuously. The branch of chemistry that is concerned with the rates of change in the concentration of reactants in a chemical reaction is known as Kinetics.

Chemists collect and use the kinetics data (of any specific reaction) to determine the rate of reaction and control the rate of reaction as needed.

Two well known chemical reactions are the reaction of NaOH and HCl on aluminum.

Drano and other solid drain cleaners usually consist of NaOH, and a small amount of metallic aluminum. The aluminum reacts with NaOH to form hydrogen gas. The formation of gas bubbles provides a physical action that helps unclog a drain.

Anti-perspirants are made by the reaction of hydrochloric acid and aluminum.

In this project you will study the effect of concentration on the rate of reaction of HCl and NaOH with aluminum.

Dear 

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Information Gathering:

Find out what the chemical kinetics is and why it is important to chemists. Read books, magazines or ask a professional who might know in order to learn about the factors that may affect the rate of a chemical reaction.

Also study about the specific reactions that you are going to study. What are the products of your reaction and how can they be used?

Chemical kinetics is the study of the speed with which a chemical reaction occurs and the factors that affect this speed. This information is especially useful for determining how a reaction occurs.

What is meant by the speed of a reaction? The speed of a reaction is the rate at which the concentrations of reactants and products change.

Source…

Chemical kinetics deals with the rates of reactions. In order for a reaction to occur, a collision must occur; the collision must be of sufficient energy to break the necessary bonds and be of proper orientation. This is the basis of reaction rates. Factors effecting reaction rates are concentration of the reacting species found in the rate law, temperature and the presence or absence of a catalyst.

Source…

Chemical kinetics is the study and discussion of chemical reactions with respect to reaction rates, effect of various variables, re-arrangement of atoms, formation of intermediates etc. There are many topics to be discussed, and each of these topics is a tool for the study of chemical reactions. By the way, the study of motion is called kinetics, from Greek kinesis, meaning movement.

Source…

Reaction of Sodium Hydroxide and Aluminum:

Drano and other solid drain cleaners usually consist of lye, NaOH, and a small amount of metallic aluminum. The aluminum reacts with the lye solution to form hydrogen gas. The bubbling of the gas provides a physical action that helps unclog a drain. The reaction is:

2 Al(s) + 2 OH-(aq) + 6 H2O(l) —> 2 Al(OH)4-(aq) + 3 H2(g)

Another use of this reaction is cleaning aluminum. Most aluminum products such as sheets, wires, tubes and profiles are covered by some industrial oil. Caustic soda solution is used to remove the oil and other stains before painting, electro finishing or anodizing. (Paint is a protective layer for many metals. Many aluminum products are being anodized for protection. Anodizing forms a hard, protective layer of aluminum oxide on the surface of aluminum.)

Reaction of Hydrochloric acid and Aluminum:

Aluminum reacts with HCl solution to form hydrogen gas according to the following equation.

2 Al(s) + 6 H+(aq) —> 2 Al3+(aq) + 3 H2(g)

The above general reaction formula shows that Aluminum (Solid) reacts with Hydrochloric acid solution to produce aluminum salt and hydrogen gas. A more specific reaction formula can be written like this:

2 Al + 6 HCl —> 2 AlCl3 + 3 H2

The aluminum chloride solution produced in the above reaction (AlCl3 . 6H2O) is used in pharmaceuticals, cosmetics, antiperspirants, pigments, roofing granules, special papers, photography and textile (wool).

Drysol (brand name for aluminum chloride hexahydrate) is a prescription medication commonly prescribed for excessive sweating. A fairly common problem, excessive sweating can be limited to the armpits, but often affects the palms and soles of the feet as well. Once a person has tried several different kinds of over-the-counter antiperspirants without success, doctors often recommend Drysol.

Source…

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to determine the effect of concentration on the rate of reaction of Aluminum metal with Hydrochloric acid and Aluminum metal with caustic soda.

Chemists often need to control the rate of reactions for one of the following reasons.

  1. Slow chemical reactions reduce productivity, waste manufacturing resources and increase the overall cost of production.
  2. Fast chemical reactions may cause explosions, overflow reaction vessels and cause unsafe work environment.

Rate of reactions are often controlled by changing the reaction temperature or the concentration of reactants. Chemists need to perform many experiments for each specific reaction in order to determine the best or the optimal conditions for the reaction.

Controlling the rate of reactions in chemical factories is a task of chemical engineers who design and operate the production equipment. The gas stove that you have at home is a device to control the rate of reaction between gas fuel and oxygen from the air. In a gas stove the rate of reaction is controlled by a valve that limits the release of gas fuel.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

For the reaction of NaOH (Sodium Hydroxide) and aluminum:

Independent variable is the concentration of NaOH

Dependent variable is the rate of reaction

Controlled variables are temperature, method and procedures.

For the reaction of HCl (Hydrochloric Acid) and aluminum:

Independent variable is the concentration of HCl

Dependent variable is the rate of reaction.

Controlled variables are temperature, method and procedures.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following is a sample hypotheses:

The effects of concentration for NaOH and HCl are different because of differences in the activities of the two solutions.

For the reaction of NaOH and aluminum:

I think the rate of the reaction will increase by the initial increase in the concentration of the sodium hydroxide solution; however, after a certain point, increase in concentration may reduce the rate of reaction. My hypothesis is based on my gathered information about similar chemical reactions and the effect of water in increasing the rate of reaction. (For example in reaction of sulfuric acid and iron, adding water or diluting sulfuric acid increases the rate of reaction.)

For the reaction of HCl and aluminum:

I think the rate of the reaction will increase by initial increase in the concentration of hydrochloric acid. The highest concentration of acid is expected to provide the highest rate of reaction.

Experiment Design:

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: Aluminum and NaOH reaction rate

Introduction:

In this experiment you will study the effect of the concentration of NaOH solution on the rate of the reaction with aluminum.

Procedure:

  • In a small beaker or test tube, prepare a concentrated/saturated solution of NaOH by adding 10 mL water on about 6 grams of caustic soda. Ignore the solid NaOH that remains at the bottom of the test tube
  • Place a test tube in a firm support. Gently lay a small piece of foil across the test tube and with the bottom of a similar-sized test tube force the foil into the tube to form a basin-like depression. You may create such depression in other ways too.
  • Have a timing device ready. Carefully add 10 drops of the concentrated NaOH solution to the depression in the foil. Begin timing when the first drop hits the foil.
  • End the timing when there is evidence that a hole has formed in the foil. The solution may simply drop into the tube or a small hole may form with a drop of solution visible below the hole.
  • With forceps, carefully pick up the foil and rinse with water. Wrap in paper towel and place in trash can.
  • Repeat using a new piece of foil and test tube, but in this trial, place 2 drops of water on the foil and then add 8 drops of the NaOH solution. Start timing when the first drop of NaOH solution is added.
  • Continue using new pieces of foil and new test tubes with various dilutions of NaOH as listed in the table below.
Drops of Water Drops of NaOH solution

Time to form a hole

0 10
2 8
4 6
6 4
8 2

Prepare graphs of time (or rate which can be considered as 1/time) on the vertical axis and number of drops of NaOH solution on the horizontal axis.


Experiment 2: Aluminum and HCl reaction rate

Introduction:

In this experiment you study the effect of the concentration of HCl solution on the rate of the reaction with aluminum. (Remember that HCl is a gas, so we always use HCl solution as Hydrochloric Acid. Usually HCl is sold in a 36% solution)

Procedure:

  1. Prepare about 10 mL strong HCl solution. (about 20% HCl)
  2. Place a test tube in a firm support. Gently lay a small piece of foil across the test tube and with the bottom of a similar-sized test tube force the foil into the tube to form a basin-like depression.
  3. Have a timing device ready. Carefully add 10 drops of the strong HCl solution to the depression in the foil. Begin timing when the first drop hits the foil.
  4. End the timing when there is evidence that a hole has formed in the foil. The solution may simply drop into the tube or a small hole may form with a drop of solution visible below the hole.
  5. With forceps, carefully pick up the foil and rinse with water. Wrap in paper towel and place in trash can.
  6. Repeat using a new piece of foil and test tube, but in this trial, place 2 drops of water on the foil and then add 8 drops of the strong HCl. Start timing when the first drop of HCl solution is added.
  7. Continue using new pieces of foil and new test tubes with various dilutions of HCl as listed in the table below.
Drops of Water Drops of HCl solution

Time to form a hole

0 10
2 8
4 6
6 4
8 2

Prepare graphs of time (or rate which can be considered as 1/time) on the vertical axis and number of drops of HCl solution on the horizontal axis.


The following pictures show a sample setup for the above experiments

 

The pressure of the test tube forms a basin-like cavity on the aluminum foil. You may use other tools to form a basin like cavity.

 

 

 

 

 

The cavity on the aluminum foil must be large enough to hold 10 drops of water.

 

 

 

Start timing as soon as you place the first drop of hydrochloric acid or sodium hydroxide in the cavity.

 

 

 

 

 

 

An Styrofoam cup can serve as a base to hold the foil.

 

 

 

 

 

 

Watch for the first indication of a hole or the first drop of liquid that falls in the cup.

 

 

 

 

 

 

 

Place the cup where you can watch the cavity from both sides.

 

 

 

 

To form a cavity, you may also use a glass ball or the bottom of a test tube and use your hands to form the aluminum foil around that. Make sure that such forces are not changing the thickness of the aluminum foil.

Materials and Equipment:

Chemicals

  • saturated NaOH solution (about 13 g NaOH/25 mL distilled or deionized water) in small dropper bottle
  • 6 M HCl solution (50 mL concentrated HCl solution diluted to 100 mL with distilled or deionized water) in small dropper bottle
  • 5-square-centimeter pieces of aluminum foil

Equipment

  • test tubes
  • test tube support
  • clock which can measure seconds
  • forceps

Modifications/Substitutions :

  1. NaOH is available in grocery stores as lye.
  2. HCl solution is available from a hardware store as muriatic acid, 28% HCl. This solution is approximately 8 M and may be substituted for 6 M HCl solution.

Online stores:

Sodium Hydroxide (NaOH), Hydrochloric acid, pipettes and test tubes are also available at the following online stores:

www.ChemicalStore.com

www.klk.com

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.

Holding the pieces of aluminum foil with forceps, rinse with water, wrap in paper towel and place in solid waste. Solutions of NaOH and HCl may be flushed down drain with water.

Concentrated solutions of NaOH and HCl will burn skin and damage clothing. Fumes from acid may be caustic and/or irritating; carry out the reactions in a well-ventilated room (hood, if available). Do not mix the NaOH and HCl solutions; splattering may occur. Some splattering may occur near the end of the reaction of the NaOH or HCl with the aluminum; use care. Wipe up any splatters with wet paper towels. Goggles must be worn throughout the experiment.

Calculations:

No calculations are required for these experiments. You may perform some calculations to determine how you may dilute your HCl to a 6 Mol or to a 20% solution. If you do, please write your calculations in this section of your report. You can do this experiment with a very strong (36% or 10 M) solution of hydrochloric acid with similar results; however, a 20% solution has less fumes and is easier to handle.

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.

Conclusion:

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.

Use the results of your experiments to draw a conclusion. Describe the effect of the concentrations of NaOH and HCl on the rate of the reaction. Suggest a reason for why the two graphs might differ.

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.

Possible Errors:

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.

Note that aluminum foils have two sides. The rate of reaction may not be the same in both sides because of special coatings or other types of treatments. Make sure in all your experiments you use the same side of aluminum foil to start the reaction. It is also good to wash the aluminum foil with warm water and dish washing detergent prior to the experiment. Any oil remained on aluminum foil from the foil making process or from your hands may affect the results and delay the reaction.

References:

Visit your local library and find chemistry or chemical engineering books that study the reaction rate of some chemical reactions. Also find books and other publications that discuss production or use of sodium aluminates and aluminum chlorides.

Chemical Kinetics

Chemical Kinetics II

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