acids and bases experiment hypothesis

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Acid-Base Chemistry

Acid-base chemistry is a fundamental aspect of chemical science that plays a crucial role in our daily lives. Its applications range from industrial processes to biological systems. Understanding acid-base chemistry is not just essential for scientists, but also for everyday life, as it helps in making informed decisions about health, nutrition, and environmental issues.

Acids and Bases: Definitions

Acids and bases are two types of compounds that readily react with one another.

• Acids are substances that donate protons (H⁺ ions) or accept electron pairs. Common examples include vinegar (acetic acid, CH₃COOH), citrus fruits (citric acid, C₆H₈O₇), and stomach acid (hydrochloric acid, HCl). The properties of acids include a sour taste, ability to turn blue litmus paper red, and corrosiveness.
• Bases , on the other hand, are substances that accept protons or donate electron pairs. Examples include baking soda ( sodium bicarbonate , NaHCO₃), soap (sodium hydroxide, NaOH), and ammonia (NH₃). Bases are characterized by a bitter taste, slippery feel, and the ability to turn red litmus paper blue.

Acid-Base Chemistry and the pH Scale

The pH scale , ranging from 0 to 14, measures the acidity or alkalinity (basicity) of a solution. A pH less than 7 indicates acidity, while a pH greater than 7 indicates alkalinity. A pH of 7 is neutral. Pure water is an example of a substance with a neutral pH.

Acid-Base Chemistry Theories

The three main theories of acids and bases are the Arrhenius theory, Brønsted-Lowry theory, and Lewis theory. Each of these theories has its uses in chemistry.

• Acids : Substances that increase the concentration of H⁺ ions in water.
• Bases : Substances that increase the concentration of OH⁻ ions in water.
• Acids : Proton donors.
• Bases : Proton acceptors.
• Acids : Electron pair acceptors.
• Bases : Electron pair donors.

Strength of Acids and Bases

One way of classifying acids and bases is as strong or weak:

• Strong Acids and Bases : These dissociate completely in water. Examples include hydrochloric acid (HCl) and sodium hydroxide (NaOH).
• Weak Acids and Bases : These partially dissociate in water. Examples include acetic acid (CH₃COOH) and ammonia (NH₃).

Acid-Base Reactions and Neutralization

Acid-base reactions typically involve the transfer of protons from acids to bases. Neutralization is a specific type of acid-base reaction where an acid and a base react to form water and a salt , effectively neutralizing each other.

The outcome of an acid-base reaction depends on the strength of the acids and bases.

• Strong Acid with Strong Base : This leads to complete neutralization, forming a neutral salt and water. Example: HCl (acid) + NaOH (base) → NaCl (salt) + H₂O (water).
• Strong Acid with Weak Base : The resulting solution is slightly acidic, as the weak base cannot completely neutralize the strong acid. Example: HCl (acid) + NH₃ (base) → NH₄Cl (salt) + H₂O (water).
• Weak Acid with Strong Base : The resulting solution is slightly basic, as the strong base completely neutralizes the weak acid. Example: CH₃COOH (acid) + NaOH (base) → CH₃COONa (salt) + H₂O (water).
• Weak Acid with Weak Base : This leads to partial neutralization, with the pH of the resulting solution depending on the relative strengths of the acid and base. Example: CH₃COOH (acid) + NH₃ (base) → CH₃COONH₄ (salt) + H₂O (water).

Buffers in Acid-Base Chemistry

A buffer is a solution that resists changes in pH when small amounts of an acid or a base are added. This property is essential in various chemical, biological, and environmental contexts where maintaining a stable pH is critical.

Buffers typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. This dual presence allows the buffer to neutralize added acids or bases. For instance, in a buffer composed of acetic acid (CH₃COOH) and its conjugate base, sodium acetate (CH₃COONa), the acetic acid neutralizes added bases while the sodium acetate neutralizes added acids.

The buffer capacity refers to the amount of acid or base a buffer solution can absorb without a significant change in pH. This capacity depends on the concentration of the buffer components and the closeness of the solution’s pH to the pKa (acid dissociation constant) of the buffer acid.

Frequently Asked Questions (FAQs) on Acid-Base Chemistry

What is the difference between a strong acid and a weak acid?

• A strong acid completely dissociates into its ions in water, releasing all of its hydrogen ions. Examples include hydrochloric acid (HCl) and sulfuric acid (H₂SO₄). A weak acid only partially dissociates in water, leaving many of its hydrogen ions un-released. Acetic acid (CH₃COOH) and citric acid (C₆H₈O₇) are common examples.

Can you explain what a pH of 7 means?

• A pH of 7 is neutral, meaning the solution is neither acidic nor basic. It indicates a balance between hydrogen ions (H⁺) and hydroxide ions (OH⁻) in water. Pure water at 25°C (77°F) has a pH of 7.

Why is pH important in daily life?

• pH plays a crucial role in everyday life. It affects food taste, digestion, skin health, pool water safety, garden soil quality, and even the functioning of batteries and car fluids.

What are some common household acids and bases ?

• Common household acids include vinegar (acetic acid), lemon juice (citric acid), and battery acid (sulfuric acid). Household bases include baking soda (sodium bicarbonate), bleach (sodium hypochlorite), and ammonia-based cleaners.

How do buffers work?

• Buffers work by using a weak acid and its conjugate base (or a weak base and its conjugate acid) to resist changes in pH. When you add an acid or base to the buffer, the buffer components react to neutralize the added substance. This keeps the pH relatively stable.

What is an acid-base neutralization reaction?

• An acid-base neutralization reaction occurs when an acid and a base react to form water and a salt. This reaction typically decreases the solution’s acidity or basicity.

How are acids and bases used in industries?

• Acids and bases have wide industrial applications. Acids find use in metal processing, fertilizer production, and petroleum refining. Bases are important in soap and detergent manufacturing, textile processing, and papermaking.

What safety precautions should be taken when handling acids and bases?

• When handling acids and bases, wear protective gear, work in a well-ventilated area, and be aware of proper storage and disposal methods. Avoid skin contact and inhalation of fumes. In case of spills, neutralize the acid or base and clean up the spill safely. Always have a first aid kit and emergency protocols in place.
• Finston, H.L.; Rychtman, A.C. (1983).  A New View of Current Acid-Base Theories . New York: John Wiley & Sons.
• Masterton, William; Hurley, Cecile; Neth, Edward (2011).  Chemistry: Principles and Reactions . Cengage Learning. ISBN 978-1-133-38694-0.
• Paik, Seoung-Hey (2015). “Understanding the Relationship Among Arrhenius, Brønsted–Lowry, and Lewis Theories”.  Journal of Chemical Education . 92 (9): 1484–1489. doi: 10.1021/ed500891w
• Petrucci, R. H.; Harwood, R. S.; Herring, F. G. (2002).  General Chemistry: Principles and Modern Applications  (8th ed.). Prentice Hall. ISBN 0-13-014329-4.

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Science Projects > Chemistry Projects > Acid Base Reactions & pH Experiments  

Acid Base Reactions & pH Experiments

Experimenting with acids and bases can make for exciting chemistry projects!

Acidic solutions have a higher concentration of hydrogen ions (H+).

These are hydrogen atoms that have lost an electron and now have just a proton, giving them a positive electrical charge.

Basic solutions, on the other hand, contain hydroxide ions (OH-). One of the simplest activities to show how acids and bases react with each other (and to demonstrate their different properties) is to make a vinegar and baking soda volcano .

For another reaction experiment , put an Alka-Seltzer tablet in the bottom of a clear plastic film canister (the kind where the cap fits inside instead of closing over the outside).

Fill the canister with warm water and then quickly put the cap on and watch the acid-base reaction!

The pH scale is used to measure how acidic or basic a solution is. Acids have a pH below 7; bases have a pH above.

Neutral solutions (like distilled water) with a balanced number of H+ and OH- ions have a pH of 7. Do the following projects to explore the cool effects of pH.

Litmus is a natural acid-base indicator extracted from a type of lichen. If you have red and blue litmus paper , you can test different solutions for whether they are acids or bases.

Blue litmus paper turns red when a solution is acidic; red litmus paper turns blue in basic solutions.

Try testing window cleaner, toilet bowl cleaner, orange juice, and apple juice—pour a little of each into separate test tubes or small glasses or jars.

Use the litmus paper to determine which are acids and which are bases. Here are the pH levels of some other substances that you might test:

• Lemon juice (2)
• Vinegar (3)
• Egg whites (8)
• Baking soda (9)
• Ammonia (10)

Human blood has an ideal pH of 7.4; even slight fluctuations can seriously affect our bodies.

You can also make your own pH indicator —use a blender to mix one part chopped red cabbage with two parts boiling water and use the juice to test different solutions.

Acids will turn the pigments in the indicator to a reddish color; bases will turn the pigments bluish or yellow-green.

Mystery Pitcher

Make ordinary water turn bright pink and then back to clear! This makes a great “magic trick” to impress your friends – just be careful no one mistakes it for fruit punch and drinks any!

>> Check out our project video to see this trick in action!

What You Need:

• Phenolphthalein solution
• Sodium carbonate
• 5 glasses and a non-see-through pitcher of water

What You Do:

1. In the first glass put a little less than 1/8 teaspoon of sodium carbonate, in the second put 6 drops of phenolphthalein solution, and in the third put three droppers-full of vinegar.

2. Add a few drops of water to the first glass and stir to dissolve the sodium carbonate.

3. Fill all the glasses with water from the pitcher, then pour all of them back in the pitcher except for the glass with vinegar.

4. Refill the remaining four glasses – the water will be red!

5. Now pour all five glasses back in the pitcher. Refill the glasses one last time—the liquid will be colorless again!

What Happened:

Phenolphthalein is a pH indicator, but it only turns colors in reaction to bases. When you poured the four glasses back into the pitcher, the phenolphthalein reacted to the sodium carbonate, a base, and turned the solution to bright pink “kool-aid.” To change it back to “water,” all you had to do was add the acidic vinegar, which turned the phenolphthalein colorless again.

Rainbow Reaction Tube

Amaze your friends by mixing two solutions to make a rainbow!

Watch as purple sinks to the bottom and red floats to the top, and they mix together to form every color in between.

• 10ml graduated cylinder
• Universal indicator
• Distilled white vinegar

2. Add 3 drops of vinegar to the solution in the graduated cylinder, and it should turn red.

3. In a beaker, put two scoops of sodium carbonate and then add about 30 ml of water. Mix together with the stirring rod until the sodium carbonate dissolves. The solution should be clear.

4. To start the reaction, fill one dropper full with sodium carbonate solution. Squeeze the dropper into the graduated cylinder quickly, rather than drop by drop. The clear solution should instantly turn dark purple, and slowly sink to the bottom, swirling around to make the rainbow.

5. Let the contents of the cylinder settle, until you can see each color from bluish-purple to red. To make the rainbow disappear, pour it into an empty beaker, and it should turn yellow or yellowish green.

Universal indicator changes colors to show the pH level of a substance. In this case, when you mixed an acidic solution (vinegar) with a basic one (sodium carbonate), the indicator made a colorful spectrum — from dark blue to red. Interestingly, if you had added the solutions in the opposite order, you would not have seen a rainbow. To get the rainbow effect, another scientific principle is at work— density . The sodium carbonate solution you made is denser than the indicator solution, so it sinks to the bottom. As the sodium carbonate solution makes its way to the bottom, some of its molecules mix with vinegar molecules, making a new solution, which shows up as a color of the pH scale.

If you don’t turn the graduated cylinder upside down, the rainbow will last several days. Over time the colors will mix together through the process of diffusion. The molecules of each solution will mix throughout the graduated cylinder, rather than staying concentrated at the top or bottom. Once you mix the acid and base solutions together, the solution will be pH neutral, and look yellow or slightly green.

To make a different kind of rainbow tube, try making this rainbow density column with all household materials.

More Chemistry pH Projects:

• Green Eggs & Ham
• Fizzy Bath Bombs
• Acid & Apples
• Copper-Plated Nails

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Simple Acids and Bases Science Experiment to Do With Kids

Learning , Science | 1 comment

Looking for a fun science experiment to do with kids with ingredients you have at home? Try this acids and bases experiment to test household solutions and decided if they are acidic or basic. 

I’ve always loved chemistry. I was the kid who asked for a chemistry set for Christmas and spent hours randomly mixing things in my bedroom. 

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As a parent, I still love it! And I love doing fun experiments with my kids and watching them think through their guesses and see their amazement the first time they see certain reactions. 

This is a simple chemistry experiment to do with your kids. It doesn’t require fancy ingredients- and you probably already have most of them on hand already!

Directions to Conducting an Acids and Bases Experiment with Kids

The basis of this experiment is to find out which solutions are basic and which are acidic. The amount of background information you give to your kids will depend on their ages and ability to comprehend.

It’s okay to talk in simple terms and in language and examples that they can understand. 

I will add a section to the bottom of this article giving a little more information about acids and bases and how you can help your kids understand the difference. But for now, let’s get on to the science experiment!

Step 1: Make Turmeric Paper

The first thing you need to do is make turmeric paper. This is what you will use to test your solutions on to tell you if they are acids and bases. 

To make turmeric paper you will need:

• 1/4 tsp powdered turmeric
• 1/4 cup rubbing alcohol
• coffee filters

Mix the alcohol and the turmeric is a bowl. Make sure it’s well mixed. 

Dip the coffee filters in the mixture until they are completely saturated and very yellow in color. 

Set the filters aside to dry- either hang them up or just set them on a cookie sheet or tray.

Step 2: Gather Your Supplies

While the filters are drying, gather the rest of your supplies. Here’s what you’ll need:

• a variety of solutions* (see below for ideas)
• test tubes or small jars to hold your solutions
• droppers/pipettes
• a tray (or pan) to contain mess
• Paper or white board to record observations

Not sure what kind of solutions to try? Here are a few ideas:

• lemon juice
• fruit juices
• urine (if you’re really adventurous!)
• borax water
• baking soda water
• sugar water
• all purpose cleaner

You get the idea. Basically anything liquid or that can be mixed with liquid to create a solution. Raid the fridge, cabinet, and bathroom for ideas!

Let your kids have fun with choosing solutions to test. That’s part of the fun of doing science experiments with kids!

*Note: You might be surprised at how many things are acidic. Make sure you have at least a couple basic solutions so you have red strips to test for acids. Baking soda water is a good base. 

Step 3: Make Your Guesses (Hypothesis)

Making the hypothesis is an important part of every science experiment- even if you are doing an experiment with very young kids. 

Give a little background information on what acids and bases are- I’ll get to that at the bottom of this article.

Then explain what you are going to be doing- deciding which solutions are acids and which are bases.

And finally, have your kids make guess as to what will happen and what the outcomes will be. 

Write all of this down and then you can see how right you are!

Step 4: Test Acids and Bases

Now that you have all of your supplies, let’s get this experiment started!

Start by cutting your coffee filters into strips. They don’t have to be very big to conduct this experiment…just 2-3 inches long and an inch or less wide. Just make sure you have enough to test all of your solutions! 

The basic experiment runs like this:

• Choose a solution
• Place a test strip on your tray
• Use a pipette to drip a drop or 2 of the solution on the test strip
• Watch for a change in color

If the color of the test strip changes from yellow to red, your solution is a base! Write that observation down somewhere so you can keep track of which solutions are basic and which are acidic. 

If you don’t see a color change- make a note of it and we’ll come back around and do more tests to see if we have an acid or a neutral solution. 

Coffee didn’t turn the yellow strip red, but it did turn a red one back to yellow. It’s an acid!

Once you have done all of your solutions one time, it’s time to circle back around to all the solutions that are not basic and didn’t produce a color change. 

For this part of the experiment, you want to test your remaining solutions on the strips that are ALREADY RED- meaning the ones you tested basic solutions on. 

If your strip STAYS red, your solution is neutral. 

If your strip turns back to YELLOW, your solution is an acid. 

Write down your observations and create a list of neutral, basic, and acidic solutions. 

At this point your kids may want to keep going. I know mine went back to the kitchen and bathroom to grab more solutions to test!

*Note: Be aware of cross contamination. Be sure to keep your strips apart from each other and your rinse your pipettes before using in new solutions. We had to wash our trays a couple of times as we kept testing solutions to keep everything separate!

Top: Base turned the strip red; Bottom: Acid turned the strip back to yellow

Step 5: Results

Don’t just do a science experiment and leave without really looking at the information you learned!

By now you should have a paper or white board covered in both you hypothesis (guesses) and your actual results. 

Where you correct? 

Were you surprised by any of the results?

Can you research your results and see if the experiment went wrong at any point and provided inaccurate results?

More on Acids and Bases:

As I mentioned, the amount of background information will depend on the ages of your kids. But here’s a little more about acids and bases and how you can help your kids understand what they are.

Let’s start with the definitions:

• Acids (Acidic Solution): A substance that can donate a hydrogen ion or proton and has a pH of less than 7. 
• Bases (Basic Solution): A substance that can accept a hydrogen ion and has the pH of more than 7. 
• Neutral: A substance that is neither acid or basic and has a pH of 7.
• pH Scale: The scale that measures how acidic or basic a solution is. It runs from 0-14, with 0 being the most acidic and 14 being the most basic. 

It can be helpful to talk about acids and bases in terms you kids might already know. 

Talk about things like stomach acid, acid rain, acid like they might see in cartoons that “burns”.

You can also talk about some of the characteristics of acids and bases. Such as:

• Sour tasting
• Can feel tingly on the skin
• Can corrode metal
• Bitter tasting
• Slippery or soapy feeling on the skin

You can also note that acids and bases help to neutralize each other. 

And on a final note, be sure to note that there are varying degrees of acids and bases and that you should always exercise caution when dealing with them since both strong acids and bases can cause skin irritation. 

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great work thank you for sharing I will try with my kids

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• Acids, Bases and Salts
• Red Cabbage Indicator

Red cabbage Indicator

Red cabbage indicator is a purple-coloured solution that is used to test whether substances are acid or base . Red cabbage that is often found in homes can be used to prepare a solution that acts as a pH indicator. The cabbage basically contains a pigment molecule called flavin or anthocyanin that changes colour depending on the acidity of the solution.

Normally, the purple solution turns red in colour when it combines with something acidic and it turns bluishg-green in colour when it combines with a base. If the substance does not cause the colour to change then it is mostly neutral.

Red Cabbage Indicator pH Colours

Below are the different pH levels and the colours that are obtained during the red cabbage indicator test.

Let us conduct an experiment and observe the results.

To determine which chemicals are bases and which are acids.

Apparatus Required

• Red cabbage leaves
• Lemon juice
• Soda(baking soda)
• Glass jars of a similar size
• Cut the cabbage leaves into small pieces.
• Boil separate cups of water as they will be required to submerge your pieces later on.
• Place the cabbage pieces into a bowl and pour the water in the bowl. Keep it for several minutes so that the cabbage pieces get soaked. You can also use a mixer to grind the leaves and obtain a solution.
• If you are not using the mixture then separate the juice from the leaves.
• Take glass jars and place them about two inches apart. Pour every chemical (lemon juice, vinegar, detergent and soda) into each jar.
• Now to determine whether the substance is a base or an acid pour the cabbage juice into each jar. Here, if the mixture turns pink or red the chemical is an acid and if it turns bluish-green the chemical is usually a base.

This experiment can easily be conducted even in the house and can be used to test different substances which are easily available.

Safety Tips

•  Since the chemical indicator is used to test acids and bases it is always advised to use safety goggles and gloves especially while dealing with strong or concentrated chemicals.
• Chemicals can be washed down the drain safely with water.
• A neutralisation experiment can also be done along with the test.

Making pH Paper

In addition to the solution, pH paper strips can also be created using red cabbage using the steps given below: 1. Firstly, use a filter paper (or coffee filter) and dip it in the concentrated solution obtained from red cabbage.

2. Soak it for some time and later take the paper and dry it.

3. Once it is dried, cut the paper into small strips and they are ready to be used for testing the pH of different solutions.

4. Pour a drop of liquid on the test strip and see what colour is obtained. The strip also turns either red or green depending on whether it is acidic or basic.

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Lemon chemistry: an acid base experiment.

Kari Wilcher runs a great blog. She was looking to teach her pre-school children about the Scientific Method while trying out some kitchen chemistry at the same time. Her plan was to show a dramatic acid-base reaction using lemons, baking soda, and a little dish soap. She writes:

“I firmly believe that children are never too young to be exposed to the scientific method and should follow it. I have found that the scientific method is very easy for them to understand, and follow, when presented to them in a simple way. I like to use a rebus (picture) to help my non-readers understand the directions. I also use these “big” words: data, hypothesis, prediction, and observation. We, including Momma, wear goggles (from the dollar store) and a lab coat (a.k.a. dad’s white button up shirt) because we are real scientists doing real science experiments…and it just makes us cool.”

You will need:

• Fresh Lemons
• A small measuring cup & measuring spoon
• Baking Soda
• Liquid dish soap
• A clear cup for the reaction

What to do:

• Roll the lemons on the counter like dough. This releases the juice inside the lemon.
• Cut the lemon in half (adults only, please) and carefully squeeze out the juice into a small measuring cup. Note how much juice was created from each lemon and put the juice aside.
• Into the empty glass place 1 Tablespoon of baking soda.
• Add 1 teaspoon of liquid dish soap to the baking soda. Stir these up a bit.
• Pour the lemon juice into the cup and stir. Now watch the lemon suds erupt!

How does it work? This is a classic example of an acid-base reaction. This is often done with vinegar and baking soda, but we liked Kari’s “lemon twist.” The baking soda (a base) and the lemon juice (an acid) combine to release Carbon Dioxide gas. The liquid soap turns the bubbles into a foam that often erupts right out of the glass.

Try it out and let us know how it goes!

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Biology archive

Course: biology archive   >   unit 3, autoionization of water.

• Arrhenius acids and bases
• Brønsted–Lowry acids and bases
• Definition of pH
• Introduction to buffers

Acids, bases, pH, and buffers

• Acids, bases, and pH

Introduction

• An acidic solution has a high concentration of hydrogen ions (H + ‍   ), greater than that of pure water.
• A basic solution has a low H + ‍   concentration, less than that of pure water.

Acids and bases

The ph scale, attribution:, works cited:.

• Acids and bases. (2015). In Your Mother Was a Chemist . Retrieved from http://kitchenscience.sci-toys.com/acids .
• Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). Acidic and basic conditions affect living organisms. In Campbell Biology (10th ed., p. 51). San Francisco, CA: Pearson.
• Brindza, P. (n.d.). How many atoms are in the human head? In Jefferson lab . Retrieved from http://education.jlab.org/qa/mathatom_03.html .

Additional references:

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Effect of Acids and Bases on the Browning of Apples

Everything You Need for This Simple Experiment

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Apples and other fruit will turn brown when they are cut and the enzyme contained in the fruit (tyrosinase) and other substances (iron-containing phenols) are exposed to oxygen in the air.

The purpose of this  chemistry laboratory exercise is to observe the effects of  acids and bases  on the rate of browning of apples when they are cut and the enzymes inside them are exposed to oxygen.

A possible hypothesis for this experiment would be:

Acidity (pH) of a surface treatment does not ​affect the rate of the enzymatic browning reaction of cut apples.

Gather Materials

The following materials are needed for this exercise:

• Five slices of apple (or pear, banana, potato, or peach)
• Five plastic cups (or other clear containers)
• Vinegar (or dilute acetic acid )
• Lemon juice
• Solution of baking soda ( sodium bicarbonate ) and water (you want to dissolve the baking soda. Make the solution by adding water to your baking soda until it dissolves.)
• Solution of milk of magnesia and water (ratio isn't particularly important - you could make a mixture of one part water one part milk of magnesia. You just want the milk of magnesia to flow more readily.)
• Graduated cylinder (or measuring cups)

Procedure - Day One

• Lemon Juice
• Baking Soda Solution
• Milk of Magnesia Solution
• Add a slice of apple to each cup.
• Pour 50 ml or 1/4 cup of a substance over the apple in its labeled cup. You may want to swirl the liquid around the cup to make sure the apple slice is completely coated.
• Make note of the appearance of the apple slices immediately following treatment.
• Set aside the apple slices for a day.

Procedure and Data - Day Two

• Observe the apple slices and record your observations. It may be helpful to make a table listing the apple slice treatment in one column and the appearance of the apples in the other column. Record whatever you observe, such as the extent of browning (e.g., white, lightly brown, very brown, pink), the texture of the apple (dry? slimy?), and any other characteristics (smooth, wrinkled, odor, etc.)
• If you can, you may want to take a photograph of your apple slices to support your observations and for future reference.
• You may dispose of your apples and cups once you have recorded the data.

What does your data mean? Do all of your apple slices look the same? Are some different from others?

If the slices look the same, this would indicate that the acidity of the treatment had no effect on the enzymatic browning reaction in the apples. On the other hand, if the apple slices look different from each other, this would indicate something in the coatings affected the reaction.

First, determine whether or not the chemicals in the coatings were capable of affecting the browning reaction .

Even if the reaction was affected, this does not necessarily mean the acidity of the coatings influenced the reaction. For example, if the lemon juice-treated apple was white and the vinegar-treated apple was brown (both treatments are acids), this would be a clue that something more than acidity affected browning.

However, if the acid-treated apples (vinegar, lemon juice) were more/less brown than the neutral apple (water) and/or the base-treated apples (baking soda, milk of magnesia), then your results may indicate acidity affected the browning reaction.

Conclusions

You want your hypothesis to be a null hypothesis or no-difference hypothesis because it is easier to test whether or not a treatment has an effect than it is to try to assess what that effect is.

Was the hypothesis supported or not? If the rate of browning was not the same for the apples and the rate of browning was different for the acid-treated apples compared with the base-treated apples, then this would indicate that the pH ( acidity, basicity ) of the treatment did affect the rate of the enzymatic browning reaction. In this case, the hypothesis is not supported.

If an effect was observed (results), draw a conclusion about the type of chemical (acid? base?) capable of inactivating the enzymatic reaction.

Additional Questions

Here are some additional questions you may wish to answer upon completing this exercise:

• Based on your results, what substances in each apple treatment affected the enzyme activity responsible for the browning of the apples? Which substances did not appear to affect the enzyme activity ?
• Vinegar and lemon juice contain acids. Baking soda and milk of magnesia are bases. Water is neutral, neither an acid nor a base. From these results, can you conclude whether acids, pH neutral substances, and/or bases were able to reduce the activity of this enzyme (tyrosinase)? Can you think of a reason why some chemicals affected the enzyme while others didn't?
• Enzymes speed the rate of chemical reactions. However, the reaction may still be able to proceed without the enzyme, just more slowly. Design an experiment to determine whether or not the apples in which the enzymes have been inactivated will still turn brown within 24 hours.
• Examples of Chemical Reactions in Everyday Life
• Why Do Apple Slices Turn Brown?
• Acid-Base Chemical Reaction
• Learn the pH of Common Chemicals
• How to Make Buttermilk
• Do You Know If Milk Is an Acid or a Base?
• How to Neutralize a Base With an Acid
• How to Make Non-Toxic Glue From Milk
• How to Make a Red Cabbage pH Indicator
• Fruit Ripening and Ethylene Experiment
• Acid & Base Science Fair Project Ideas
• What Is the Acidity or pH of Milk?
• 10 Facts About Acids and Bases
• Catalysts Definition and How They Work
• How to Make a Baking Soda Volcano
• Acids and Bases Lesson Plan

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21.17: Titration Experiment

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A large amount of current research involves the development of biodiesel fuels. Often this material can be made from used vegetable oils. The vegetable oil is treated with lye to create the biofuel. In the oils is a variable amount of acid that needs to be determined, so that the workers will know how much lye to add to make the final fuel. Before the lye is added, the native vegetable oil is titrated to find out how much free acid is present. Then, the amount of lye added can be adjusted to take into account the amount needed to neutralize these free acids.

Titration Experiment

In the neutralization of hydrochloric acid by sodium hydroxide, the mole ratio of acid to base is 1:1.

\[\ce{HCl} \left( aq \right) + \ce{NaOH} \left( aq \right) \rightarrow \ce{NaCl} \left( aq \right) + \ce{H_2O} \left( l \right)\nonumber \]

One mole of \(\ce{HCl}\) would be fully neutralized by one mole of \(\ce{NaOH}\). If instead the hydrochloric acid was reacted with barium hydroxide, the mole ratio would be 2:1.

\[2 \ce{HCl} \left( aq \right) + \ce{Ba(OH)_2} \left( aq \right) \rightarrow \ce{BaCl_2} \left( aq \right) + 2 \ce{H_2O} \left( l \right)\nonumber \]

Now two moles of \(\ce{HCl}\) would be required to neutralize one mole of \(\ce{Ba(OH)_2}\). The mole ratio ensures that the number of moles of \(\ce{H^+}\) ions supplied by the acid is equal to the number of \(\ce{OH^-}\) ions supplied by the base. This must be the case for neutralization to occur. The equivalence point is the point in a neutralization reaction where the number of moles of hydrogen ions is equal to the number of moles of hydroxide ions.

In the laboratory, it is useful to have an experiment where the unknown concentration of an acid or a base can be determined. This can be accomplished by performing a controlled neutralization reaction. A titration is an experiment where a volume of a solution of known concentration is added to a volume of another solution in order to determine its concentration. Many titrations are acid-base neutralization reactions, though other types of titrations can also be performed.

In order to perform an acid-base titration, the chemist must have a way to visually detect that the neutralization reaction has occurred. An indicator is a substance that has a distinctly different color when in an acidic or basic solution. A commonly used indicator for strong acid-strong base titrations is phenolphthalein. Solutions in which a few drops of phenolphthalein have been added turn from colorless to brilliant pink as the solution turns from acidic to basic. The steps in a titration reaction are outlined below.

• A measured volume of an acid of unknown concentration is added to an Erlenmeyer flask.
• Several drops of an indicator are added to the acid and mixed by swirling the flask.
• A buret is filled with a base solution of known molarity.
• The stopcock of the buret is opened and base is slowly added to the acid, while the flask is constantly swirled to ensure mixing. The stopcock is closed at the exact point at which the indicator just changes color.

The standard solution is the solution in a titration whose concentration is known. In the titration described above, the base solution is the standard solution. It is very important in a titration to add the solution from the buret slowly, so that the point at which the indicator changes color can be found accurately. The end point of a titration is the point at which the indicator changes color. When phenolphthalein is the indicator, the end point will be signified by a faint pink color.

• The equivalence point is the point in a neutralization reaction where the number of moles of hydrogen ions is equal to the number of moles of hydroxide ions.
• A titration is an experiment where a volume of a solution of known concentration is added to a volume of another solution in order to determine its concentration. (Many titrations are acid-base neutralization reactions.)
• An indicator is a substance that has a distinctly different color when in an acidic or basic solution.
• The process for carrying out a titration is described.