Unit 4 Acids and Bases

Unit 4

Acids and Bases

Table of Contents Introduction 3

Essential Questions 4

Review 4

Lesson 4.1: Identifying Acids and Bases 5

Objectives Warm-up Learn about It Key Points Web Links Check Your Understanding Challenge Yourself

5 5 6

10 10 11 12

Lesson 4.2: Strengths of Acids and Bases 13

Objectives Warm-up Learn about It Key Points Web Links Check Your Understanding Challenge Yourself

13 13 14 20 21 22 23

Lesson 4.3: Safety Precautions in Handling Acids and Bases 24

Objective Warm-up Learn about It Key Points Web Links Check Your Understanding Challenge Yourself

24 24 25 28 29 29 30

Laboratory Activity 31

Performance Task 34

Self Check 36

Key Words 36

Wrap up 38

Photo Credits 38

References 38

Copyright © 2018 Quipper Limited 2

Acids and bases play a big part in chemistry because a lot of reactions can be classified as acid-base reactions. Acid-base reactions do not only happen in the laboratory. Many bodily functions are also governed by acids and bases. For example, our stomach contains a mixture of very powerful acids that can digest a variety of food. Our blood is slightly basic to accommodate acids released during energy production. Most acid-base reactions are also naturally occurring. More so, most of the things you see in nature and those that are commonly used as household substances can be classified as either acids or bases. Oranges and other citrus fruits are acidic. They taste sour like vinegar. Corals are made up of a basic compound known as calcium carbonate. Soaps, detergents and other cleaning agents are similarly classified as bases. But what exactly are acids and bases? In this unit, you will learn about acids and bases. You will be able to classify substances as acids and bases and recognize their general properties.


At the end of this unit, you should be able to answer the following questions.

● What are acids and bases? ● What are the general properties of acids and bases? ● What is pH? How can one classify substances based on their pH? ● What are the proper ways to handle acids and bases?

● A solution is a homogeneous mixture made up of two or more pure substances physically combined. It is made up of a solute dissolved in a solvent. Particles of a solution are invisible to the naked eye.

● A pure substance is a type of matter with a definite composition. It is simply called substance.

● Dissociation is a chemical process wherein a molecule breaks down forming its constituent ions. This process is a reversible reaction.


While cleaning the bath room, large amount of liquid sosa was spilled to your skin. Your mom instructed you to pour vinegar on your skin to neutralize the burn as a first aid. Liquid sosa or sodium hydroxide is a base while vinegar is an acid. What are acids and bases? How are they different from one another?

A or B? Form a group of five and do the following mini-experiment. Follow the steps carefully and observe what is being asked. Materials:

● vinegar, 10 mL ● liquid sosa, 10 mL ● beaker or plastic containers

Procedure:

1. Pour the vinegar and liquid sosa in separate beakers or containers. Observe their physical properties. Record their color, appearance and smell below.

2. Mix the two substances to form a new solution. Then, record your observations in terms of color, appearance and smell in the same table below.

3. Be ready to report your observations to the class.


Data and Results:

Properties Vinegar Liquid Sosa New Solution

Color

Appearance

Smell

Guide Questions:

1. What are the similarities and the differences in the color, appearance, and smell of the vinegar, liquid sosa, and the new solution?

2. What is the possible identity of the new solution?

Properties of Acids and Bases Acids and bases are made up of two or more elements combined chemically. Hence, acids and bases are also compounds. The properties of acids and bases are summarized in the table below.

Table 4.1. Characteristics of Acids and Bases. Acids Bases

Sour taste Bitter taste

Hot and corrosive Slippery texture

Irritating smell Irritating smell

Good conductors of electricity Good conductors of electricity

Reacts with metals to produce hydrogen gas Reacts with fats to form soap A litmus paper test is a rapid and the most common test used to determine if a given solution is acidic or basic. The litmus paper contains water soluble dyes from lichens absorbed in a filter paper. It has two types: the red litmus paper and the blue litmus paper. An acid turns the color of blue litmus paper to red. A base turns the color of red litmus paper to blue.


Fig. 1. Strips of blue and red litmus paper.

When an acid reacts with a base, water and salt is formed. The reaction is called neutralization. A salt is a compound formed by reacting an acid and a base.

acid + base → salt + water

For example, the reaction of muriatic acid (HCl) with lye water (NaOH) produces salt (NaCl) and water (H2O), as shown below.

HCl + NaOH → NaCl + H2O You may not notice it but acids and bases are part of many commonly used household and industrial compounds. Fruit juices are acids or may contain acids. Cleaning agents like soap are bases. Compounds that could act as an acid or a base are called amphoteric compounds. Water is an example of an amphoteric compound. Arrhenius Theory To further describe acids and bases, several scientists have proposed theories to explain the concepts of acids and bases. One of this theory is the Arrhenius Theory by Svante Arrhenius. He recognized the nature of acids and bases through his experiments on electrolytes.


In his theory, an Arrhenius acid is a substance that dissociates in water to form hydrogen ions (H+). The hydrogen ion protonates the water to yield the hydronium ion (H3O+). An Arrhenius acid increases the concentration of hydronium ion in an aqueous solution.

Fig. 2. When an acid dissociates in water, it forms hydrogen ions.

For example, hydrochloric acid (HCl) dissociates in water to form H+ and Cl- ions. Hence, hydrochloric acid is an Arrhenius acid. An Arrhenius base is a substance that dissociates in water to form hydroxide ions (OH-). A base increases the concentration of OH- ions in an aqueous solution.

Fig. 3. When a base dissociates in water, it forms hydroxide ions.

Sodium hydroxide (NaOH) dissociates in water to form Na+ and OH- ions. Hence, sodium hydroxide is an Arrhenius base.


The definition of Arrhenius acids and bases are limited to aqueous solutions. Arrhenius theory also limits the type of bases to substances with hydroxides. There are other theories, which is not the scope of this grade level, that discusses other definitions of acids and bases. Other example of common household Arrhenius acids and Arrhenius bases are illustrated below. Vinegar, vitamin C, muriatic acid and battery acid are classified as acids, while drain cleaner and antacids are classified as bases.

Fig. 4. Some household examples of Arrhenius acids and Arrhenius bases.


● Acids and bases are made up of two or more elements combined chemically. ○ Acids have a sour taste, irritating smell, and hot and corrosive. It is

also a good conductor of electricity. It reacts with metals to produce hydrogen gas.

○ Bases have a bitter taste, irritating smell, and slipper texture. It is also a good conductor of electricity. It reacts with fats to form soap.

● A litmus paper test is a rapid and the most common test used to determine if a given solution is acidic or basic.

○ An acid turns the color of blue litmus paper to red. ○ A base turns the color of red litmus paper to blue.

● When an acid reacts with a bases, water and salt is formed. The reaction is called a neutralization reaction.

● Compounds that could act as an acid or a base are called amphoteric compounds.

● The Arrhenius theory by Svante Arrhenius explains the concept of acids and bases based on the dissociation in water.

○ An Arrhenius acid is a substance that dissociates in water to form hydrogen ions (H+).

○ An Arrhenius base is a substance that dissociates in water to form hydroxide ions (OH-).

Let us visit the following sites to learn more about this lesson.

● Make your own version of the litmus paper! Follow the steps here: Alpha Studios. 2015. ‘Make Your Own Litmus Paper at Home.’

https://www.youtube.com/watch?v=pL-xdGjJ7Lg

● Who is Svante Arrhenius? Read the complete life and works of a Nobel Prize Winner: Crawford, Elisabeth. 2018. ‘Svante Arrhenius.’ https://www.britannica.com/biography/Svante-Arrhenius




https://www.britannica.com/biography/Svante-Arrhenius

https://www.britannica.com/biography/Svante-Arrhenius

A. Write A if the property described below is for acids. Otherwise, write B is the

property described is for bases. If the given property is exhibited by both acids and bases, write C.

1. sour taste 2. slippery texture 3. reacts with metal to form hydrogen gas 4. turns blue litmus paper to red 5. produces H+ in water 6. bitter taste 7. irritating smell 8. reacts with metal to form metal hydroxides 9. turns red litmus paper to blue

10. good conductors of electricity B. Identify if the following compound is an acid or a base.

1. vinegar, containing acetic acid 2. liquid sosa, containing sodium hydroxide 3. milk of magnesia, containing magnesium hydroxide 4. soft drinks, containing carbonic acid 5. potassium hydroxide 6. tea 7. orange juice 8. bitter gourd 9. coffee drink

10. rain water


Answer the following problems comprehensively.

1. You have an unknown substance X. You want to test whether it is an acid or a base. Unfortunately, you only have red litmus papers. You dip the litmus paper in the solution and nothing happened. Is substance X acidic or basic? Or neither? Why?

2. You have learned that an acid and a base reacts in a neutralization reaction to form a salt and a water molecule. Write an equation representing the reaction of nitric acid, HNO3, and potassium hydroxide, KOH.

3. Provide at least two more examples of an amphoteric substance. 4. No amphoteric substances actually exist as 100 percent pure. Suggest a

possible reason for this. 5. What are the limitations of Arrhenius theory?


When your mom cooks your favorite adobo, she uses vinegar. The sour taste of vinegar is due to acetic acid which is only present in less than 5%. Have you ever wondered why vinegar is only 5% acid? Another acid, muriatic acid is too strong that it could cause skin burns. What are strong acids and bases? How do they differ from weak acids and bases?

A or B (Part II) Form a group of five and do the following mini-experiment. Follow the steps carefully and observe what is being asked. Materials:

● solution A (liquid sosa) ● solution B (clear ammonia solution) ● solution C (muriatic acid) ● solution D (vinegar) ● clear plastic containers ● 9 volts battery power pack ● bulb holder ● 3 volts bulb flashlight ● insulated wire, 22 gauge


Procedure: 1. Secure a small amount of solutions A, B, C, and D in separate clear, plastic

containers. 2. Observe their color, appearance and smell. Record these properties on the

table below. Can you tell whether they are acidic or basic? Record also your findings below.

3. Improvise a simple conductivity tester. Connect the positive end of the power pack to the bulb fixed by the bulb holder using insulated wires. Connect also another piece of wire in the negative end of the power pack. Expose the two ends acting as the “testers” by peeling off a bit of the insulating materials.

4. Test the conductivity of each solution. Carefully observe the intensity of the light bulb, it it lights. Record your same observation on the table below.

Data and Results:

Samples Color Appearance Smell Conductivity Acidic or basic?

A

B

C

D

Strong and Weak Acids Acids can be classified as either a strong acid or a weak acid. The basis for classification is the ability of the acid to dissociate in water. A strong acid completely dissociates in water to yield hydrogen (H+) ions. A weak acid does not dissociate completely in water. The amount of dissociation for weak acids is usually less than 1%. There are only six strong acids in aqueous solution. These are:

1. hydrochloric acid, HCl 2. hydrobromic acid, HBr 3. hydroiodic acid, HI


4. nitric acid, HNO3 5. perchloric acid, HClO4 6. sulfuric acid, H2SO4 (for the first dissociation of hydrogen ion only)

Fig. 5. Examples of strong acids and weak acids.

Strong acids are caustic or corrosive to surfaces. They are best used as cleaning agents in surfaces such as metallic sinks and ceramic tiles. For example, muriatic acid is a solution of hydrochloric acid. It is a strong acid used in industrial plants as an iron cleaner. It is the same acid found in the stomach because it aids in digestion and absorption of food. Weak acids are not as caustic as strong acids. In fact, some of them can be found in food such as acetic acid in vinegar and ascorbic acid in citrus fruits.

Strong and Weak Bases Like acids, there are also strong and weak bases. A strong base completely dissociates in water to yield hydroxide (OH-) ions. A weak base does not dissociate completely in water.


Hydroxides of alkali metals (Group 1 elements) and alkaline earth metals (Group 2 elements) are strong bases. Some examples of strong bases are are:

1. sodium hydroxide, NaOH 2. potassium hydroxide, KOH 3. magnesium hydroxide, Mg(OH)2 4. calcium hydroxide, Ca(OH)2

Fig. 6. An example of a strong base and a weak base.

Strong bases are also caustic and are skin irritants. They are often used as cleaners and neutralizers. For example, sodium hydroxide is a strong base used in drain and oven cleaners. Another strong base, calcium hydroxide or lime, is used to neutralize acidic soils. Weak bases are not as caustic as strong bases. Ammonia is an example of a weak base. It is also used as a cleaner and an ingredient for making fertilizers. The pH scale The acidity or basicity of a solution depends on the concentration of hydronium ions (H3O+) and hydroxide ions (OH-) dissolved in a solution. The pH scale is a simple numerical way of describing the acidity of a solution. It was proposed by Danish chemist Søren Peder Lauritz Sørensen.


Values of pH ranges from 1 to 14. Each region of the pH scale maybe used to identify an acidic, basic, or neutral solution. pH values between 1 to 7 are acidic while pH values between 7 to 14 are basic. A pH value of 7 means that the solution is neutral.

Fig. 7. The pH scale

The pH values of certain commons chemicals at home are shown below.

Fig. 8. pH values of common household products.


Acid-Base Indicators To determine whether a compound is an acid or a base, acid-base indicators are used. An acid-base indicator is a substance that changes into a specific color for certain pH ranges, usually one range for acids and another for bases. An acidic solution corresponds to a specific color while a basic solution corresponds to another specific color. An acid-base indicator could be obtained naturally from plants or chemically prepared pH indicators. There are certain plants that are used to act as an acid-base indicator. These are called natural indicators. Below is a list of common natural indicators and the specific color for acids and bases. Eggplant peel is usually used as a natural acid-base indicator.

Fig. 9. Colors of solutions at different pH levels using red cabbage as indicator.


Since it is tedious to prepare natural indicators, there are readily available indicators that could be used for specific pH ranges. These are called pH indicators. The active compound in pH indicators also shows a specific color for acidic and basic solutions. Below is a list of common pH indicators and the specific color for acids and bases. Phenolphthalein is the most common pH indicator.

Fig. 10. Colors of solutions at different pH levels using phenolphthalein as indicator. Measurement of pH An improved version of the litmus paper is the pH paper. The pH paper can determine the approximate pH value of a certain solution from pH 1 to 14. It contains a mixture of pH indicators called the universal indicator that can determine the specific pH range of the solution. The color is matched to the given color chart.


Fig. 11. pH paper.

An analytical tool called the pH meter is used to quantitatively determine the exact pH of the solution.

Fig. 12. pH meter.

● A strong acid completely dissociates in water to yield hydrogen (H+) ions. A weak acid does not dissociate completely in water.

● A strong base completely dissociates in water to yield hydroxide (OH-) ions. A weak base does not dissociate completely in water.

● The pH scale is a simple numerical way of describing the acidity of a solution. ○ pH values between 1 to 7 are acidic.


○ pH value of 7 means that the solution is neutral. ○ pH values between 7 to 14 are basic.

● An acid-base indicator is a substance that changes into a specific color for certain pH ranges, usually one range for acids and another for bases.

● Plants that are used as acid-base indicators are called natural indicators. ● pH indicators are readily available indicators that could be used for specific

pH ranges. ● pH paper is used to determine the approximate pH value of a certain

solution from pH 1 to 14. It contains a mixture of pH indicators called the universal indicator.

● The pH meter is used to quantitatively determine the exact pH of the solution.

Let us visit the following sites to learn more about this lesson.

● How to use a pH meter? Watch this video to know how pH of solutions are measured with a pH meter: Bio-Rad Laboratories. 2012. ‘Using a pH Meter.’ https://www.youtube.com/watch?v=vwY-xWMam7o

● How are pH papers made? These precision papers contain colors extracted and fused with glossy paper: Precision Laboratories, Inc. 2015. ‘How Its Made: Paper Test Strips.’ https://www.youtube.com/watch?v=hjEkAxPiua8&t=13s

● Read about the famous scientist who made our life easier in terms of measuring acid and base strengths: Science History Institute. 2018. ‘Søren Sørensen.’ https://www.sciencehistory.org/historical-profile/soren-sorensen


https://www.youtube.com/watch?v=vwY-xWMam7o

https://www.youtube.com/watch?v=vwY-xWMam7o

https://www.youtube.com/watch?v=hjEkAxPiua8&t=13s

https://www.youtube.com/watch?v=hjEkAxPiua8&t=13s

https://www.sciencehistory.org/historical-profile/soren-sorensen

https://www.sciencehistory.org/historical-profile/soren-sorensen

A. Classify the following as either as a strong acid, weak acid, strong base, or weak

base. 1. hydrofluoric acid, HF 2. ammonia, NH3 3. potassium hydroxide, KOH 4. sulfuric acid, H2SO4 5. barium hydroxide, Ba(OH)2 6. acetic acid, CH3COOH 7. hydroiodic acid, HI 8. perchloric acid, HClO4

9. aluminum hydroxide, Al(OH)3 10. hypoiodous acid, HIO

B. Assess the following statements if its true or false. Write T if the statement is

true. Otherwise, write F. 1. HI, HBr, HCl, and HF are all strong acids. 2. H2SO4 is a strong acid even up to its second ionizable hydrogen ion. 3. NaOH and KOH are examples of strong bases. 4. A solution with a pH value of 6 is considered to be slightly basic. 5. Plants that are used as acid-base indicators are called natural indicators. 6. A litmus paper can tell you the pH of a solution. 7. A solution that turns red cabbage red is most likely acidic. 8. A solution that turns phenolphthalein colorless is most likely basic. 9. The pH paper can measure pH values from 1 to 14.

10. The exact pH of a solution, even at two decimal places, can be given to you by a litmus paper.


Answer the following problems comprehensively.

1. Suppose there are two beakers, one containing a fixed number of molecules of hydrochloric acid and the other one containing the same number of molecules of acetic acid. Will the solutions have the same pH values? Explain your answer.

2. From the same given situation in the previous item, which do you think will light up a bulb in a conductivity set-up brighter?

3. Do acid strength and pH correlate? In simpler terms, are strong acids always have low pH values (like around 1 to 2) and cannot have relatively higher pH values (around 5 to 6)? Explain your answer.

4. If water is neutral, what does this suggest to its pH value? Can you think of other substances that are neutral?

5. Explain why it is impossible to have pH values less than zero and above fourteen.


Some acids and bases are corrosive. When spilled on your skin, it might cause skin burn. Most acids and bases are also irritant. Strong acids even produce fumes that are very toxic to lungs when inhaled. Strong bases are very corrosive, too. It is therefore of utmost importance to handle these substances with extensive care. What will you do in case a sample of a strong acid gets spilled?

Strong or Weak? Form a group of five and do the following mini-experiment. Follow the steps carefully and observe what is being asked. Materials:

● solution A, liquid sosa ● solution B, washing soda solution (dissolve 1 g in 10 mL water) ● solution C, muriatic acid ● solution D, carbonated drink ● small beakers or containers ● improvised conductivity set-up

Procedure:

1. Secure a small amount of solutions A, B, C, and D in separate clear, plastic containers.

2. Improvise a simple conductivity tester. Connect the positive end of the power pack to the bulb fixed by the bulb holder using insulated wires. Connect also another piece of wire in the negative end of the power pack. Expose the two


ends acting as the “testers” by peeling off a bit of the insulating materials. 3. Test the conductivity of each solution. Carefully observe the intensity of the

light bulb, it it lights. Record your same observation on the table below. 4. For each solution, try to move the testers wider apart. Observe if there are

fluctuations in the intensity of the light bulb. Record further observations below.

Data and Results:

Sample Initial intensity of the light bulb

Observations on the intensity of the light bulb when the testers are moved

wider apart

A

B

C

D

Handling Acids and Bases There will always be risks involved when working with chemicals in a laboratory. Even working with water can be quite dangerous! You should always know what to do to before, during, and after a laboratory experiment. Personal Protective Equipment You should always wear personal protective equipment when in the laboratory. This includes a lab coat, eye goggles, comfortable clothing, closed shoes, long pants, and gloves. Lab coats provide general protection for your clothing and skin. Acids and bases can easily damage eye tissue. Wearing protective goggles is a must. Closed shoes are recommended to protect our feet from unforeseen spills. Gloves must be used especially when handling acids and bases. The general idea is that there should be least exposed skin as possible.


Fig. 13. A complete personal protective equipment in the laboratory.

Material Safety Data Sheets When working with chemicals, it is best to check the material safety data sheet (MSDS) to look for information about the substances that you will handle. It is very important to know the general hazards involved with the chemicals you are about to handle. Find out if the particular acid or base you are working on is corrosive, or even toxic. MSDS will also give out information regarding health effects of the compound you are working on. There are a lot of MSDS databases online that you can consult. General Health Effects Generally, acids and bases are irritants. Concentrated acids and bases can easily damage tissue. Contact can cause severe damage to skin and eyes. Concentrated gases can also damage skin, eyes, and lungs. Inhaling even dry powders can cause severe respiratory damage.


Fig. 14. An example of a Material Safety Data Sheet (MSDS).

Working with Acids and Bases Some of the most common compounds you will use in the lab are acids and bases. Work with acids and bases in well-ventilated rooms. Work with small amounts. Do not mix acids and bases unless it is what is required in your experiment. Neutralization reactions can release a lot of heat and may cause damage. Never add water to acids or bases. Dilute acids and bases by adding them in water and not the other way around. Water can act as an acid or a base. Adding water to


concentrated acids and bases can release heat that can cause an explosion. Adding acids or bases to a larger volume of water dissipates the heat of the reaction safely. In Case of Spills Spills should be neutralized immediately and cleaned up using a paper towel or a sponge. For acid spills, do not use a strong base to avoid violent reactions. Sodium carbonate is best used to avoid chances of injury. Base spills should be neutralized using boric acid. Acetic acid, though a weak acid could still react strongly with a base. For cases of spills on the skin, do not neutralize. Wash well with running water. Neutralizing a spill on the skin can lead to a worse injury. Waste Procedures Every laboratory must have protocols on how to dispose of chemical wastes. Some low concentration acids and bases may be diluted and flushed down the sink. However, most chemical wastes must be collected on a chemical waste jar and disposed of according to the laboratory standard operating procedures.

● Always wear personal protective equipment when in the laboratory. This includes a lab coat, eye goggles, comfortable clothing, closed shoes, long pants, and gloves.

● When working with chemicals, it is best to check the material safety data sheet (MSDS).

● Generally, acids and bases are irritants. ● Work with small amounts of acids and bases. Never add water to acids or

bases.


● Spills should be neutralized immediately and cleaned up using a paper towel or a sponge. For cases of spills on the skin, do not neutralize. Wash well with running water.

● Dispose chemical wastes properly.

For further information, you can check the following web links:

● What happens when you (intentionally) add water to acid? But kids, this is just a proof of concept! Do not try this at home: Cody’sLab. 2014. ’Adding Water to Acid; Finally a Reaction!’ https://www.youtube.com/watch?v=_f0vK8Wffgg

● Be careful of these acids - these are the strongest among the strongest: SciShow. 2016. ‘The Strongest Acids in the World.’ https://www.youtube.com/watch?v=cbN37yRV-ZY

A. Read the following passage and identify which of the following laboratory

techniques or incidences are wrong.

Charlene is running late for her Chemistry laboratory class. The strap of her slippers almost tore apart as she rushed to her classroom. She put on her lab coat and immediately goes through her class experiment. She adds water to the flask with acid to dilute the acid into half its concentration. She directly smells one of the flasks to find out which one is the base. To make sure, she uses a spatula to scoop some of the acid to her hand so she could feel if it is indeed slippery. She adds the acid and the base as indicated in her lab manual. The swirls the flask vigorously. She didn’t notice the heat from the flask until the flask breaks and she


https://www.youtube.com/watch?v=_f0vK8Wffgg

https://www.youtube.com/watch?v=_f0vK8Wffgg

https://www.youtube.com/watch?v=cbN37yRV-ZY

https://www.youtube.com/watch?v=cbN37yRV-ZY

spills the contents onto the table. She immediately runs to her teacher to tell her what happened. She then struts to the comfort room to wash her hands that got wet with the spill.

B. Assess the following statements if its true or false. Write T if the statement is

true. Otherwise, write F. 1. Lab coats provide general protection for your clothing and skin. 2. Gloves must be used especially when handling acids and bases. 3. When working with chemicals, it is best to check the material safety data

sheet (MSDS) to look for information about the substances that you will handle.

4. Inhaling dry powders can cause severe respiratory damage. 5. Dilute acids and bases by adding water into them in a volumetric flask. 6. For cases of spills on the skin, do not neutralize. 7. Some low concentration acids and bases may be diluted and flushed down

the sink. 8. Concentrated acids and bases are noncorrosive and not irritant. 9. Closed shoes are recommended to protect our hands from unforeseen

spills. 10. We can touch acids and bases directly to exactly feel the temperature by

hand.

Answer the following questions comprehensively.

1. Should weak acids or bases be treated lightly compared to strong acids or bases?

2. Why should water be never added to concentrated acids? 3. What should you do if you accidentally spill a base of unknown concentration

on your shirt? 4. Should all spills be neutralized? 5. Why is it not advisable to neutralize spills with concentrated acids/bases?


Activity 4.1 Testing the Acidity and Basicity of Household Compounds

Objectives At the end of this laboratory activity, the students should be able to:

● produce a natural acid-base indicator from red cabbage; and ● test the acidity and basicity of household compounds using the previously

prepared natural indicator. Materials and Equipment

● red cabbage ● muriatic acid ● liquid sosa ● vinegar ● tea ● tomato juice ● orange juice ● ammonia ● detergent

● milk ● baking soda ● bleach ● distilled water ● tap water ● beakers or containers ● test tubes ● hot plate ● balance

Procedure Preparing a Natural Indicator from Red Cabbage

1. Weigh 50 g of red cabbage. Cut it into small pieces and wash thoroughly. 2. Put the sliced red cabbage in a 500 mL beaker. Fill the beaker with enough

distilled water until it’s three-fourths full. 3. Heat the beaker at 1000C for 20 minutes. Observe for the appearance of

color. Record your observation on the table below. 4. Cool the solution by passing running water outside the walls of the beaker.

Carefully decant the colored solution in another container, preventing the leaves from being transferred. Keep the obtained solution for the next parts of the experiment.


Identifying the Color of the Natural Indicator at Different pHs 1. Prepare two sets of test tubes and label them A and B. 2. Transfer enough solution of the natural indicator you previously prepared

until the test tube is three-fourths filled. 3. To the test tube labelled A, add 5 drops of muriatic acid. Observe any

changes in color. Then, continue adding muriatic acid drop by drop and stop whenever there is a color change. Mix the test tube by rolling it with the palm of your hands. Record the observed color of the natural indicator and the number of drops it took you to reach that color. Stop adding when you reached the color red.

4. Do the same for test tube labelled B, but add liquid sosa instead of muriatic acid. Record the observed color of the natural indicator and the number of drops it took you to reach that color. Stop adding when you reached the color yellow.

Identifying the Acidity and Basicity of Household Compounds

1. There are eleven solutions that will be tested against the natural indicator: vinegar, tea, tomato juice, orange juice, ammonia, detergent, milk, baking soda, bleach, distilled water and tap water.

2. Prepare the natural indicator solution in eleven separate solutions. Transfer enough solution to fill half of the test tube.

3. Label each test tube with the test solutions. Accordingly, transfer enough test solutions to each respective test tubes containing the natural indicator until the test tube is three-fourths filled.

4. Observe the colors of each solution. Record your observations on the table below.

Waste Disposal Dispose all solids in the trash can. All solutions can be disposed in the sink with excess amount of running water.


Data and Results Record your observations on the table below.

Table 1. Observations on the natural indicator from red cabbage.

Test tube A Test tube B

No. of drops added

Color observed No. of drops added

Color observed

0 0

Table 2. Acidity and basicity of household compounds

Household compound

Color of the natural indicator Acidic or basic Estimated pH

vinegar

tea

tomato juice

orange juice

ammonia

detergent

milk

baking soda

bleach

distilled water

tap water


Guide Questions

1. What is the original color of the natural indicator extracted from red cabbage?

2. Do you think we can also extract natural indicators from other colored leaves, such as onion and eggplant?

3. Research on the identity of the substance present in red cabbage that acts as the natural indicator. What is its chemical identity?

4. Assess whether the household materials are acidic or basic, depending on the resulting color of the natural indicator.

5. Estimate the pH of each solution using the data in Table 2. Relatively assign pH values based on the number of drops of muriatic acid or liquid sosa added and their color. Correlate this data to estimate the pH of each household materials.

6. From your data, which is more acidic, a tomato juice or an orange juice? Which is more basic, baking soda or bleach? Is tap water acidic or basic?

Producing Acid-Base Indicators from Plants Plants and fungi that are usually colored contains a class of compounds known as anthocyanins. These compounds change colors based on the acidity or basicity of their environment. The pH paper is made up of dried anthocyanins from lichens pressed in a paper. Their color changes with pH, with the color change distinct enough to differentiate by at least 1 pH unit. Some plants have been actually used in ancient times as natural pH indicators, either of soil or of rainwater. Goal

● Your task is to produce your own acid-base indicator from a naturally occurring plant.

● The problem/challenge is how will you be able to extract a natural indicator from the plant of your choice.

Role

● You are a part of a group of brilliant student scientists who study General Chemistry.


Audience

● Your audience is your class. Situation

● Search for locally available plants that contain anthocyanins. This will be your source of the natural indicator.

Product, Performance, and Purpose To be able to achieve your purpose, follow these steps:

● Cut small pieces of the leaves and boil it in water until the color appeared. ● Prepare set-ups of varying pH values by adding varying amounts of muriatic

acid and liquid sosa. ● Observe the colors and tabulate your result. ● You can directly measure the pH of each solutions using a pH paper or a pH

meter. However, if there are no available means of doing this, you can estimate the pH by correlating the color of each solution and the amount of liquid sosa or muriatic acid being added. You can also search the literature if there are available data for the anthocyanin present in your chosen plant.

● Report your findings in the class. Standards and Criteria for Success:

● Your work must meet the standards found in the rubric below.

Criteria Below

Expectations 0% to 49%

Needs Improvement

50% to 74%

Successful Performance

75 to 99%

Exemplary Performance

100%

Research and Analysis of Literature, Organization

Report shows no organization

Shows some organization, but report did not flow smoothly from one idea to the other

Organized, but lacks few details needed to completely explain the topic

Very organized and comprehensive, report carefully planned out and has met the objectives

Correctness of data

No data presented

Shows some data, but most are incorrectly inferred

Shows all data but contains minor errors in data analysis and inference

Shows all data that meet the objectives of the experiment

Communication skills

Was not able to communicate his thoughts

Was able to communicate some thoughts

Was able to communicate, but some are not well explained

Was able to communicate, presented the report in a manner well understood by the audience


After studying this unit, can you now do the following?

Check I can…

recognize acids and bases.

differentiate strong acids and bases from weak acids and bases.

enumerate proper precautions in handling acids and bases.

Acids These compounds have a sour taste, irritating smell, and are usually hot and corrosive. They are good conductors of electricity and react with metals to produce hydrogen gas.

Acid-base indicator An acid-base indicator is a substance that changes into a specific color for certain pH ranges, usually one range for acids and another for bases.

Amphoteric compounds

These compounds can act either as an acid or a base.

Arrhenius acid An Arrhenius acid is a substance that dissociates in water to form hydrogen ions (H+).

Arrhenius base An Arrhenius base is a substance that dissociates in water to form hydroxide ions (OH-).

Bases These compounds have a bitter taste, irritating smell, and slipper texture. They are also good conductors of electricity and reacts with fats to form soap.


Litmus paper test It is a rapid and the most common test used to determine if a given solution is acidic or basic. An acid turns the color of blue litmus paper to red. A base turns the color of red litmus paper to blue.

Material Safety Data Sheet (MSDS)

It contains a lot of information on various chemicals including physical and chemical properties, toxicity and hazard, and first aids.

Natural indicator These are acid-base indicators obtained from plants.

Neutralization reaction

It is the reaction of an acid and a base.

Personal protective equipment

A complete personal protective equipment includes a lab coat, eye goggles, comfortable clothing, closed shoes, long pants, and gloves.

pH indicators pH indicators are readily available indicators that could be used for specific pH ranges.

pH meter The pH meter is used to quantitatively determine the exact pH of the solution.

pH paper pH paper is used to determine the approximate pH value of a certain solution from pH 1 to 14. It contains a mixture of pH indicators called the universal indicator.

pH scale The pH scale is a simple numerical way of describing the acidity of a solution. pH values between 1 to 7 are acidic. pH value of 7 means that the solution is neutral. pH values between 7 to 14 are basic.

Strong acid A strong acid completely dissociates in water to yield hydrogen (H+) ions.

Strong base A strong base completely dissociates in water to yield hydroxide (OH-) ions.

Weak acid A weak acid is an acid that does not dissociate completely in water.

Weak base A weak base is a base does not dissociate completely in water.


Acids and Bases

Fig. 1. Blue and Red litmus papers by Kanesskong is licensed under CC BY-SA 4.0 via Wikimedia Commons. Fig. 12. pH meter togopic by Togopic is licensed under CC BY-SA 3.0 via Wikimedia Commons.

Mendoza, E. 2003. Chemistry. Quezon City: Phoenix Publishing House, Inc. Padolina, M.C.D., Simon-Antero, E. and Alumaga, M.J.B. 2010. Conceptual and

Functional Chemistry (2nd ed.). Quezon City: Vibal Publishing House, Inc.


https://commons.wikimedia.org/wiki/File:Blue_and_Red_litmus_papers.jpg

https://commons.wikimedia.org/wiki/User:Kanesskong

https://creativecommons.org/licenses/by-sa/4.0/legalcode

http://commons.wikimedia.org/

https://commons.wikimedia.org/wiki/File:PH_meter_togopic.png

https://commons.wikimedia.org/w/index.php?title=User:Togopic&action=edit&redlink=1

https://creativecommons.org/licenses/by/3.0/deed.en



Religioso, T.F. and Vengco, L.G. 2011. You and the Natural World Integrated Science (3rd ed.). Quezon City: Phoenix Publishing House, Inc.

Northwestern University. “Laboratory Safety.” Accessed April 9, 2017.

http://faculty.washington.edu/korshin/Class-486/AEESP-safety-notes.pdf Purdue University. “The Lewis definitions of acids and bases.” Accessed April 8,

2017. http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch11/lewis.php

Wisonsin University. “ChemPages Netorials – Acids and Bases Module.:”Accessed

April 7, 2017. https://www.chem.wisc.edu/deptfiles/genchem/netorial/rottosen/tutorial/modules/acid_base/index.htm


http://faculty.washington.edu/korshin/Class-486/AEESP-safety-notes.pdf

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch11/lewis.php

https://www.chem.wisc.edu/deptfiles/genchem/netorial/rottosen/tutorial/modules/acid_base/index.htm

https://www.chem.wisc.edu/deptfiles/genchem/netorial/rottosen/tutorial/modules/acid_base/index.htm

Documents

Unit 4 Acids and Bases