Module Title: Acids and Bases in Nature and Nutrition

Abstract: Chemicals are grouped according to common properties. Acids are sour chemicals. Lemon juice or vinegar are sour because of their acid content. Bases, like baking soda, have the opposite chemical properties to acids, have no taste but tend to feel slippery. Erosion within the environment and to statues or other streetscape features can be caused by acidic ground water and rain.This module aims to communicate the theory of acids, bases and pH measurement by means of an interesting mixture of class, laboratory, home and outdoor activities. While it is important to appreciate the theoretical aspects of pH, it relates to a practical activity and students also need to appreciate by personal experience, the relevance and application of acids and bases to everyday life.

Grant Agreement number: 226646 -CP- 1- 2005-1-IE-COMENIUS-C21 (2005-3264)

Institution: Institute of Technology Tralee / Kerry Education Services

Country:Ireland

Subject: Principles and Practice of Acids, Bases and Buffers. Grade level: All Anticipated time: Variable Developer: Dr. Michael Hall

Institution Logo here

OutLab: Acids and Bases in Nature and Nutrition.Institute of Technology Tralee, IrelandTopic:Principles and Practice of Acids, Bases and Buffers.

Level of school: Primary/lower secondary/upper secondary

Duration:Primary: 1 hour in-class activity, one out-of-class activity.Lower secondary: 2 classes (theory), one practical class (e.g. 80 minutes), out-of-class project (e.g. one week duration, with report and short presentation).Upper secondary: Supplementary to above – one practical class or group project.

Required: Data logging device with pH probe, (or hand-held / portable pH meter), beakers, sample bottles (with drop strings), burette. Digital Camera.

IntroductionChemicals are grouped according to common properties. Acids are sour chemicals. Lemon juice or vinegar are sour because of their acid content. Bases, like baking soda, have the opposite chemical properties to acids, have no taste but tend to feel slippery. Erosion within the environment and to statues or other streetscape features can be caused by acidic ground water and rain.This module aims to communicate the theory of acids, bases and pH measurement by means of an interesting mixture of class, laboratory, home and outdoor activities. While it is important to appreciate the theoretical aspects of pH, it relates to a practical activity and students also need to appreciate by personal experience, the relevance and application of acids and bases to everyday life.

Pedagogical framework: The pedagogical framework of this module is built upon alternative learning environments which aim to encourage learners to integrate information instead of merely being provided with it by the teacher (Linn, Songer & Eylon, 1996). According to this view meaningful learning occurs when learners actively construct their own learning outcomes (Bruner, 1961; Mayer, 1992). More specifically, reform documents (National Science Teaching Standards, 1996) advocate the teaching and learning of science as a process of inquiry; the underlying rationale is that inquiry-based approaches have the potential to integrate the whole range of different aspects of scientific knowledge including what have been traditionally termed content and process skills.

Context:Students can find it difficult to grasp the nature of acids, bases and pH measurement. Their initial ideas about acids come from television (e.g. use of acid to dissolve prison bars) and illness (e.g. stomach pains and ulcers). The role of bases is not intuitively understood. We suggest learning is facilitated by showing the relationship between acids

and bases and their importance to society and the environment by visiting local resources and first-hand experience of acid-base chemistry.

Instructional Activities: The instructional activities focus on three main areas: preparation for the field study, the

outdoors field-study, and follow-up activities.

• Lesson 1 – Preparatory Activities in the Class Room

Duration: 80 minutes

Goal: The students construct basic knowledge about acids, bases and pH

measurement, and their relevance in nutrition and the environment.

Description of activities

TheoryAcid-base definitions and theory: Strong and weak acid and bases. The pH scale. Carbon dioxide, sulphur dioxide and the acid environment.

PracticalStudents measure the pH of milk, milk of magnesia, lemon juice, soft drinks, baking soda solution and vinegar using litmus paper, pH probe. Potential samples are listed below:

Measuring and recording pH of the following;(a) Orange and lemon juices, vinegar, milk, milk of magnesia. Antacid tablets when dissolved. Saliva, extracts of rhubarb leaves, cattle slurry. (b) Milk as it sours, or sour milk only. (c) Baking soda, washing soda (dilute solution only). (d) Toilet and drain cleaners (demonstration only).(e) Peat water, ground/cave water, pine forest drainwater, seawater, river water, tap water and distilled water.(f) Mix vinegar and baking soda solution (observe effervescence / evolution of carbon dioxide). Where possible, repeat with phenolphthalein as indicator. The solutions of baking soda and vinegar (acetic acid) are mixed and pH is measured to show neutralization reaction.

• Lesson 2 – Field study

Duration: 80 minutes

Goal: The students engage in carrying out pH measurements and observational

exercises in local amenities.

Description of activities

The teacher accompanies students to a pre-determined sampling site (e.g. river, lake,

pond, drain) and a predetermined observational walk (which could include evidence

of acid erosion, views of limestone, a visit to a cave, etc) and talk about both the

purpose of the field study but also about safety issues. The students are divided into

small groups and collect water samples at several sites using sampling vessels. They

then measure and record pH values. Students can otherwise be invited to bring water

samples from home to school for analysis. The students may also take the

temperature of the water in degrees Celsius. They perform each test twice for better

accuracy and they take notes of the results either in notebooks or on their datalogging

devices. The students may make graphical representations of the sampling site and

include their results on this diagram.

The students also visit natural interpretation centre or streetscapes to identify acid-

based erosion. Students photograph evidence of erosion and process these pictures

back at the classroom. This aspect can also form the basis of a literature (magazines,

newspapers, internet) search for similar photographs.

• Lesson 3 – Follow up activities in the classroom and at the computer lab

Duration: 80 minutes

Goals: The students engage in data interpretation and communication of their

findings.

Description of activities

The class begins with the teacher asking the students about their experiences at the

sites in terms of results collected and knowledge obtained, and the value of this

method of learning.

The students then are asked to download their data onto a computerized spreadsheet

from written notes or handhelds. They are then asked to process the data by mapping

it, constructing database tables and producing a report. Based on this analysis the

students are then asked to give a short presentation related to their work. They are

then asked to work in groups in order to prepare a powerpoint presentation to

describe the findings of their investigations.

Possible extensions

• The role of buffer solutions in the body and in biochemistry / chemistry.

• Acid-base titrations (vinegar, baking soda, burette, pH meter). Where possible,

repeat with acetate buffer and dilute hydrochloric acid). The data can be used to

construct graphs.

• Yearly variations in collected data. This data can be added to each yearly project

to provide a profile of erosion, pH, etc.

• Organization of a science fair at the school, which is open to the public and where

the students present the processes and findings of their investigation

• Write a newspaper article or similar publication (e.g. national science review

journal) based on the results obtained.

• Enter a project into the Young Scientists Competition.

Assessment

• The students are assessed through their Powerpoint presentations where they

describe the processes and findings of their investigations

• The students are also assessed for their data collection and interpretation,

participation and engagement in instructional activities and the content of their

photograph and graphical portfolios.

Additional exercises / homework

• Practical write-up using work sheets.• Write paragraphs on the formation of sketch stalactites and staligmites, include

relevant photographs; the effect of increased levels of carbon dioxide on water pH; pollutants and acid rain; acidic and basic foods.

• List experimental natural and experimental methods of trapping carbon dioxide.

Visits• Visit local cave, if possible.• Visit local bog, if possible

Resources:

School Textbook (Science)

Wikipedia.com and other internet resources (suggested search keywords: acids, bases, pH, carbon dioxide, acid rain, acid erosion, limestone, bogs).

Tourist or heritage leaflet, map of the locality

Domestic or School kitchen

Scientific Materials suppliers literature

Bibliography:

Bruner, J. (1961). The act of discovery. Harvard Educational Review, 31, 21-32.

Linn, M. C., Songer, N. B., & Eylon, B-S. (1996). Shifts and Convergences in Science

Learning and Instruction. In D. C. B. R. C. Calfee (Eds.), Handbook of

Educational Psychology (pp. 438-490). NY: Simon & Schuster Macmillan.

National Research Council (1996). National science education standards. Washington,

DC: National Academy Press

LESSON ONE WORKSHEET

Sample (name) pH pH pH Acidic / Neutral / Alkaline

Comments / Observations

The Change in pH of Milk as it becomes Sour

Type of Milk Day 1 Day Day Day Day Day

pH

pH is the measure of the acidity or basicity of a solution

It is a measure of the activity of dissolved hydrogen ions (H+)

In pure water (H2O, or H-OH) at 25°C, the concentration of H+ equals the concentration of hydroxide ions (OH-). This is defined as "neutral" and corresponds to a pH of 7.0.

ACIDS

Acids are solutions that have a pH less than 7 (i.e. more hydrogen ions than water, or more hydrogen ions than hydroxide ions).

Hydrochloric acid, sulphuric acid, nitric acid, phosphoric acid, lactic acid, acetic acid. Tartaric acid, vinegar.

BASES

Bases are solutions that have a pH greater than 7 (i.e. less hydrogen ions than water, or less hydrogen ions than hydroxide ions).

Sodium hydroxide (Caustic Soda), Potassium hydroxide, Ammonia,

Baking Soda (Sodium bicarbonate).

Molar Concentrations

Molecular Weight in g/L

NaOH (sodium hydroxide): 40

40g/L = 1 M (1mol/L)

4g/L = 0.1M

HCl (hydrochloric acid): 36

3.6g/L = 0.1M

pH = − log10[H + ]

0.1M HCl = 0.1M H+ + 0.1M Cl-

pH = - log [0.1]

pH = 1

0.01M HCl = 0.01M H+ + 0.01M Cl-

pH = - log [0.01]

pH = 2