Read the text. Which pH indicator is the most acidic? Which one is the most basic? Compare the efficient pH range of different indicator using the model.
Model:
Methyl orange ismore acidic thanlitmus.
Phenol red is less basic than alizarin yellow.
PH INDICATORS
A pH indicator is an indicator used in the titration of an acid and a base which is also called a neutralization titration. A pH indicator indicates the neutralization point or end point or equivalence point by a change in color which is distinct.
pH Indicator List
The different indicators and their efficient range of pH are given below.
| Indicator | pH range | Color acid solution | Color base solution |
| Cresol blue | 1.2 - 1.8 | Red | Yellow |
| Thymol blue | 1.2 - 2.8 | Red | Yellow |
| Methyl yellow | 2.9 - 4.0 | Red | Yellow |
| Methyl orange | 3.1 - 4.4 | Pink | Yellow |
| Methyl red | 4.2 - 6.3 | Red | Yellow |
| Litmus | 5.0 - 8.0 | Red | Blue |
| Bromothymol blue | 6.0 - 7.6 | Yellow | Blue |
| Phenol red | 6.4 - 8.2 | Yellow | Red |
| Thymol blue (base) | 8.1 - 9.6 | Yellow | Blue |
| Phenolphthalein | 8.3 - 10.0 | Colorless | Purple |
| Thymolphthalein | 8.3 - 10.5 | Colorless | Blue |
| Alizarin yellow | 10.1 - 12.0 | Blue | Yellow |
| Nitramine | 10.0 - 13.0 | Colorless | Orange/brown |
Universal pH Indicator
A universal indicator is the one which can give color changes differently at a small range of pH variations. Most common composition of a universal indicator is methanol, propan-1-ol, sodium salt of phenolphthalein, sodium salt of methyl red, bromothymol blue monosodium salt, and phenol. This is applied on strips of cellulose paper for dip test or used as aqueous solution if used in a titration. The color changes when the universal indicator is used.
| pH range | Nature | Color |
| 0 - 3 | Very acidic | Red |
| 3 - 6 | Acidic | Orange/Yellow |
| Neutral | Green | |
| 8 - 11 | Basic/base/alkali | Blue |
| 11 - 14 | Very basic/base/alkali | Purple |
Natural pH Indicator
Red cabbage juice is one of the natural indicators which can be used to detect the pH of some domestic substances. The juice can be easily extracted. The neutral solution is purple colored and when it is mixed with lemon juice it turns red indicating that the lemon solution is acidic in pH. Ammonia in small quantities is observed in adulterated milk. This can be detected with red cabbage pH indicator which turns blue in this mixture. Detergent solution which is strong in basic medium turns the red cabbage pH indicator solution in to green color.
Project Work
7. Prepare a report upon one of the following topics:
Analytical chemistry as a science.
Qualitative analysis.
Quantitative analysis.
Modern analytical chemistry.
8. Surf the Internet and prepare a report or presentation on the latest analytical chemistry news. Share the information with the groupmates.
| UNIT 4. ORGANIC CHEMISTRY |
I. Lead-in.
1. What topics does organic chemistry deal with?
2. What is the modern definition of organic chemistry?
3. What is the role of organic compounds in our life?
4. What types of organic reactions do you know?
II. Read the text and find the answers to the questions above.
TEXT A
ORGANIC CHEMISTRY
Organic chemistry is a chemistry subdiscipline involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms. Study of structure includes using spectroscopy and other physical and chemical methods to determine the chemical composition and constitution of organic compounds and materials. Study of properties includes both physical properties and chemical properties, and uses similar methods as well as methods to evaluate chemical reactivity, with the aim to understand the behavior of the organic matter in its pure form (when possible), but also in solutions, mixtures, and fabricated forms. The study of organic reactions includes both their preparation—by synthesis or by other means—as well as their subsequent reactivities, both in the laboratory and via theoretical (in silico) study.
The range of chemicals studied in organic chemistry include hydrocarbons, compounds containing only carbon and hydrogen, as well as compositions based on carbon but containing other elements. Organic chemistry overlaps with many areas including medicinal chemistry, biochemistry, organometallic chemistry, and polymer chemistry, as well as many aspects of materials science.
Organic compounds form the basis of all earthly life. They are structurally diverse. The range of application of organic compounds is enormous. They either form the basis of, or are important constituents of many products including plastics, drugs, petrochemicals, food, explosive material, and paints.
Physical properties of organic compounds typically of interest include both quantitative and qualitative features. Quantitative information includes melting point, boiling point, and index of refraction. Qualitative properties include odor, consistency, solubility, and color.
Synthetic organic chemistry is an applied science as it borders engineering, the "design, analysis, and/or construction of works for practical purposes". Organic synthesis of a novel compound is a problem solving task, where a synthesis is designed for a target molecule by selecting optimal reactions from optimal starting materials. Complex compounds can have tens of reaction steps that sequentially build the desired molecule. The synthesis proceeds by utilizing the reactivity of the functional groups in the molecule. For example, a carbonyl compound can be used as a nucleophile by converting it into an enolate, or as an electrophile; the combination of the two is called the aldol reaction. Designing practically useful syntheses always requires conducting the actual synthesis in the laboratory. The scientific practice of creating novel synthetic routes for complex molecules is called total synthesis.
Strategies to design a synthesis include retrosynthesis, popularized by E. J. Corey, starts with the target molecule and splices it to pieces according to known reactions. The pieces, or the proposed precursors, receive the same treatment, until available and ideally inexpensive starting materials are reached. Then, the retrosynthesis is written in the opposite direction to give the synthesis. A "synthetic tree" can be constructed, because each compound and also each precursor has multiple syntheses.
Organic reactions are chemical reactions involving organic compounds. Many of these reactions are associated with functional groups. The general theory of these reactions involves careful analysis of such properties as the electron affinity of key atoms, bond strengths and steric hindrance. These factors can determine the relative stability of short-lived reactive intermediates, which usually directly determine the path of the reaction.
The basic reaction types are: addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and redox reactions. An example of a common reaction is a substitution reaction written as:
Nu− + C-X → C-Nu + X− ,where X is some functional group and Nu is a nucleophile.
The number of possible organic reactions is basically infinite. However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens in sequence—although the detailed description of steps is not always clear from a list of reactants alone.
The stepwise course of any given reaction mechanism can be represented using arrow pushing techniques in which curved arrows are used to track the movement of electrons as starting materials transition through intermediates to final products.
Tasks