Maharashtra Board Class 11 Chemistry Chapter 16 Chemistry in Everyday Life PDF Download

Chemistry In Everyday Life

The life, the atmosphere, the earth and the universe, all have evolved over billions of years to the present state. The evolution continues progress and accompanied by a variety of chemical changes. Natural phenomena such as weathering, lightening, irruption of volcanoes, photosynthesis, ripening of fruit, fermentation, release of fragrance by blooming flowers and many others take around us involve intricate chemistry. Chemistry is involved in a variety of life processes those occur within and across our body. Human civilization in different regions of the world discovered uses of various plant, animal and mineral products for benefits of human life. With the advent of modern science, scientist discovered structures of various constituent chemicals in natural materials. Synthetic organic chemistry has led to advancement in science. Synthesis of natural molecules and new molecules with structural variation revolutionalized materials are used in all the walks of human life. This influence is seen in all aspects of the basic needs, such as food, clothing, shelter and beyond.

In this chapter, we consider some aspects of food chemistry, medicinal chemistry and chemistry of cleansing materials with reference to compounds having simple structural features.

Can You Recall?

1. What are the components of balanced diet?

2. Why is food cooked? What is the difference in the physical states of uncooked and cooked food?

3. What are the chemicals that we come across in everyday life?

Just Think

1. Why is food stored for a long time?

2. What methods are used for preservation of food?

3. What is meant by quality of food?

16.1 Basics Of Food Chemistry

Food provides nutrients these are used by the body as the source of energy. These nutrients also regulate growth, maintain and repair body tissues. The nutrients comprise carbohydrates, lipids, proteins, vitamins, minerals and water. Grains, fruits and vegetables provide carbohydrates and vitamins; meat, fish, eggs, dairy products and pulses provide proteins and vitamins. Lipids are provided by vegetable oils, dairy products and animal fats.

Most nutrients are organic macromolecules. Proteins and carbohydrates are polymeric materials. As a result of food digestion, the polymeric proteins and carbohydrates ultimately break down into monomers, namely, D- amino acids and glucose, respectively, under the influence of enzymes. Cooking makes food easy to digest. During the cooking process, high polymers of carbohydrates or proteins are hydrolysed to smaller polymers. The uncooked food mixture, described as heterogeneous suspension, becomes a colloidal matter on cooking. Because of smaller size of the resulting constituent nutrient molecules, cooked food is easier to digest than the uncooked food.

16.1.2 Food Quality Chemistry

Quality of food is an important aspect of food chemistry. Food quality is described in terms of parameters such as flavour, smell, texture, colour and microbial spoilage. Enzymes are present naturally in all foods.

Teacher's Note

When we cook rice or dal, it becomes soft and tastes better. This happens because cooking breaks down the big food particles into smaller pieces. Just like how you chew your food to break it down, cooking does the same thing.

Exam Trick

Remember: Cooked food has smaller molecules than raw food. Smaller molecules = easier to digest. Think of it like breaking a big chocolate bar into smaller pieces - easier to eat!

Points To Remember

Food gives us nutrients like carbohydrates, proteins, fats, vitamins and minerals.
Cooking breaks down big food molecules into smaller ones.
Smaller molecules are easier for our body to digest and use.
Enzymes help break down food during digestion.
Cooked food becomes a colloidal mixture, not a simple mixture.

Quality of foods changes on shelving mostly due to enzyme action, chemical reactions with the environment and the action of microorganisms. Some of these effects are beneficial. For example, setting of milk into curd and raising flour dough to make bread is brought about by deliberate action of microorganisms. Most changes brought about by microorganisms and interaction with the environment however, adversely affect the food quality.

Problem 16.1

How are the chemical reactions of food stuff with the environment controlled during storage?

Solution

Primarily the oxygen and microorganisms in air are responsible for adverse effects on stored food. The exposure of stored food to atmosphere is minimized by storing them in air tight container, evacuation or filling the container with N₂ gas. Rate of a chemical reaction decreases with the lowering of temperature. Thus refregeration is useful for controlling chemical reaction of food stuff with envrionment. The reactions of food stuff with environment are catalyzed by enzymes. Due to boiling, the enzymes become denatured and the reactions are controlled.

Teacher's Note

When we keep food in the refrigerator at home, it stays fresh longer. Cold temperature slows down the chemical reactions that spoil food. It's like how your body slows down when you are cold.

Exam Trick

Remember: Cold = Slow reactions = Fresh food longer. Enzymes stop working when heated. Think of enzymes like workers - they work fast at room temperature but stop working when it's too hot.

Points To Remember

Oxygen and germs in air spoil stored food.
Air tight containers stop oxygen from reaching food.
Cold temperature slows down food spoilage.
Boiling kills enzymes that cause spoilage.
Using air tight containers and refrigeration helps preserve food.

i. Browning Of Cut Fruit/Vegetables

When fruits such as banana, apple or vegetables such as potato, bottelgourd are peeled and sliced, sooner or later they turn brown. Cutting action damage the cells resulting in release of chemicals. With the pH prevailing in fruit/vegetables, the polyphenols released are oxidised with oxygen in air owing to action from an enzyme to form quinones.

\[{\rm O{-}H \atop} + \frac{1}{2}{\rm O_2} \xrightarrow{{\rm enzyme}} {\rm O \atop O} + {\rm H_2O}\]

A polyphenol → A quinone

Quinones undergo further reactions including polymerization giving brown coloured products named tannins. This browning reaction can be slowed down using reducing agents such as SO₂, ascorbic acid (vitamin C) or by change of pH by adding edible acid such as lemon juice (citric acid) or vinegar.

Teacher's Note

When you cut an apple and leave it on the table, it turns brown. This is like rust forming on iron. Lemon juice stops this browning because it has acid that slows down the chemical reaction.

Exam Trick

Remember: Cut fruit + Air = Brown color. Lemon juice stops this. Think of it as a shield - lemon juice protects the fruit from turning brown. The acid in lemon juice is the key.

Points To Remember

Cutting fruit releases chemicals called polyphenols.
Oxygen in air reacts with these chemicals and an enzyme helps this.
This reaction makes brown colored products called tannins.
Lemon juice or vinegar can prevent browning.
Vitamin C (ascorbic acid) also stops the browning reaction.

ii. Rancidity Of Oils And Fats

On keeping for long time, oils and fats develop an unpleasant or rancid smell and disagreeable taste. Fats are triesters of fatty acids (long chain carboxylic acids) and glycerol (propane - 1, 2, 3 - triol). One cause of rancidity is release of fatty acids produced during hydrolysis of fats brought about by water present in food.

\[{\rm H_2C{-}O{-}C{-}R_1 \atop HC{-}O{-}C{-}R_2 \atop H_2C{-}O{-}C{-}R_3} + {\rm 3H_2O} \xrightarrow{{\rm Hydrolysis}} {\rm H_2C{-}OH \atop HC{-}OH \atop H_2C{-}OH} + {\rm H{-}O{-}C{-}R_1 \atop H{-}O{-}C{-}R_2 \atop H{-}O{-}C{-}R_3}\]

Triglyceride → Glycerol + Free Fatty Acids

The hydrolysis of fats occurs rapidly in the presence of certain microorganisms and is an enzyme catalysed reaction. Rancidity of milk and butter is due to the release of four, six and eight carbon fatty acids (butanoic, hexanoic and octanoic acids) on hydrolysis. Chocolate develops oily or fatty flavour due to release of palmitic, stearic and oleic acids on hydrolysis. Lauric acid on hydrolysis gives a soapy flavour to coconut oil.

Food preservation and food processing methods aim at prevention of undesirable changes and attempt about desirable changes in food. The following cases illustrate some aspects of food quality and the underlying chemisty.

The second cause of rancidity of oils and fats is oxidation by molecular oxygen in the air. Many vegetable oils have one or more C=C double bonds in the fatty acid part of their structure. These are called mono or poly unsaturated fats. The unsaturated fat molecules break down during the oxidation and form volatile aldehydes and carboxylic acids which give the unpleasent rancid taste. This is called oxidative rancidity. It is caused by free radical reaction initiated by light (photo oxidation) or catalysed by either enzymes or metal ions. Polyunsaturated oils containing greater number of C=C double bonds and usually become rancid very quickly. High temperature increases the rate of air oxidation of unsaturated fats. Extensive oxidation can leads to some polymerization with consequent increase in viscosity and browning.

Teacher's Note

Old oil in your kitchen smells bad. This is rancidity. It happens when oxygen touches the oil and breaks it down. Keeping oil in a cool, dark place in a sealed bottle stops this.

Exam Trick

Remember: Old oil = Rancid smell. Rancidity means the oil has gone bad. Keep oil in a cool, dark, sealed container to stop rancidity. Think: No air, no light, no heat = Fresh oil longer.

Points To Remember

Rancidity is when oils and fats go bad and smell bad.
Two types: Hydrolytic rancidity (water breaks fat) and oxidative rancidity (oxygen breaks fat).
Microorganisms also cause rancidity through enzyme action.
Cold temperature and sealed containers prevent rancidity.
Some acids like vitamin C slow down rancidity.

iii. Saturated, Unsaturated And Trans Fats

The long carbon chains of unsaturated fatty acids contain one or more C=C double bonds. This produces one or more 'kinks' in the chain, which prevent the molecules from packing closely together. The van der Waals forces between the unsaturated chains are weak. The melting points of unsaturated fats therefore, are lower.

Natural fats are mixtures of triglycerides. They do not have sharp melting points, and usually melt over a range of temperatures. The more unsaturated the fat lower is its melting point and less crystalline it is. Some examples of fats are given in Table 16.1.

A C=C can have geometrical isomers cis and trans. In the cis form of an unsaturated fatty acid the two hydrogens on the two double bonded carbons are on the same side of the double bond, whereas they are on the opposite sides in the trans isomer. The cis isomer is the most common form of unsaturated fats. The trans form occurs only in animal fats and processed unsaturated fats. Trans fats are difficult to metabolize and may build up to dangerous levels in fatty tissue.

Fats in the form of lipoprotein are used in the body for transport of cholesterol. Excessive low density lipoprotein (LDL) results in deposition of cholesterol in blood vessels, which in turn, results in the increased risk of cardio vascular disease. There is some evidence that eating large amounts of saturated or trans unsaturated fats, increase the tendency of cholesterol getting deposited in blood vessels. Cis fats do not cause formation of such deposits and decrease chance of developing coronary heart disease.

You have noted earlier that fats are triglycerides of fatty acids. Animal fats mostly contain saturated fatty acids, while vegetable oils contain unsaturated fatty acids as well. Long chains of tetrahedral carbon atoms in a saturated fatty acid get packed closely together. Moreover, van der Waal's forces between the long saturated chains are sufficiently strong to convert saturated fats into solid form at room temperature.

Can You Recall?

1. How is Vanaspati Ghee made?

2. What are the physical states of peanut oil, butter, animal fat, vanaspati ghee at room temperature?

Teacher's Note

Ghee is solid at room temperature because it has saturated fats. Oil is liquid because it has unsaturated fats. Your body needs both but too much saturated fat is bad for your heart.

Exam Trick

Remember: Saturated fats = Solid at room temp (like ghee). Unsaturated fats = Liquid at room temp (like oil). Trans fats are bad for health - avoid them. Cis fats are good for health - they are in olive oil.

Points To Remember

Saturated fats are solid at room temperature and found in animal products.
Unsaturated fats are liquid at room temperature and found in plants.
Cis fats are healthy and found naturally in foods.
Trans fats are unhealthy and made by humans.
Too much saturated fat can block blood vessels and cause heart disease.

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