Uss module 5 chpt 7 Food Chemistry

Module 5:Food MattersChapter 7 Food Chemistry

© Copyright Star Publishing Pte Ltd

Chapter 7 Food Chemistry7.1 How are substances extracted and

separated from mixtures?7.2 What is a chemical reaction and what are its applications in daily life?7.3 What are acids and how can they be

identified? 7.4 What are the properties of food acids? 7.5 What is neutralisation and what are its applications in daily life?7.6 What are the effects of untreated wastewater on the environment?


ObjectivesExplain that substances can be

extracted and separated through the following techniques:(i) dissolving (ii) filtration (iii) evaporation (iv) distillation and (v) paper chromatography

Describe the applications of the various separation techniques in homes and food industries

Use a measuring cylinder to measure volume of liquids / solids


Separating Mixtures A mixture is one that contains two

or more different substances that are not chemically combinedtogether.

The food we eat usually consists of mixtures of solids and liquids.

For example, orange juice is made up of orange pulps, sugars, water and many other substances including Vitamin C.

The components in it can be separated using separation techniques.


curry gravy is a rich mixture of spices

a home purification system

for clean drinking water

Separating MixturesSome separation

techniques are:

(a) Dissolving(b) Filtration(c) Evaporation(d) Distillation(e) Paper chromatography


sugar cane juice is extracted from sugar cane stems

Dissolving A mixture of two solids can be separated by using a

solvent which dissolves only one of them.

For example, a mixture of salt and sand can be separated by adding water to the mixture. Salt will dissolve in water but sand will not.

We can obtain sand by filtration of the mixture and salt from evaporation of the filtrate.


separating a mixture of salt and sand

Dissolving of solutesDissolving of solutes is commonly

used at home.

Some examples include:(a) Cooking of soup(b) Drinks sweetener(c) Cleaning of the household


Cooking of soupSoup stock (flavourings) either in solid

or liquid forms, is dissolved in water to flavour the soup.


soup stock is added to water to make soup

Drinks sweetenerSugar is dissolved in drinks (e.g. coffee

and tea) to make the taste better.


sugar is added to water when making tea

Cleaning of the householdDetergent is dissolved in water to remove

dirt from clothes, and clean oily dishes and the floor.


detergent is dissolved in water

Dissolving in the food industries(a) Water is added in the

production of soft drinks, to dissolve the mixture of sweeteners, colourings and flavourings.

Carbon dioxide gas is also dissolved in the drink to create the “fizzy” effect which improves the taste of the drink.


soft drinks contain a mixture of sweetened

flavourings and colourings

Dissolving in the food industries(b) In the production of perfumes, flower extracts such as lavender and rose are dissolved in alcohol to manufacture perfumes.

(c) Chlorine is dissolved in our drinking water and swimming pools to kill harmful bacteria.


perfumes are mixtures ofnatural plant extracts

bacteria in swimming pools are destroyed when chlorine is added

Filtration Filtration is used to separate a

mixture of an insoluble solid from a liquid.

In the diagram on the right, the mixture is poured into a filter funnel with a filter paper.

The filter paper allows the liquid to pass through it but not the insoluble solid particles of the mixture.

In this case, sand left on the filter paper is called the residue and the water that passes through it and collected in the beaker is called the filtrate.


filtration experimental set-up

Filtration At home, filtration is used

in air-conditioners to filter air that may contain dust and smoke particles.

When cooking pasta, the fastest and easiest way to separate the pasta from the boiling water is to pour the contents of the pot into a strainer. This separates the pasta from the water.


a strainer isused to separate the

pasta from water

FiltrationA cup of tea can be made by using a strainer to

prevent tea leaves from entering the cup.


filtering tea from insolubletea leaves

A simple filtration system


Activity Book LinkActivity 7.2Water Purification

Simple filtration system A simple filtration system can be set up to

purify water.

Impurities are removed by passing the water through a bed of sand, gravel and pebbles.

The filtered water can then undergo further stages (e.g. chlorine and UV treatment) to improve the water quality to be fit for drinking.


EvaporationEvaporation is used to

separate a dissolved solid from a liquid. The dissolved solid must not decompose when heated.

For example, salt can be obtained from salt solution by evaporation.

Solid salt will be left behind in the evaporating dish.


water in a salt solutionevaporates, leaving

the salt crystals behind

Decomposition of sugar

Sugar cannot be separated from sugar solution by evaporation because it decomposes and turns black upon heating.


sugar blackens upon heating

Obtaining salt by evaporation

Evaporation is used in salt mines. When temperatures are high, the salt water in the salt pans are evaporated leaving the salt behind. The salt is then piled up to dry.


piles of salt in salt pans

Activity Book LinkActivity 7.3Making Table Salt

CondensationWhen the water boils in the kettle, it changes

into steam. When the steam touches a cold surface, e.g. metal pot or spoon, it cools down and changes into water.

The change from a gas to a liquid is called condensation.


steam from boiling water condenses onthe lid of the container

Distillation Distillation is used to separate a liquid from a

solution. It can also be used to separate a liquid from a mixture of liquids having different boiling points.


distillation experimental setup

DistillationPure water can be obtained from

seawater using distillation.

Distillation can also be used to separate a mixture of ethanol and water.

Ethanol will be distilled first from the mixture because of its lower boiling point 78°C) as compared to water (100°C).


Process of distillation


Activity Book LinkActivity 7.4Simple Distillation

Chromatography Chromatography is a method of using a solvent to

separate a mixture into its components.

Food colourings are often used to improve the appearance of our food and drinks. Food colourings are usually a mixture of coloured dyes.

Chromatography can be used to test if the dyes in food colourings are safe for consumption. Chromatography can also be used to detect banned drugs in urine samples


Paper chromatography(a) A small drop of ink is placed on one end of the chromatography paper.

(b) When this end of the chromatography paper is soaked in a solvent, the solvent travels up the paper, carrying with it the dyes in the ink.


separating ink using chromatography

Activity Book LinkActivity 7.5Investigating the Components of Food Dyes

Paper chromatography(c) There are two coloured spots formed on the chromatogram. This shows that the ink sample is a mixture and it contains two different coloured dyes.

(d) The dyes that are more soluble will move faster and further up the chromatogram whereas the dyes that are less soluble will move slower and form spots at lower positions.


different coloured dyes

appear on the chromatogram afterthe ink has dissolved

in the solvent

Chapter 7 Food Chemistry7.1 How are substances extracted and separated

from mixtures?7.2 What is a chemical reaction and what

are its applications in daily life?7.3 What are acids and how can they be



ObjectivesDescribe a chemical reaction as a process

that leads to the formation of new productsGive examples of everyday changes that

involve chemical reactions : (i) decaying of food (ii) burning (iii) rusting (iv) cooking of food

Give examples of everyday situations in slowing down / preventing chemical reactions (e.g. Preserving food, reducing amount of heat, fuel and air supply for burning, tin plating against rusting)


What is a chemical reaction?Chemical reactions happen around

us and even inside us.

Digestion of food is an example of a chemical reaction and is an important process before we can derive energy from food.

All chemical reactions lead to new products being formed.


Chemical reactions in everyday life


Ways to slow down chemical reactions









from mixtures?7.2 What is a chemical reaction and what are its applications in daily life?7.3 What are acids and how can they be



ObjectivesDescribe the properties of acids by

their taste and effects on litmus paper and universal indicator

Describe acidity, neutrality and alkalinity in terms of the pH scale (whole numbers only)

Measure the pH of various common household substances and food using homemade pH indicator, litmus paper, universal indicator and a pH meter


Properties of Acids Acids are present in

everyday items. Acids can be identified by the following properties:

(a) Sour taste

Lemons, oranges and grapefruits containan acid called citric acid which gives them their sour taste. Vinegar tastes sour because it contains ethanoic acid.


foods containing acids

Properties of Acids(b) Turns blue litmus paper red

When both red and blue litmus papers are placed in an acidic solution (e.g. lemon juice), the blue litmus paper turns red, while the red litmus paper remains red.


blue litmus turns red in acid while red

litmus paper remains unchanged

Properties of Acids(c) Acids also produce colour change in universal

indicator. The table below shows the colour change of the universal indicator when tested with some sample substances which are acidic.


Colour changes of the universal indicator in different acid conditions


The pH ScalepH is a measure of the strength of an

acidic or alkaline solution.

The pH scale is a range of numbers from 0 to 14 that shows how acidic, alkaline or neutral a substance is.

Neutral solutions have a pH of 7.

Acidic solutions have pH values of less than 7.


The pH ScaleA solution with a lower pH is more acidic

than one with a higher pH.

Alkalis have pH values of more than 7.

A solution with a higher pH is more alkaline than one with a lower pH.


The pH scale


Activity Book LinkActivity 7.6Testing for Acids

IndicatorsIndicators can be used to test for

the presence of acids and alkalis.

An indicator will change colour depending on whether the solution tested is acidic or alkaline.

There are many types of indicators commonly used in the laboratory to indicate the pH of solutions.


Litmus indicator The commonly used litmus

indicators are the red and blue litmus.

Litmus is a dye obtained from plants and can be used as a solution or in paper form.

Blue litmus turn red in acidic solutions, and red litmus turn blue in alkaline solutions.

In neutral solutions, both the red and blue litmus will not change colour.


litmus solution and litmus paper

Natural indicatorsSome flowers, vegetables and berries

can be used as natural indicators.

For example, the coloured juice extracted from the red cabbage turns pink when tested with acidic substances and green when tested with alkaline substances.

Other examples include extracts from grape peels and orchid flowers.


Natural indicators


red cabbage juice is a natural indicator as it changes colour in

different pH

berries, grapes and are natural indicators

orchid flowers are natural indicators

Universal indicatorThe universal indicator is a mixture of several

different types of indicators. It can show a variety of colours depending on how acidic or alkaline a substance is.

Each colour corresponds to a pH value. The universal indicator is used in the form of a solution or a paper.

The pH of the acid of or alkali can be determined by comparing the colour of the universal indicator against the colour chart.


Universal indicator solutionand universal indicator paper


pH meterA pH meter is an instrument used to

measure the pH of a substance accurately.

A pH meter consists of a pH probe which is connected to a datalogger.

A pH probe is placed in a solution to determine its pH value and the pH value of the solution is recorded on the datalogger.

Among the four indicators, the pH meter gives the most accurate pH reading of a solution.


pH meter can measure anaccurate pH reading of a solution



from mixtures?7.2 What is a chemical reaction and what are its applications in daily life?7.3 What are acids and how can they be identified? 7.4 What are the properties of food acids? 7.5 What is neutralisation and what are its applications in daily life?7.6 What are the effects of untreated wastewater on the environment?


ObjectivesDescribe the characteristic

properties of food acids on the following items that are commonly found at home(i) metals ( e.g. cooking utensils )(ii) bases ( e.g. antacids )(iii) carbonates ( e.g. baking soda, effervescent Vitamin C tablets)


Reaction of Food Acids with Metal UtensilsSome common examples of acids found in food

are lemon and orange juice (citric acid), tea (tannic acid) and soft drinks (carbonic acid).


lemons contain citric acidsoft drinks contain carbonic acid

Acid reaction with metals Acids react with some metals to produce a salt

and hydrogen gas.

For example, when some magnesium strips are added to a test tube of lemon juice, bubbles can be observed to form on the magnesium strips.

The bubbles on the magnesium strips are hydrogen gas.

The presence of hydrogen gas can be tested using a lighted splint. Hydrogen gas will extinguish a lighted splint with a “pop” sound.


Testing for hydrogen gas


Acid reaction with metals The general word equation to represent the reaction of a

metal with acid is:

acid + metal salt + hydrogen gas

Most cooking utensils are made of metal.

Over time, these utensils may become rusty. The rust can be removed by soaking the rusty utensils in vinegar or rubbing them with lemon slices.

The acid in the vinegar or lemon will react with the rust to form a soluble substance that can be easily washed off.


rusty utensil

Reaction of Food Acids with CarbonatesAcids react with carbonates to give off

carbon dioxide gas.

Some examples of carbonates found in or daily life are baking powder, egg shells, Vitamin C tablets and sea shells.

For example, when some egg shells are added to vinegar, bubbles of gas can be observed to form on the egg shells.

The bubbles formed are carbon dioxide gas. © Copyright Star Publishing Pte Ltd

Testing for carbon dioxideThe presence of carbon dioxide gas can be

tested by bubbling it into limewater.

If carbon dioxide gas is present, the limewater will turn chalky.


Reaction of Food Acids with Carbonates

Vitamin C tablets consist of an acid and a carbonate. When the tablet is added to water, the acid and carbonate dissolve and react to produce carbon dioxide gas which results in the fizzy bubbling effect

Baking powder contains sodium bicarbonate (baking soda) and an acid. During baking, the baking soda and the acid present in the baking powder react to produce carbon dioxide gas. This gas helps to raise the cake and makes it soft.


Reaction of Food Acids with CarbonatesThe general word equation to

represent the reaction of a carbonate with acid is:

acid + carbonate salt + carbon dioxide

+ water


Reaction of Food Acids with BasesAcids react with bases to produce a salt and

water.

Bases dissolve in water to form alkalis. For example, our stomach produces an acid which helps us in the digestion of food.

At times if we eat too much and too fast, the acid may flow backwards into our oesophagus.

We may feel a burning sensation. This is called acid reflux or heartburn.


Backflow of stomach acid into oesophagus causes heart burn


Antacids If we do not have regular

meals, the acids produced in our empty stomach may cause us to suffer from gastric pains.

Over time, this may cause damage to the inner walls of the stomach.

Antacids, which contain a base, can be used to neutralise the excess acid. This process is called neutralisation.


antacids neutralise stomach acid

Activity Book LinkActivity 7.7Properties of Acids


from mixtures?7.2 What is a chemical reaction and what are its applications in daily life?7.3 What are acids and how can they be identified? 7.4 What are the properties of food acids? 7.5 What is neutralisation and what are its applications in daily life?7.6 What are the effects of untreated wastewater on the environment?


ObjectivesState that neutralisation takes place

when an acid reacts with a base and the products are salt and water only

State some applications of neutralisation (e.g. action of tooth paste, fabric softener and hair conditioner, controlling of pH in soil, neutralising industrial wastes)

Relate pH within the mouth to its effect on dental health


Neutralisation Neutralisation occurs when an acid reacts with a base

to produce a salt and water only.

The general word equation to represent neutralisation is:

acid + base → salt + water

For example, mixing sodium hydroxide and hydrochloric acid produces two new substances, sodium chloride and water.

The word equation is:


Neutralisation If sulfuric acid is used, the word equation

becomes:

Sodium chloride and sodium sulfate are salts.

Neutralisation reactions are important because there are many useful daily applications for them.


Useful applications of neutralisation reactions in everyday life








Activity Book LinkActivity 7.8Neutralising Chemical Waste

Chapter 7 Food Chemistry7.1 How are substances extracted and

separated from mixtures?7.2 What is a chemical reaction and what are

its applications in daily life?7.3 What are acids and how can they be

identified? 7.4 What are the properties of food acids? 7.5 What is neutralisation and what are its applications in daily life?7.6 What are the effects of untreated

wastewater on the environment?© Copyright Star Publishing Pte Ltd

ObjectivesState some of the effects of

phosphate detergents (e.g. increase growth of algae and water weeds) and acidic wastewater on the rivers and seas

Understand the use of microbes in sewage plants to treat the wastewater before they are released to the rivers and seas


Effects of Untreated Sewage on the Environment








What are microbes and their uses? Microbes such as bacteria are nature’s “recyclers”.

They can break down bodies of dead animals and plants into simpler substances.

Bacteria are very useful in the treatment of waste water because they produce enzymes to break down the waste substances into smaller and simpler substances.

The bacteria population is also well regulated as they grow quickly when there is a lot of “food” for them.

When the “food” supplies decrease, the bacteria population will decrease rapidly.


Microbes and their uses


magnified view of thebacteria

scientists analysing bacterial colonies multiplying on “waste materials” as their source of

food

Sewage treatment In sewage treatment plants, microbes such as aerobic

bacteria are used to decompose the waste sewage material.



Education

Uss module 5 chpt 7 Food Chemistry