Food Chemistry - Coggle Diagram
What are acids and how can they be identified?
Properties of Acids
Lemons, oranges and grapefruits contain an acid called citric acid.
Vinegar tastes sour because it contains ethanoic acid.
We should not taste any unknown substance to determine if it is an acid.
turns blue litmus paper red
When both red and blue litmus papers are placed in an acid solution, the blue litmus paper turns red, while the red litmus paper remains the same.
Acids produce colour change in universal indicator.
4, Green to Yellow-orange
3, Green to Orange
1, Green to Orange-red
the pH Scale
it is a measure of the strength of an acidic or alkaline solution.
It is a range of numbers from 0 to 14 that shows how acidic, alkaline or neutral a substance is.
Acidic solutions have a pH values of less than 7
Alkalis solutions have a pH values of more than 7
Neutral solutions have a pH of 7.
It can be used to test for the presence of acids and alkalis
It will change colour depending on whether the solution tested is acidic or alkaline
It is a dye obtained from plants and can be used as a solution or in paper
Blue turns red (Acid)
Red turns blue (Alkaline)
Neutral remains the same
Some flowers, vegetables and berries can be used as natural indicators
Ex: Coloured juice extracted from the red cabbage turns pink when tested with acidic substances
Ex: and green when tested with alkaline substances
It is a mixture of several different types of indicators.
This shows a variety of colours depending how acidic or alkaline a substance is.
Each colour corresponds to a pH value
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it is an instrumental used to measure the pH of the substance accurately.
it consists of a pH probe which is connected to a datalogger.
it is placed in a solution to determine its pH value and the pH value of the solution is recorded on the datalogger.
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What are the properties of food acids?
Reaction of Food Acids with Metal Utensils
Acid reacts with some metals to produce a salt and hydrogen gas.
Ex: 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 strip are hydrogen gas
its presence can be tested using a lighted splint
Hydrogen gas will extinguish a lighted splint with a "pop" sound.
It shows that it is produced when food acid, in this case acid from the lemon juice, reacts with metal.
Acid + metal → salt + hydrogen gas
Most cooking utensils are made of metal.
over time, these utensils may become 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
Reaction of Food Acids with Carbonates
Acid reacts with carbonates to give off carbon dioxide gas.
Ex: baking powder, egg shells, vitamin c tablets, sea shells...
Ex: when 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.
its presence of carbon dioxide gas can be tested by bubbling it into limewater.
If it is present, the limewater turns chalky.
Vitamin C tablets consists 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.
The carbon dioxide gas results in the fizzy bubbling effect.
Baking powder contains sodium bicarbonate and an acid.
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.
Acid + Carbonate → Salt + Carbon Dioxide + Water
Reaction of Food Acids with Bases
Acids react with bases to produce a salt and water.
Bases dissolve in water to form alkalis
Ex: Our stomach produces an acid which helps us in digestion of food.
Eating too much and too fast can cause the acid to flow backwards into our oesophagus
We may feel a burning sensation.
this is called acid reflux or heartburn
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.
What is a chemical reaction and what are its applications in daily life?
It happens 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.
Chemical reactions lead to new products being formed
It caused by microbes
Food when left in the open will start decay after some time.
microbes such as bacteria, yeast, and mould will grow on the food and cause it to spoil.
to prevent or slow it down...
Lowering of pH
pH is lowered to make the food acidic so as to reduce or prevent microbial activity.
Reducing food water content
Water content in the food can be reduced by drying it under the sun or in a heater,
Without moisture, microbes cannot live and multiply
It kills or destroys most microbes present in milk.
In chillers and freezers, it slows down the growth of microbes.
Reducing air supply
Most air in the food packaging has been removed.
This will slow down the growth of microbes in food
It is a chemical reaction that reacts with air and water.
To prevent or slow it down...
Paint over metal surfaces prevent oxygen and moisture from the direct contact.
Apply a layer of grease or oil on metal surfaces such as nails or ball bearings as it can prevent oxygen and moisture from direct contact.
Food cans are made of steel and plated with a layer of tin.
It prevents oxygen and moisture from coming into contact with steel.
When paper is burned with oxygen, ashes and carbon dioxide gas are formed
It is called combustion
Most food needs to be cooked before it is safe to be eaten.
Heat is supplied to food to ensure that all the microbes have been destroyed by high temperatures and that the food is cooked before it can be eaten.
To prevent or slow it down, reducing air supply will slow down the burning and cooking of food.
Reducing fuel and heat will also slow down the burning and cooking of food.
What is neutralisation and what are its applications in daily life?
Acid + Base → Salt + Water
Ex: hydrochloric acid + sodium hydroxide → sodium chloride + water
sulfuric acid + sodium hydroxide → sodium sulfate + water
Examples of neutralisation reactions
Controlling pH in soil
Acid rain can affect the growth of crops.
Some plants grow well in acidic soil, while other plants grow well in alkaline soil.
Farmers have to ensure that the soil pH is suitable for the type of crops they want to grow.
If the soil is too acidic, farmer can mix calcium hydroxide to soil to neutralise the acid in it.
Farmers will need to add acidifiying fertilisers to increase the acidity of the soil.
Neutralising industrial waste
Factories may discharge gaseous wastes such as smoke, into the atmosphere or liquid wastes into rivers and seas.
These wastes can be acidic or alkaline in nature.
They need to be neutralised before they can be released into the environment to prevent air and water pollution.
Preventing tooth decay
Bacteria in the mouth produce acid when food particles are trapped between the teeth.
It will cause tooth decay when not removed.
toothpaste contains a base so it helps to neutralise the acid on the teeth when we brush our teeth.
Excess acid in our stomach may cause gastric pain and discomfort
This can be relieved by taking some indigestion medicine (or antacids) which contain a base.
The base in the indigestion medicine neutralises the excess acid in the stomach.
The detergent used to wash our laundry are alkaline in nature.
it contains mild acid which will neutralise the detergents in washing so it will bring the texture and feel of the fabric back to its original condition.
Shampoos are usually alkaline in nature so after using them to wash our hair, it makes our hair feel dry.
Conditioners can be applied onto our hair often after we have washed it with shampoo.
It contains mild acid which will neutralise the alkalis in shampoos to make our hair feel soft and smooth.
To curl hair, an alkaline solution is used to soften the hair so that it can take shape of hair curlers.
the curling solution is neutralised in an acidic solution.
What are the effects of untreated wastewater on the environment?
These untreated wastes pollute water and pose a danger to the aquatic plants and animals living in the water.
Some detergents contain phosphate.
When a large amount of untreated phosphate detergent is washed into the sewage and into the rivers and lakes, the growth of algae and weeds growth will increase very quickly.
It is impossible to remove it, even there are treatments.
Using non-phosphate detergents and treating the sewage wastewater before releasing it into the rivers and lakes can help prevent contamination.
Untreated liquid and solid wastes from houses and factories are discharged into seas, rivers and lakes.
It covers the surface of the lakes and rivers and prevents sunlight from reaching the bottom of the water bodies.The aquatic plants in the water cannot carry out photosynthesis.
Over time, the oxygen levels in the water will decrease.
it will cause the aquatic animals and plants to die eventually.
Discharging untreated acidic waste water into rivers and lakes will affect the pH of the water.
aquatic animals and plants generally survive well in water with neutral pH.
Acidic waste water condition is unsuitable for marine life.
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.
Its population is also well regulated as they grow quickly when there is a lot of "food" (waste substances) for them.
When the "food" supplies decrease, the bacteria population will decrease rapidly.
In sewage treatment plants, microbes such as aerobic bacteria are used to decompose the waste sewage material.
How are substances extracted and separated from mixtures?
A mixture is one that contains two or more different substances that are not chemically combined together
The food we eat usually consists of mixtures of solids and liquids.
The orange juice is made up of orange pulps, sugars, water and many other substances, including vitamin C.
The orange juice is a mixture
Although it is freshly squeezed from the fruit and no other substances have been added to it, the components in it can be separated using separation techniques.
A mixture of two solids and be separated by using a solvent which dissolves only one of them.
A mixture of salt and sand can be separated by adding water to mixture.
Salt can dissolve in water but sand will not
We can obtain sand by filtration of mixture and salt from evaporation of the filtrate
Dissolving of solutes is commonly used at home.
Cooking of soup
Soup stock (flavourings) either in solid or liquid forms, is dissolved in water to flavour the soup
Sugar is dissolved in drinks (e.g. coffee and tea) to make the taste better
Cleaning of the household
Detergent is dissolved in water to remove dirt from clothes, and clean oily dishes and the floor.
Dissolving water is also widely used in the food industries.
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 create the "fizzy" effect which improves the taste of the drink.
In the production of perfumes, flowers extracts such as lavender and rose are dissolved in alcohol to the manufacture perfumes
Chlorine is dissolved in our drinking water and swimming pool to kills harmful bacteria
It is used to separate a mixture of an insoluble solid from a liquid.
The mixture is poured into a filter tunnel with a filter paper.
It allows the liquid to pass through it but not the insoluble solid particles of the mixture.
The 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.
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.
Similarly, a cup of can be made by using a strainer to prevent tea leaves from entering the cup.
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.
It is used to separate a dissolved solid from a liquid.
The dissolved solid must not decompose when heated
Ex: Salt can be obtained from salt solution by evaporation
When the salt solution is heated until all the water in the solution has evaporated, the solid salt will be left behind in the evaporating dish.
Sugar cannot be separated from sugar solution because it composes and turns black upon heating.
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
It is used to separate a liquid from a solution.
It can be also be used to separate a liquid from a mixture of liquids having a different boiling points.
When 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.
Pure water can be obtained from seawater using the method
The set-up shows how distillation can be used to obtain pure water from seawater
Distillation can also be used to separate a mixture of alcohol and water.
Ex: Ethanol (a type of alcohol) will be distilled first from the mixture because of its lower boiling point (78°C) as compared to water (100°C)
Steam is produced
Solution (e.g. seawater) or mixture of liquids with different boiling points (e.g. alcohol and water mixture).
Pure liquid with the lower boiling point will be distilled and obtained first.
It is a method of using a solvent to separate a mixture (e.g. food colourings, inks or dyes) into its coloured components.
It shows the set-up for separating ink (containing a mixture of different coloured dyes) using a paper chromatography
A small drop of ink is placed on one end of the chromatography paper
When this end of chromatography paper is soaked in a solvent, the solvent travels up the paper, carrying with it the dyes in the ink.
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
The dyes that are more soluble will move faster and further up the chromatogram whereas the dyes that are less soluble will move slower form spots at lower positions
Food colouring are often used to improve the appearance for our food and drinks.
It is usually a mixture of coloured dyes
Chromatography can be used to test if the dyes in food colourings are safe for consumption.
It can be also be used to detect banned drugs in urine samples.