Acids and bases

 

The taste of the food varies because each food item has a unique chemical composition. Based on their chemical nature, substances can be categorized into acids, bases and salts.

Acids:

Acids are compound in which one of the elements that makes up the acid molecule is always the hydrogen   element. For example, hydrochloric acid (HCl).

Substances that contain acids are known as acidic substances. The word acid comes from the Latin word 'acere' meaning sour.

 Types of acids:

Based on the sources they are obtained from, acids are of two types:

A. Organic acids: Acids that are naturally obtained from plants and animal sources are called organic acids.

B. Mineral acids: Acid that are derived from an inorganic material or source are called mineral acids. For example, nitric acid, hydrochloric acid and sulphuric acid.

    Depending upon the amount of water present in acids, they are categorized into concentrated and dilute acids.

A. Concentrated acids: Acids that contain only a small quantity of water are called concentrated acids.

B. Dilute acids: Acids that contain more water than the concentrated acid are called dilute acids. They can be obtained by adding water to a concentrated acid.

Properties of acids:

·   Acids are sour to taste.

·   Acids turns blue Litmus to red.

·    Acids can corrode metals like aluminium and iron due to their corrosive nature. That is why acids are stored in glass containers and not in metal containers.

·    Acids are soluble in water.

Strong acids	Weak acids
Hydrochloric acid Sulphuric acid,  Nitric acid,  phosphoric acid	citric acid,  lactic acid, Acetic Acid,  carbonic acid

Acids are widely used in industries and present in everyday products. Hydrochloric acid which is present in our stomach, help to digest our food. Uses of some acids are given in the following tableUses of acids:

Bases:

Bases  are compounds which contain oxygen or oxygen along with hydrogen. A base that contain oxygen is called an oxide while a base that contains oxygen along with hydrogen is called the Hydroxide.

Substances that contain bases are called basic substances.

Types of Bases:

Based on how  they  take  part in a reaction, bases are of two types: strong bases and weak bases.

A. Strong bases: Some of the bases are corrosive in nature and may result in skin burns. Such bases are called strong bases. For example, Sodium hydroxide, calcium hydroxide and potassium hydroxide.

A. Weak bases: Some of the bases are not corrosive in nature. Such bases are called weak bases. For example, Magnesium hydroxide, Ammonium hydroxide, copper hydroxide.

Properties of bases:

·       Bases are bitter to taste.

·       Bases turn red litmus to blue.

·       Some of the bases are soluble in water they are called alkalis (potassium hydroxide and sodium hydroxide).

·       Bases react with acids to form a salt and water.

Uses of bases:

Sodium Hydroxide is a strong base and it is used to drain cleaners. Strong bases dissolve grease and help in removing dirt.

Uses of some bases are given in the following table

Salts

A salt is formed when an acid and a base react.

The reaction in which acids react with bases resulting in the formation of salt and water are called neutralization reactions.

Types of salts:

A salt can be acidic basic or neutral.

Acidic salts: Acidic salt are formed when strong acids react with weak bases. These salts

have    pH   value   of   less    than 7. 

Basic salts: Basic salt are formed when strong Bases react with weak acids. These salts have

pH   value   of   more    than 7. 

N  neutral   S   alts- formed by the reaction of strong acids and strong bases or weak acids and weak bases  

General Examples of salts- Ammonium chloride  -    NH₄Cl  

aluminium chloride (AlCl₃), Sodium chloride -NaCl

Properties of Salts:

·       Most of the salts are soluble in water.

·       Solution of salts in water act as good conductor of electricity.

·       Some salts are white crystal whereas some are colored. For example, copper sulphate is blue in color and ferrous sulphate is green.

Uses of salts

Neutralization reaction:

When the bases react with acid to produce salt and water. This is a neutralization reaction. In a neutralization reaction, the acid loses its acidity and the base its alkalinity. As a result, a neutral solution is obtained.

Uses of neutralization reactions:

Following are some neutralization reaction that we observe in our everyday life.

In the treatment of ant sting: Some people are highly allergic to ant string as it releases formic acid.

It is neutralized by rubbing moist baking soda (sodium bicarbonate) or Calamine solution, which contains zinc carbonate on the affected area.

In the treatment of indigestion: Hydrochloric acid secreted in the stomach helps in the digestion of food. However, its excess secretion could lead to acidity and indigestion. Milk of magnesia is used to neutralize the acid.

In the treatment of soil: When the soil is too acidic, it is treated with slaked lime or quicklime, which is a base. If the soil is too basic, it is treated with organic matter such as fertilizers that are obtained from vegetables or fruits as they are acidic in nature.

In the treatment of sewage waste: several Industries produce acids as waste. If they are allowed to flow into water bodies, these wastages would affect aquatic organisms.

Slaked lime (Calcium Hydroxide) is often used to neutralize this acidic waste let out from the factories.

 Protecting teeth: One of the best common applications of neutralization of acids is the toothpaste. Toothpastes contain an alkali that neutralizes the weak acid produced by bacteria and prevent tooth damage.

HEAT

 CHAPTER 4     HEAT CLASS NOTE

·    Woollen clothes are obtained from animal fibers. Woollen clothes are generally dark in colour and are worn in the winter season as they protect    us from the cold environment.

· Cotton clothes are obtained from the plant fibres. The  cotton clothes  are generally light in colour and are worn in summer season so that we can feel cool.

Hot and Cold

·   We can understand if an object is hot or cold by the sense of touch. However, it can trick us sometimes. Therefore, we use a thermometer.

·  The temperature of an  object:  It  is  the  degree  of  hotness  or  coldness of an object.

·   Thermometer: It is a device that can be used to find out how hot an object is. In other words, we use a thermometer to measure the temperature of an object.

Measuring the temperature of an object using a thermometer Clinical thermometer

·  It is a device that is used to measure the body temperature of a person.

·  It is made up of a glass tube of uniform thickness.

·  The glass tube contains a bulb at one end which is filled with Mercury.

· The Mercury level in the thermometer rises up in the thread-like  portion of the

thermometer which therefore indicates the temperature of the body.

· The level of the Mercury can be measured by reading the scale given on the

thermometer.

· The scale of the thermometer records the temperature in degree Celsius, generally, 35o C to 45o C, which is the range of human body temperature.

· On an average, the temperature of the human body is around 37o C.

·The clinical thermometer has a small sharp curve (kink) present near the bulb. This

prevents the Mercury level from falling down on its own in the thermometer.

How to use the clinical thermometer?

· Firstly, wash the thermometer with an antiseptic solution.

· Before taking the temperature the thermometer is given a few jerks to bring down the

level of Mercury below 35o C.

·  Then the thermometer is placed beneath the tongue for about a minute.

·  Then you can take it out and observe the temperature reading on the thermometer.

What precautions should be taken while using a clinical thermometer?

·  Wash the thermometer before and after using it.

· Make sure the temperature of the thermometer is below 35o C before taking the

temperature.

·  Keep the thermometer straight in order to see the Mercury level precisely.

·   It should always be held with care or it can break down. You should   not touch the

bulb of the thermometer at all.

Laboratory thermometer

The laboratory thermometer is used to find out the temperature of the other objects such as water rather than human body temperature. It can measure    the temperature from -10o C to 110o C.

What precautions should be taken when using a laboratory thermometer?

Using Laboratory thermometer

·   You should always follow the same precautions as that of the clinical thermometer.

·  You should always hold the laboratory thermometer in a straight upright position without titling it.

·   The bulb of the thermometer should never touch the surface of the container in which the substance is kept.

·  However, the bulb of the thermometer should be completely immersed in the substance so that it covers the bulb from all the sides.

Other types of thermometers

Minimum-maximum thermometer:

It is a thermometer used to measure the minimum and maximum temperature of the day by weather forecasters.

 

Digital thermometer: It is sometimes difficult to handle a Mercury filled thermometer especially when it breaks and the mercury falls out. However, nowadays digital thermometers are available to use. This type of thermometer does not contain Mercury. It directly displays the correct temperature on a display screen.

The transfer of heat

· The flow of heat always takes place from and hot object to a cold object.

A.  Conduction: The process of flow of heat from a hot object to a cold object is called

Conduction. Some objects can conduct heat while others cannot.

·  Conductors: The objects that can allow the heat to flow through them are called Conductors. For Example, metals such as copper and aluminum.

·  Insulators: The objects that do not allow the flow of heat from them are called Insulators. For Example, Wood and Plastic.

    

B. Convection: 

        

· The  transfer   of   heat   in   liquids   and   gases   is   called Convection. The molecules of the liquid or gases that are near the source of the heat get heated first. 

· They become lighter due to the heat and move upwards. 

·   The colder particles being heavier take the place and this process continue until the whole liquid or the gas gets heated. 

         That is why the area above the flame of a candle always feels  hot but the area on the sides of the candle does not.

               Figure 9 Convection

      

C. Radiation: It is a process of transfer of heat in the form of waves. In radiation heat is transferring from one object to another without any medium. 

       For  Example,  the  sun's  heat  reaches  the  Earth’s  surface  through radiation. Every hot object radiates some heat into the environment. Hence, many times an object gets heated just by being near to a hot object.

               Figure 10 Radiation

 

 Sea Breeze and Land Breeze

Sea Breeze

·   The wind blowing from the sea towards the land is called Sea Breeze.

· During the daytime, the land in the coastal area gets heated due to the sun's radiation.

· The sea also gets heated, however it takes more time to get heated up than the land.

·  Hence the air above the land gets heated faster than the air above the sea.

· The hot air from the land rises above as it is lighter  and the cool air from the sea being heavier takes its place. This results in the sea breeze.

Land Breeze

· The wind blowing from the land towards the sea is called the land breeze.

·   During the night time, the land in the coastal areas gets cool down faster than the sea. The air above the sea is hotter than the air above the  land.

·    Therefore the air above the sea rises and the air from the land being cool flows towards the sea. This results in the land breeze

        Why do we wear light coloured clothes in summer?

The light coloured clothes reflect the heat back into the environment and keep us cool during the summer time.

Why do we wear dark coloured clothes in winters?

The dark colour clothes absorb the heat from the environment and keep us warm.

How do woollen clothes keep us warm?

· The woollen clothes are a bad conductor of heat.

·  Therefore they do not allow the heat from the body to move out in the environment.

·   As a result, the air present between the woollen clothes and our body becomes hot and

this makes us feel warm.

·Similarly, two thin blankets provide more heat than one thick blanket because air can be trapped between the two thin blankets.