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Science - Unit 1
= = = Acid, Bases and Salts = (The __**THREE**__ important types of chemicals)

Acid
__Definition__:
 * Acid is a substance which when added to water produces hydrogen ions [H+]

__Properties of Acids__:
 * Acids are **sour** in taste (lemons contain citric acid, for example) **DO** **NOT TASTE ACIDS IN THE LABORATORY !!**
 * turn litmus red

__Examples of Acids__: >
 * **Milk** contains **lactic** acid. Lactic acid is named after the Latin word 'lac', which means milk.
 * **Vinegar** is very dilute **acetic** acid. The vinegar used in cooking contains approximately 4% of acetic acid.
 * **Sulfuric** acid is used in the manufacture of many car batteries.
 * **Carbonic acid** is responsible for the 'fizz' in soft drinks. The carbonic acid decomposes into Carbon dioxide bubbles.
 * **Ascorbic** acid is the chemical name of **Vitamin C**. Deficiency of Vitamin C in the body may result in a disease known as scurvy.

Bases
__Definition__:
 * Base is a substance which when added to water produces hydroxide ions [OH-]

__Properties of Bases__:
 * Bases are **bitter** in taste (ever get soap in your mouth?) **DO NOT TASTE BASES IN THE LABORATORY !!**
 * Feel soapy or slippery to touch
 * turn litmus blue

__Examples of Bases__:
 * **Antacids** help to neutralize the acidity (of hydrochloric acid) in the stomach. They chiefly contain two bases, namely Magnesium hydroxide and Aluminum hydroxide
 * **Sodium hydroxide** is also known as '**Caustic Soda**'
 * **Potassium hydroxide** is also known as '**Caustic Potash**'
 * **Ammonia** is a basic gas which is used in the manufacture of fertilizers such as Urea, Ammonium nitrate, and Ammonium sulfate

Salts
__Definition__:
 * A **Salt** results when an acid reacts with a base
 * Both acid and base are neutralised

__Properties of Salts__:
 * Acid + Base = Salt + Water

__Examples of Salts__:
 * **Sodium chloride (NaCl)** is the **common (table)** salt
 * **Sodium carbonate** is used in the manufacture of detergents and glass
 * **Ammonium nitrate** is used in the manufacture of fertilizers

__**pH**__

 * Acidity is measured on a scale called **pH**
 * The value of pH determines how acidic or basic a solution is
 * A substance is **acidic** : if pH is ** less **than 7 ( A pH of 1 is very acidic )
 * A substance is **basic** : if pH is **greater** than 7 (A pH of 14 is a strong alkali)
 * A substance is **neutral** : if pH is **equal** to 7 (A neutral solution //e.g. pure water// has a pH of 7)

** Indicators **
__Definition__:
 * An Indicator is a compound that will change colour in the presence of an acid or base
 * All substances are acidic, neutral or basic (alkaline). How acidic or basic a substance is shown by its pH. There are several other ways by which we could find out whether a substance is acidic, neutral or basic.

__ Examples of Indicators: __ 1. **__ Litmus paper __**
 * ** Red ** litmus turns ** Blue ** in base
 * ** Blue ** litmus turns ** Red ** in acid

2. **__Phenolphthalein pink__** __**pH scale:**__
 * Turns ** Pink ** in Base

Que: How can pH be determined experimentally ? Que: Is human saliva acidic, basic, or neutral?
 * Activities: **