ACID and ALKALIS

Lemon juice and vinegar taste sour because they contain weak acids.An acid is a substance that dissolves in water to form positively charged particles called hydrogen ions (H+). The opposite of an acid is an alkali, which dissolves in water to form negatively charged ions of hydrogen and oxygen, because they cancel out acidity. Toothpaste, for example, contains an alkali to cancel out acidity in the mouth that would otherwise damage teeth.









pH scale
The concentration of hydrogen ions in a solution is known as its pH. Scientists use the pH scale to measure acidity and alkalinity. On the pH scale, a solution with a pH lower than 7 is acidic, and a solution with a pH greater than 7 is alkaline. Water is neutral, with a pH of 7. A solution's pH can be tested with universal indicator solution or paper, which changes colour in acids alkalis.

Strong acids 
 The more hydrogen ions an acid form in water, the stronger it is, and the lower its pH. Strong acids, such as sulphuric acid and nitric acid, are very dangerous and must be handled carefully.
Sulphuric acid 
Concentrated sulphuric acid will dehydrate (remove water from) any substance with which it comes into contract. For example, the acid dehydrates sugar, a carbonhydrate, to leave a mass of smouldering black carbon. 
Nitric aacid
Organic matter, such as paper, cork, rubber, fabric, and skin, is rapidly decomposed by nitric acid.The acid is so corrosive because it oxidizes (supplies oxygen to) any material with which it comes into contact.
 

ABOIGINAL AUSTRAILANS

The ABORIGINALS settled the Australian continent more than 40,000 years ago. They lived in total isolation from the rest of the world, existing by hunting and gathering. In the 18th century, the Europeans arrived,forcing the Aboriginals off their territories. Today, many feel isolated from white society, but still try to preserve their tribal identity.

Ways of life 
 Traditionally, Aboriginals lived by hunting and gathering. They were nomadic, roaming over large stretches of territory, setting up temporary camps near watering places, and moving on when food  supplies were exhausted. They traded eith other tribes, exchanging goods such as spears.

Dreamtime
The aboriginals believe that Dreamtime is a period when Ancestral Beings shaped the land, creating all species and human beings. These beings are believed to be a part of nature, closely associated with all other living things. Images of spirits of Dreamtime, such as lightning Man, cover scared cliffs and caves in tribal areas.





Uluru (Ayers Rock) 
Aboriginals believe that the Ancestral beings created the Australian landscape, and established customs and traditions still followed today. They have left evidence of their presence in the many scared places,such as Uluru in central Australia. This is revered as a scared place by the local Aranda people.Once called Ayers Rock by the Australian government, the rock regained its Aboriginal name in 1988. 

Hunters and Gathering
Aboriginals lived by hunting animals such as kangaroos, and supplemented their diet with wild plants, nut, and berries. The hunters used spears with stone blades and wooden  boomerangs, a type of missile that flies back to the thrower . Some tribes developed an elaborate sign language, so that they could send silent messages to each other when they were stalking game.