known as the first caliph.
Christians, Jews, and Muslims all see Abraham
as an important religious figure. A
painting shows Abraham during his journey
to Canaan.
Abu Bakr (second from left) was an
important Islamic leader.
14 Absaroka BRITANNICA STUDENT ENCYCLOPEDIA
Abu Bakr was born in the Arabian town
of Mecca (now in Saudi Arabia), which
was also the birthplace of Muhammad.
His daughter !A#ishah became one of
Muhammads wives.
While Muhammad was dying, he called
upon Abu Bakr to lead prayers and pilgrimages
in his place. By that time
Muhammad was more than the religious
leader of the Islamic lands; he was their
political ruler as well. After Muhammad
died in 632, Abu Bakr ruled as caliph.
Caliph means successor (one who
comes afterward). The Islamic lands
were called the Caliphate.
As caliph, Abu Bakr fought wars against
Arabian tribes who rebelled against him.
He soon brought the tribes of Arabia
under Muslim rule. Abu Bakr then sent
armies into what are now Syria and Iraq.
This began a series of conquests that
spread Islam far beyond Arabia. Abu
Bakr died in 634.
..More to explore
Caliphate Islam Mecca
Muhammad
Abu Dhabi
Population
(2007 estimate)
633,140
Abu Dhabi is the capital of the United
Arab Emirates, a union of Arab states on
the Arabian Peninsula. It is also the capital
of Abu Dhabi kingdom, the largest of
the seven states.
The city of Abu Dhabi occupies most of
a small triangular island in the Persian
Gulf. The island is connected to the
mainland by a short bridge.
Local tribesmen settled Abu Dhabi in
1761. Through most of its history the
town remained small and undeveloped.
This changed when rich oil fields were
discovered in Abu Dhabi in 1958. Oil
revenues were used to modernize the
town. Electricity, running water, and a
central sewage system were installed.
Modern buildings and a new port were
built.With modernization, the population
grew.
The United Arab Emirates gained independence
from Great Britain in 1971.
Abu Dhabi became the permanent capital
of the federation in the early 1990s.
..More to explore
United Arab Emirates
The Sultan Zayed Mosque in Abu Dhabi
was named for a longtime ruler of the
United Arab Emirates. The sultan was buried
in the mosque when he died in 2004.
BRITANNICA STUDENT ENCYCLOPEDIA Abu Dhabi 15
Abuja
Population
(2006 census),
Federal Capital
Territory,
1,405,201
Abuja is the capital of the African country
of Nigeria. It was built in the 1980s
to replace the crowded coastal city of
Lagos as the capital.
Abuja is located near the center of Nigeria
in an area called the Federal Capital
Territory. It is about 300 miles (480
kilometers) northeast of Lagos. The city
is built on the grass-covered Chukuku
Hills. The climate is cooler and less
humid than that of Lagos.
Abuja is divided into two zones. The
central area contains the government
buildings. The other zone provides
housing, shopping facilities, and other
services for the people who live there.
The government started planning the
new city of Abuja in 1976. It took more
than 10 years to build the city, but the
population grew even before it was finished.
Abuja officially became the capital
in 1991.
..More to explore
Nigeria
Accra
Population
(2003 estimate)
1,847,432
Accra is the capital and largest city of the
West African country of Ghana. Its
name comes from the word nkran in the
Akan language. This refers to the black
ants that thrive in the area. Accra is situated
on the Gulf of Guinea.
Accra is the site of Ghanas main government
offices. It is also the economic
center of Ghana. It contains the head
offices of all the countrys large banks
and trading firms. The city also has large
open markets. Its main products are
processed food, lumber, and textiles.
The city of Accra was formed in 1877.
By that time the British had gained control
of the whole area. It became known
as the colony of the Gold Coast. Accra
was the capital of the colony. The modern
city of Accra was carefully planned
and laid out between 1920 and 1930.
The Nigerian presidential palace is located
in the hills of the countrys capital, Abuja.
16 Abuja BRITANNICA STUDENT ENCYCLOPEDIA
When the Gold Coast gained independence
as Ghana in 1957, Accra
remained the capital.
#More to explore
Ghana
Acid and Base
Acids and bases are two related groups of
chemicals. They are important to living
things and have many uses in industry.
Acids
Some acids are found in food. They
include acetic acid in vinegar, lactic acid
in milk, and citric acid in lemons. They
often have a sour taste. Other acids are
found in animals. The stomach makes
an acid that helps break down food.
Some acids do not come from living
things. These can be so strong that they
can corrode, or break down, metals.
They should not be tasted or touched.
Sulfuric acid is one example. It is used to
make fertilizers, dyes, drugs, explosives,
and certain batteries. When an acid is
dissolved in water the result is called an
acidic solution.
Bases
Bases may feel slippery in water. Some
are used in foods or medicines. These
often have a bitter taste. Examples of
bases include baking soda and milk of
magnesia. Other bases are used in
manufacturing. These are too strong to
be tasted or touched. Sodium hydroxide,
or lye, breaks down animal and plant
tissues. It is used to make soap, paper,
and artificial fibers. When water is combined
with a base the result is called a
basic, or alkaline, solution.
Acid-Base Reactions
When acids and bases are combined
they produce water and compounds
called salts. They have a salty taste and
none of the characteristic properties of
either acids or bases. The reactions
between acids and bases can be quite
strong. One result is that they can
quickly produce gases. This is why baking
soda is useful for baking pastries and
cakes. When it is combined with an acid
such as lemon juice or sour cream in a
dough mixture, it releases gases that
make the dough rise.
Identifying Acids and Bases
Acids and bases make some materials
change color. A special kind of paper
called litmus paper is one type of mate-
A strip of litmus paper shows
that a solution contains an acid.
If the solution contained a base
the paper would have turned
blue.
BRITANNICA STUDENT ENCYCLOPEDIA Acid and Base 17
rial that does this. An acid in water turns
litmus paper red. A base in water turns
the paper blue. A neutral substance,
such as pure water, gives litmus paper a
color midway between red and blue.
Acid Rain
Acid rain is a form of air pollution.
When coal and petroleum are burned in
automobiles, electric power plants, and
factories, they release certain harmful
gases into the air. These gases combine
with the oxygen and water in the air.
When the water in the air comes down
as rain, sleet, hail, or snow, it carries
with it these gases. This is known as acid
rain. Acid rain is very damaging to all
life forms.
Acid rain can pollute lakes and streams,