Chemistry science a
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- Created by: leena
- Created on: 12-06-12 18:59
Forming Bonds
Compounds of metas bonded to non-metals have ionic bonds
the formua of an ionic compound shows the simplest ratio of ions
compounds of non-metals have a covaent bonds
3
chemical equations
the mass of the products is equal to the mass of reactants
symbol equation should always be balanced
(learn how to balance an equation)
limestone and its uses
many uses
blocks of limestone can be used for building
limestone is used to make calcium oxide and cement
we make concrete by mixing cement with sand, aggregate and water
limestone is mainly calcium carbonate CaCO3
calcium carbonate decomposes when heated to make calcium oxide and carbon dioxide
this type of reaction is called thermal decompostion
reactions of carbonates
metal carbonates decompose to the metal oxide and carbon dioxide when heated strongly enough
a Bunsen burner flame cannot get hot enough to decompose sodium carbonate or potassium carbonate
all carbonates react with acids to produce a salt, water carbon dioxide gas
limestone is damaged by acid rain because the calcium reacts with calcium carbonate in the limestone reacts with acids in the rain
calcium hydroxide solution is called limewater
liimewater is used to test for carbon dioxide
limewater turns cloudy because it reacts with carbon dioxide to produce insoluble calcium carbonate
fuels from crude oil
crude oil contains many different compounds that boil at different tempretures
these burn under different conditions and so crude oi needs to be separated to make useful fuels
we can separate a mixture of liquids by distillation
simple distillation of crude oil of crude oil can produce liquids that boil within different temperature ranges. these liquids are called fractions.
most of compounds in crude oi are hydrocarbons (hydrogen and carbon)
many of these hydrogen's are called alkanes ( )
alkanes contain as many hydrogen atoms as possible in each molecule and so we call them saturated hydrocarbons
fractional distillation
crude oil is separated into fractions using fractional distillation
the properties of each fraction depends on the size of the hydrocarbon molecules
-inside the column there are many trays with holes to allow gasses through
-the vapours move up the column getting cooler as they go up
-the hydrocarbons condense to liquids when they reach the level that is at their boiling point
-different liquids collect on the trays at different levels and there are outlets to collect the fractions
hydrocarbons with the smallest molecules have the lowest boiling points and so are collected at the top of the column . the fractions collected at the bottom of the column contain hydrocarbons with the highest boiling points
fractions with low boiling ranges have low viscosity so they are runny liquids
they are very flammable so they ignite easily
they also burn with clean flames,producing little smoke.
this makes them very useful as fuels
burning fuels
when pure hydrocarbons burn completely they are oxidised to carbon dioxide and water.
in a limited supply of air incomplete combustion may produce carbon monoxide
carbon may also produced and some of the hydrocarbons may not burn
this produces solid particles that contain soot and unburnt hydrocarbons called particles
most fossil fuels contain sulfur compounds
when the fuels burn these sulfur compounds produce sulfur dioxide
sulfur dioxide produces acid rain
at high tempertures produced when fuels burn oxygen and nitrogen in the air may combine to form nitrogen oxides
nitrogen oxides also produce acid rain
cleaner fuels
burning any fuel that contains carbon produces carbon dioxide
carbon dioxide is a greenhouse gas that many scientists believe is the cause of global warming
incomplete combustion of these fuels produces poisonous gas carbon monoxide
it can also produce tiny solid particles that reflect sunlight and so causes global dimming
exhaust system of cars are fitted with catalytic converters to remove carbon monoxide and nitrogen oxide
alternative fuels
biofuels are made from plant or animal products and are renewable
biodiesel can be made from vegetable oils extracted from plants
biosdiesel advantages: little contribution to carbon dioxide levels because carbon dioxide given off when it burns was taken from the atmosphere by plants as they grew
there are also disadvantages: plants that are grown from biodiesel use large area of farmlands
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