Chemisty

What is limestone mainly made of?
Calcium carbonate.
How is concrete made?
By mixing cement with sand, aggregate and water.
How is cement made?
By heating limestone and clay.
calcium carbonate > ? and what kind of reaction is this?
calcium oxide + carbon dioxide. This kind of reaction is called thermal decomposition.
What is thermal decomposition?
It means ‘breaking down by heating’.
What happens in a rotary lime kiln?
The kiln is filled with crushed limestone and heated strongly using a supply of hot air. Calcium oxide comes out of the bottom of the kiln. Waste gases, including the carbon dioxide made and elements in the air (nitrogen etc.),escape through the top of the kiln.
Why is a stream of hot air used when thermally decomposing limestone?
To ensure the limestone decomposes completely.
What is limestone used for?
Mainly used as a building material.
What is a precipitate?
A solid that is formed in a chemical reaction.
Why do buildings and statues suffer bad damage from acid rain?
Because the calcium carbonate in the limestone reacts with acids. A gas is given off in the reaction.
What happens when a carbonate reacts with acid?
It produces a salt, water and carbon dioxide.
What happens when a metal thermally decomposes?
The metal oxide and carbon dioxide are produced.
What is calcium hydroxide also known as?
Limewater.
What happens when carbon is added the limewater and why?
The limewater turns cloudy because it reacts with carbon dioxide to produce insoluble calcium carbonate. This happens because limewater is alkaline and carbon dioxide gas is weakly acidic.
calcium carbonate + hydrochloric acid >
calcium chloride + water + carbon dioxide.
Why don’t sodium and potassium decompose when heated with a Bunsen burner?
They need higher temperatures to decompose.
Describe the ‘limestone reaction cycle’?
– CaCO3 > CaO + CO2
– CaO + a little H2O > Ca(OH)2
– Ca(OH)2 + more water > Ca(OH)2 solution (limestone)
– Ca(OH)2 solution + CO2 > CaCO3 + H2O
Why do farmers used calcium hydroxide to improve their soil?
Because calcium hydroxide is an alkali and so, can be used to neutralise acids. It can also be used in industry to neutralise acidic gases.
How is lime mortar made and what is it used for?
It is made by mixing cement and sand with water. It is used to hold bricks and blocks together in buildings.
What are the differences between cement, mortar and concrete?
Cement is made from limestone and clay, it is used to make mortar. Mortar is cement mixed with sand and water and is used to hold bricks and blocks together. Concrete is cement mixed sand, water and aggregate used to make blocks, beams, buildings and roads.
Why will lime mortar not set under water?
It prevents it from reacting with CO2
What is a rock that contains enough metal/metal compound to make it worth extracting the metal?
An ore?
What is an ore?
An ore contains enough metal to make it worth extracting the metal.
What do we call the removal of oxygen from a metal oxide?
Reduction.
How can metals be extracted from compounds?
By displacement, using a more reactive element.
finish and balance this equation: PbO + C > ?
2PbO + C > 2Pb + CO2
What is the reactivity series?
A list of elements in order of their reactivity. The most reactive element is put at the top of the list.
What factor do we consider when extracting metals?
The way that we extract a metal depends on its place in the reactivity series.
How are metal more reactive than carbon extracted?
The are extracted using electrolysis.
Why is gold found as the metal rather combined with other elements in compound?
They are so unreactive that they are found in the Earth in their native state.
metal oxide + carbon >
metal + carbon dioxide
What percentage of iron is in cast iron?
96%
Where is iron(III) oxide reduced?
In a blast furnace
Why does iron from the blast furnace have only a few uses?
It is too brittle
Why are steels more useful than pure iron?
They are harder, can be made with specific properties, can be made to resist corrosion
Why does aluminium not corrode easily?
The aluminium atoms at its surface react with the oxygen in the air. They form a thin layer of aluminium oxide. This stops any further corrosion taking place.
What properties make titanium ideal to use in jet engines and nuclear reactors?
It has a combination of strength and low density it can withstand high temperatures and resists corrosion.
What is smelting?
Heating a metal ore in order to extract its metal
What is produced when smelting a copper-rich ore?
It produces impure copper, which can then be purified by electrolysis.
What is phytomining?
Using plants to absorb copper compound from the ground. The plants are burned and produce ash from which copper can be extracted.
What is bioleaching?
Using bacteria to produce solutions containing copper compounds.
Why are new ways of extracting copper being researched?
Hugh-grade ores are limited or running out and so scientists want to find new ways to reduce the environmental impacts.
What is used as the positive electrode in the electrolysis to make pure copper?
Impure copper.
Name 3 properties of transition metals?
good conductors of electricity, strong and can be bent/hammered into useful shapes.
What properties are needed for electrical wiring?
-good conductor of electricity
-can be shaped into wires
-resistant to corrosion
Explain why most of the elements we use are not pure elements?
Most pure metals are too soft for many uses.
Name 3 types of steel and give an important property for each one.
-low-carbon steel: easily shaped
-high-carbon steel: hard
-stainless steel: resists corrosion
Suggest three reasons as to why we should recycle iron and steel.
To save iron ores, to reduce waste going to the landfills and to reduce the amount of fossil fuel needed for the extraction.
What is an alkane and what is an alkene?
Alkane: Saturated hydrocarbon with the general formula CnHn+2
Alkene: Unsaturated hydrocarbon with a carbon-carbon double bond. The general formula is CnH2n.
What happens during fractional distillation?
.
Write a word equation for the complete combustion of propane.
propane + oxygen > carbon dioxide + water
Name four possible products of the incomplete combustion of a hydrocarbon.
Carbon monoxide, water, particulates and soot.
State the two ways in which a hydrocarbon can be cracked.
-by heating a mixture of hydrocarbon vapours and steam to a very high temperature
-by passing hydrocarbon vapours over a catalyst
What happens during a polymerisation reaction?
.
Why can we make polymers from alkenes by not from alkanes?
Alkenes are saturated and are more reactive.
What is a shape-memory polymer?
Shape-memory polymers change back to their original shape when conditions are changed.
What does biodegradable mean?
Materials that can be broken by using microorganisms.
fermentation: glucose > ?
glucose > ethanol + carbon dioxide
hydration: ethene + ? > ?
ethene + steam > ethanol
What is meant by hardening vegetable oils?
Reacting unsaturated oils with hydrogen so that the double bonds become single bonds. This reaction is done at about 60 degrees Celsius using a nickel catalyst.
What is a catalyst?
A substance that increases the rate of a chemical reaction.
Why is the reaction also referred to as hardening?
Because the hydrogenated oils are solid at room temperature.
How do emulsifiers stop water and oil from separating?
Emulsifiers have a hydrophillic part that is attracted to water and a hydrophobic part that is attracted to oil. This keeps them together and prevents them from separating.
What causes tectonic plates to move?
convection currents in the mantle caused by the radioactive decay in the mantle
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