Topic 5 - Seperate Chemistry 1 Flashcards
Explain the physical and chemical properties of transition metals
PHYSICAL:
- high melting point ( except mercury, which is in liquid state at room temperature )
- high density ( they have a high mass for their volume )
- transition metals are stronger and harder than metals in groups 1 + 2 so are often used as construction materials
CHEMICAL:
- formation of coloured compounds
- catalytic activity
Transition metals are often useful as CATALYSTS. These substances increase the rate of a chemical reaction without:
- altering the products of the reaction
- changing chemically
- changing the mass at the end of the reaction
Explain the results of oxidation on metals
The oxidation of metals results in corrosion.
The corrosion of iron and steel is called rusting.
Explain how rusting of iron can be prevented by exclusion
Rust prevention may rely on keeping oxygen and water away from the surface of the iron or steel. Ways to do this includes:
- painting
- using oil or grease
- coating with plastic
- coating with another metal
Rust prevention may keep oxygen away by storing the item in a VACCUM container
Rust prevention may keep water away by putting the item in a container with a desiccant (which absorbs water vapour)
The method chosen depends on factors such as cost and suitability.
Explain how rust can be prevented by sacrificial protection
A metal object can be ELECTROPLATED to:
- improve its appearance
- improve its resistance to corrosion
A thin layer of an unreactive metal such as nickel, silver or gold is deposited on the surface of the metal object, keeping air and water out.
GALVANISATION can also be used. Focuses on the application of molten zinc on a metal surface such as steel.
Explain why converting pure metals into alloys often increases the strength of the product
An alloy is a mixture of a metal with one or more other elements. These other elements are usually other metals or carbon.
In a pure metal, layers of atoms can easily slide over each other. However due to different sized ions in an alloy, this makes it harder for the layers to slide over each other therefore making them stronger.
Explain why iron is alloyed with other metals to produce alloy steels
Pure iron is too soft for most purposes, it is mixed with carbon, and other metals, to produce alloys called steels.
There are many types of steel with different uses depending on their properties. The most common steels are carbon steels. They:
- consist of iron with up to 2.0% carbon
- are harder and stronger than iron alone
Explain how the uses of metals are related to their properties (and vice versa) including aluminium, copper and gold and their alloys including magnalium and brass
IRON is mixed with CARBON to create a hard strong alloy used for buildings, bridges and cars (CARBON STEEL)
ALUMINIUM is mixed with MAGNESIUM to create a low density alloy used for car and aeroplane parts (MAGNALIUM)
GOLD is mixed with COPPER to create an attractive, corrosion resistant (so it stays shiny) alloy used for jewellery (JEWELLERY GOLD)
COPPER is mixed with ZINC to create a hard, corrosion resistant, good electrical conductor alloy used for electrical plugs and coins (BRASS)
Calculate the concentration of solutions in mol dm–3 and convert concentration in g dm–3 into mol dm–3 and vice versa
CONCENTRATION (mol dm-3) = AMOUNT OF SOLUTE (mol) / VOLUME OF SOLUTION (dm-3)
You can also rearrange this to:
- AMOUNT OF SOLUTE = CONCENTRATION X VOLUME
- VOLUME = AMOUNT OF SOLUTE / CONCENTRATION
To convert between:
Mol dm-3 —> g dm-3 = multiply the concentration by the Mr
G dm-3 —> mol dm -3 = divide the concentration by the Mr
In a titration, 25.00 cm3 of sodium hydroxide solution reacts with 24.00cm3 of 0.10 mol dm-3 hydrochloric acid, HCl
Calculate the concentration of the sodium hydroxide solution, NaOH, in mol dm-3
HCl + NaOH —> NaCl + H2O
Volume of HCl = 24.00 cm3 / 1000 = 0.024 dm3
Number of moles of HCl = concentration X volume
= 0.10 mol dm-3 X 0.024 dm3 = 0.0024 mol
From the equation. 1 mol of HCl reacts with 1 mol of NaOH so there will be 0.0024 mol of NaOH
Volume of NaOH = 25.00 cm3 / 1000 = 0.025 dm3
Concentration of NaOH = number of moles / volume
= 0.0024 mol / 0.025 dm3 = 0.096 mol dm-3
Calculate the percentage yield of a reaction from the actual yield and the theoretical yield
Percentage yield = actual yield / theoretical yield X 100
Explain what an actual yield and theoretical yield is
The mass of a product made in a chemical process is called the yield.
In any chemical reaction:
- no atoms are gained or lost
- the total mass stays the same
This means that for a given mass of a limiting reactant, you can only make a maximum mass of a product. This is the theoretical yield.
The actual yield is the mass of a product that you really get at the end of a chemical process. This is always less than the theoretical yield.
Explain reasons for not obtaining the theoretical yield
INCOMPLETE REACTIONS - reactions haven’t finished, reaction reaches equilibrium
SIDE REACTIONS - completing, unwanted reactions, so by-products are also made
PRACTICAL LOSSES DURING THE EXPERIMENT- losses during purification, eg filtration, losses during transfers, eg liquid left behind in containers
Describe what atom economy is
Atom economy is a way of measuring the number of atoms wasted when making a substance.
Describe how to calculate atom economy
ATOM ECONOMY = total Mr of desired products / total Mr of all products X 100
To calculate atom economy you need to know:
- the balanced equation for the reaction
- the relative formula masses, Mr of the products
You can calculate Mr of a substance by adding together the relative atomic masses, Ar for all atoms in its formula.
Describe molar volume
AVOGADRO’S LAW states that equal volumes of all gases, at the same temperature and pressure have the same number of molecules.
This means that one mole of any gas occupies the same volume at a given temperature and pressure.
The value for molar volume Vm9 is:
- 24 dm-3/mol or
- 24000 cm3/mol
