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chemistry unit 3 - Coggle Diagram
chemistry unit 3
Mr
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So, the total Mr of HCl is 1 + 35.5 = 36.5
To calculate the relative formula mass of a compound, we need to know the relative atomic masses (Ar) of the elements that make the compound. Then we multiply the Ar values by the number of atoms of that element in the compound. Then we add these numbers together.
moles
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number of moles = mass of substance / atomic or formula mass in (g/mol)
eg. moles of carbon dioxide in 33g. 33/44=0.75 moles.
e.g Al2O3-> 2Al+1 1/2O2, calc mass of aluminium ozide to produce 540g of aluminium.
540/27 = 20 mol = aluminium.
20/2 + 10 mol = aluminium oxide
(27x2) + (16 x3) = 102
102 x 10 = 100g mass of aluminium oxide needed.
moles of a gas
volume = amount(mol) x 24dm3. at room temp and pressure one mole of any gas takes up at a volume of 24dm3.
production of ethanol.
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reaction pathway
choosing a pathway:
- atom economy,
- cost of reactants,
- percentage yeild,
- rate of reaction
- equilibrium postition
- usefulness of products
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If this thermometer displayed a reading of 35.4oC, the actual temperature could be anywhere between 35.35oC and 35.45oC.
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The larger the uncertainty, the larger the range of results you should expect.
This is a reason why it is important to repeat the measurements from experiments several times, and calculate an average from them.
half equations
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e.g iron and copper sulfate: Fe(s) -> Fe2+(aq) +2e- loses two electrons to form Fe2+ ions.
Cu2+(aq) +2e- -> Cu(s) Cu2+ ions gain to electrons to form copper atoms.
ionic equations.
simplify equations - show the species that are involved with the reaction and the spectator ions which are not involved in the reaction are not included.
e.g silver nitrate solution added to sodium chloride solution a white precipitate of silver chloride is produced.
AgNO3(aq)+NaCl(aq) -> AgCl(s)+NaNO3(aq) is normal
Ag+(aq) +Cl-(aq) -> AgCl(s)
percentage yeild
not always possible to obtain the calculated amount of product due to: reaction being reversible, product lost when separated from reaction mixture, some reactions may react in different ways to the expected reaction.
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e.g how much calcium oxide can be produced from 50.0kg of calcium carbonate. CaCO3 -> CaO + CO2.
[40+12+(3x16)] -> [40+16]+[12+(2x16)]
100 -> 56 + 44
100:56 (ignore co2 as question doesn't mention it)
100kg of CaCO3 produces 56kg of CaO
so 1kg of CaCO3 produces 56/100 = 0.56kg
and 50kg of CaCO3 produces 0.56 x 50 = 28kg of CaO
atom economy
measure of the amount of reactant that ends up in a useful product. important for sustainable development.
atom economy = realitive formula mass of the desired product / sum of all the relative formula mass of all the products/reactants x 100.
Changing Mass
In chemical reactions, substances may seem to lose or gain mass. Normally, 1 of the reactants (or products) is a gas, and gas can escape into the surrounding environment in a non closed system.
example: magnesium burned in air to produce magnesium oxide. mass increase. when magnesium is burned it combines with oxygen from the air and the oxygen has mass.
2Mg+O2->2MgO. if mass of oxygen is included the total mas of all the product is equal to the reactants.
The molecular formula shows the actual amount of atoms which make up a molecule.
E.g. glucose = C6H12O6
The empirical formula shows the simplest ratio of atoms which make up a molecule.
E.g. glucose = CH2O
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Every chemical measurement made has an uncertainty, and the larger this is, the larger the range of results.