Friday, November 27, 2009

state symbol -IGCSE/ GCSE NOTES

State symbolsThe state symbols are put in a balanced equation to show whether something is a solid, liquid, gas or dissolved in water (aqueous solution).
The symbols for these are:
state
Symbol
Solid
(s)
Liquid
(l)
Gas
(g)
Aqueous
(aq)
Magnesium + oxygen --> magnesium oxide
2Mg{s} + O2{g} --> 2MgO{s}
hydrochloric acid + calcium carbonate --> calcium chloride + carbon dioxide + water
2HCl (aq) + CaCO3 ---> CaCl2(aq) + CO2(aq) + H20(l)
Balanced equations and ionic equations

Ionic equations only show ions which change in a reaction and ignore those which do not change. E.g.word equation
hydrochloric acid + sodium hydroxide --> sodium chloride + water
balanced chemical equation
HCl(aq) + NaOH(aq) ---> NaCl(aq) + H2O(l)
ionic equationH+(aq) + OH-(aq) ---> H2O(l)
E.g. in the electrolysis of sodium chlorideCl-(aq) --> Cl(g) + e-2Cl(g) --> Cl2(g)
Working out formulae from reacting masseselements reacting magnesium chlorinesymbols of elements Mg Clmasses reacting (from experiment) 2.4g 7.1gmolar mass (look up relative atomic 24g/mol 35.5g/molmass in periodic table)amounts (amount = mass/molar mass) 2.4g/24g/mol 7.1g/35.5g/mol = 0.1mol 0.2molratio of atoms (divide by smallest) 1 : 2formula MgCl2
Work out formulae of compounds formed when the following react:56g of iron and 32g of sulphur (Fe =56, S =32)2g of hydrogen and 16g of oxygen (H=1, O=16)14g of lithium and 16g of oxygen (Li=7)32g of copper and 8g of oxygen (Cu=64)6.4g of copper and 0.8g of oxygen.
C2.08 Calculating reacting masses using equationsYou can work out ratio of the masses of products and reactants by simply multiplying the number of moles shown in the equation by the formula mass of each substance.
Example 1: What mass of magnesium oxide can be made from 12g of magnesium? Relative atomic masses are Mg =24, O = 16. equation 2Mg(s) + O2(g) --> 2MgO(s) formula 2*24 1(16*2) 2(24+16)masses =48 =32 =80 reacting 48g of Mg forms 80g of MgOmasses 1g of Mg forms 80/48 g of MgO 12g of Mg forms 12*80/48 g of MgO = 20g
Example 2: What mass of magnesium oxide can be made from 12g of magnesium? equation 2Mg(s) + O2(g) --> 2MgO(s) amounts 2 moles 1 mole 2 moles masses 2*24 1{16*2} 2{24+16} =48g =32g =80g so 48g Mg forms 80g MgO 1g Mg forms 80/48 g MgO 12g Mg forms 12*80/48 g MgO = 20g Also note that the ratio of amounts of reactants and products in the equation above can be written as:
Amount of Mg/amount of O2 =2/1 Or Amount of O2/amount of MgO = 1/2
problem
You decide to travel from London to Delhi for a holiday and hire your own Airbus 319 jet. You fly the 2183 miles to Cairo first and make 9.4 tons of carbon dioxide. After seeing the Pryramids you fly the 1018 miles to Riyadh making 4.5 tons of carbon dioxide. After a brief stop in the Saudi Capital you fly on the 1900 miles to Delhi making 8.1 tons of carbon dioxide. Finally you return to London travelling 4171 miles and releasing 22 tons of carbon dioxide. The jet burns the fuel kerosine C15H32 in the reaction
C15H32 + 23O2 --> 15CO2 +16H2O(a)
How much carbon dioxide was released into the atmosphere during the trip?(b) What mass of kerosine was burnt?(c) What effect does the trip have of the environment?

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