Topic 1.3 chemical reactions and related calculationsPresentation Transcript
Topic 1.3 Chemical reactions and related calculations file://localhost/Users/carter.j/Movies/iSkysoft Free Video Downloader Videos/Chemistry - A Volatile History (Episode 1)(Part 2-6).flv
Topic 1.3: Chemical reactions and related calculations When elements react, their atoms join with other atoms to form compounds
The reaction of Iron and Sulfur Fe + S FeS 11/8/2011
Relative formula mass (Mr) The relative formula mass is the sum of the masses The decimal points are really important, if it is of the atoms in 1.0 on the the numbers shown in the formula. periodic table then that is thenumber you use, and you mustquote your answer to the same number of decimal places! E.g. The relative atomic mass (Ar) of Hydrogen is 1.0 There are two hydrogen atoms in a molecule of H2 so the Mr of H2 is 1.0 + 1.0 = 2.0
From yesterday’s practical Iron reacts with sulfur to form iron sulfide with a formula of FeS Fe has an Ar of 55.8 S has an Ar of 32.1 Therefore the Mr of FeS is 55.8 + 32.1 =
Calculate the relative formula mass (Mr) of: A) Cl2 G) Ca(OH)2 B) Ne H) K2SO4 C) NH3 I) NH4NO3 D) CH4 J) Ca(NO3)2 E) MgBr2 K) Al2(SO4)3 F) S8 L) H2C2O4.2H2O
Calculate the relative formula mass (Mr) of: A) Cl2 71.0 G) Ca(OH)2 74.1 B) Ne 20.2 H) K2SO4 174.3 C) NH3 15.0 I) NH4NO3 D) CH4 16.0 80 E) MgBr2 184.1 J) Ca(NO3)2 164.1 F) S8 256.8 K) Al2(SO4)3 342.3 L) H2C2O4.2H2O 126
The reaction of Magnesium and Oxygen
Avogadro’s number & the mole A mole is the amount of a substance in grams which has the same number of particles as there are atoms in 12 g of 12C. Italian physicist Amedeo Avogadro was investigating the number of molecules in different volumes of gases, and found that, under the same conditions, one mole of a gas always contained the same number of particles. So, one mole of CO2 has the same number of particles as one mole of helium or one mole of methane, or any other gas. The symbol for the Avogadro constant is L after the Austrian Loschmidt, who originally calculated the value for the constant, which is 6.023 x 1023, (602,300,000,000,000,000,000,000,000). You do not need to learn this!
The Avogadro constant is given the symbol L. L = 6.023 x 1023 particles mol-1 The mole is a quantity of particles. 1 mol is 6.023 x 1023 particles The mass of a 12C atom is 1.992 x 10-23 g. If a mole contains 6.023 x 1023 of these atoms, then a mole of 12C has a mass of: 6.023 x 1023 x 1.992 x 10-23 = 11.998 g Avogadro’s number is the number of atoms in 12 g of carbon You do not need to learn this!
The relative formula mass of a substance, in grams, is known as one mole of that substance Candidates are expected to use the relative formula mass of a substance to calculate the number of moles in a given mass of that substance and vice versa.
Moles and masses: To convert the mass of a substance to moles use: Number of moles of an element = mass Ar Number of moles of a compound = mass Mr
Balanced equations Chemical reactions can be represented by word equations or symbol equations. Candidates should be able to write word and balanced symbol equations for reactions in the specification.
Some common anion names: F FluorideMake a copy of this Cl Chloridetable in your book! I Iodide Br Bromide O Oxide OH Hydroxide CO3 Carbonate SO4 Sulfate NO3/NO2 Nitrate PO4 Phosphate The –ate at the end of some anion names means that they contain oxygen, eg sulfate contains sulfur and oxygen, sulfide is just sulfur on its own.
Balancing equations - 1 From the worksheet, first try to balance the equation, then try to write a word equation for the reaction E.g. H2 + Cl2 HCl H2 + Cl2 2HCl Balanced Hydrogen + Chlorine Hydrogen chloride
States: (s), (l), (g), (aq)
In a chemical equation the states are shown for the elements of compound at room temperature. E.g. Sodium + water sodium hydroxide + hydrogen 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)It tells us that solid sodium reacts with liquid water toproduce a solution of sodium hydroxide and hydrogen gas
Homework Complete worksheet: Equations and Molar Ratios
Percentage mass The percentage mass of an element in a formula can be calculated by dividing the the relative mass of the compound by the relative atomic mass of the element in the formula: E.g. The percentage mass of H in CH4 There are 4 x 1.0 = 4.0 4.0/16.0 = 0.25 or 25%
Calculate the percentage mass in the following a) C in CH4 e) N in Ca(NO3)2 b) Br in MgBr2 f) O in Ca(NO3)2 c) S in K2SO4 g) O in Ca(OH)2 d) N in NH4NO3 h) O in Fe(NO3)3
Calculate the percentage mass in the following a) C in CH4 e) N in Ca(NO3)2 75.0% 17.1% b) Br in MgBr2 f) O in Ca(NO3)2 86.8% 58.5`% c) S in K2SO4 g) O in Ca(OH)2 18.4% 43.2% d) N in NH4NO3 h) O in Fe(NO3)3 35.0% 59.6%
Find the % of C in CO2 27.3%Find the % of H in H2O 11.1%Find the % of Zn in ZnCO3 52.2%Find the % of Mg in MgCl2 25.3%Find the % of Pb in PbO2 86.6%Find the % of Cl in MgCl2 74.7%Find the % of Pb in Pb2O3 89.6%
Calculating reacting masses The masses of reactants and products can be calculated from balanced symbol equations Candidates should be able to calculate the mass of a reactant or product from information about the mass of the other reactants and products in the reaction and the balanced symbol equation
The reaction of a iodine with zinc Intention – to carry out a reaction that will allow us to apply all the skills we have been learning this week (balancing equations, calculating Mr values and working out numbers of moles) Take photos of each stage, you will need them to produce a flow diagram of the investigation.
Mole calculations 1. Calculate the number of moles that you have using the mass you are given in the question and the Mr Mass Number of moles of ______ = _____ / _____ = ____Moles Mr Find the ratio (stoichiometry) of the reaction equation If I have ____ moles of _____, then I must have ____ moles of _____. Find the mass of the unknown: Mass of _____ = moles x Mr = _____ x _____ = ______g
Finding the value of X in CuSO4.XH2O Intention – to carry out a reaction that will allow us to further develop all the skills we have been learning (balancing equations, calculating Mr values and working out numbers of moles)
Irreversible reactions The combustion of methane (CH4) to make CO2 and H2O is an irreversible reaction: CH4 + 2O2 CO2 + 2H2O What this means is that we cannot react CO2 and H2O together to make CH4 and O2 CO2 + 2H2O CH4 + 2O2
Reversible reactions A reversible reaction is a chemical change in which the products can be converted back to the reactants under suitable conditions. A reversible reaction can be shown by the sign
Revision materialsTask, in pairs, produce revision material(s) on one of thefollowing topics: Balancing equations The mole Relative molecular mass Conservation of mass in a reaction Yield Reversible reactions
Key words Clear explanations Colourful andUse diagrams Revision materials attractive to look at Include model Include test answers questions