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Formulas and equations

Learn how to write chemical formulas, balance equations, use compound ions, and calculate mole quantities in chemistry. Practice problems included with detailed explanations.

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Formulas and equations

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  1. Sunday, 08 October 2017 Formulas and equations Starter:

  2. Common ions Knowing the charge on ions helps us make chemical formulas Groups 1, 2 and 3 give 1+, 2+ and 3+ ions respectively. Groups 5, 6 and 7 give 3-, 2- and 1- ions respectively. Other important ions include: H+ NO3- Cu2+ NH4+ CO32- Fe2+ SO42- OH- Fe3+ Zn2+ Ag+

  3. Writing ionic formulas: • Na+ and Cl- • Ba2+ and Cl- • Mg2+ and O2- • Al3+ and I- • Sodium and bromine • Zinc and sulfure • Extension: Write 5 more of your own

  4. Writing ionic formulas: Copper chloride Calcium oxide Silver bromide Sodium oxide Iron (II) oxide Iron (III) oxide Extension: Write 5 more of your own

  5. Using compound ions What is a compound ion? An ion that has more than one element Lithium hydroxide Ammonium chloride Copper sulphate Magnesium nitrate Zinc carbonate Ammonium sulphate

  6. Chemical formulas for non-metal elements Most elements exist as just their formula from the periodic table. This includes metals, carbon and group 0 elements. Some non-metals exist as diatomic molecules. Can you name them and write their formulas? HOFBrINCl

  7. Writing balanced equations Li + Cl2 LiCl Na2CO3 + HCl NaCl + H2O + CO2 CH4 + O2  CO2 + H2O K + H2O  KOH + H2 Magnesium + water  magnesium hydroxide + hydrogen

  8. State symbols (s) – solid – most metals, carbon, sulfur, iodine, ionic compounds (l) – liquid – water, bromine, mercury and when solids are melted (g) – gas – most non-metal elements and compounds (aq) – aqueous – dissolved in solution (typically water) e.g. acids, ionic compounds in water

  9. Writing balanced equations Magnesium nitrate undergoes thermal decomposition to produce magnesium oxide, nitrogen dioxide and oxygen. Write a balanced symbol equation for this reaction including state symbols

  10. Relative atomic mass/Relative molecular mass/Relative formula mass RAM – The mean mass of atoms of an element compared to 1/12th of the mass of a carbon-12 atom RMM – used for molecules of simple covalent compounds RFM –used for giant structures. Sum of the relative atomic masses of all the atoms in the formula of the substance

  11. Using RAM to calculate RFM Extension: Complex salts: CuSO4.5H2O

  12. Moles recap Why use mole? How many molecules of water would there be in 18g of water? 602,300,000,000,000,000,000,000 molecules Or 6.02 x 1023 molecules. This number is the Avogadro constant. This number of molecules or particles is equal to 1 mol

  13. Stoichiometry Look at the following equation: How many moles of magnesium oxide will be made from 1 mol of oxygen? 2Mg(s) + O2(g)  2MgO(s) What about this equation? N2(g) + 3H2(g)  2NH3(g)

  14. Stoichiometry Stoichiometry is using the relationship between the reactants and products in a chemical reaction to be able to work out how much product will be made from given amounts of reactants. … or the ratio between reactants and products.

  15. Practice 50g of calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide. Write a balanced symbol equation for this reaction including state symbols Calculate the number of moles of calcium carbonate used Calculate the expected mass of calcium chloride from this reaction

  16. Percentage yield Either: (Number of actual moles/Expected moles) x 100 (Actual mass/theoretical mass) x 100 Given the previous example, what if only 44g of calcium chloride was made, what would the percentage yield be?

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