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Recap – Formula and bonding

Recap – Formula and bonding. HO. H 2 O 2. Types of bonding : ionic, covalent, metallic Types of formula : empirical, molecular, structural Type of covalent materials : molecular, network. Polarity of Water. The O-H bonds in water are polar.

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Recap – Formula and bonding

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  1. Recap – Formula and bonding HO H2O2 Types of bonding: ionic, covalent, metallic Types of formula: empirical, molecular, structural Type of covalent materials: molecular, network

  2. Polarity of Water • The O-H bonds in water are polar. • The angular shape of the molecule mean water is a ‘polar molecule’. Fig. 4.2 Silberberg

  3. Chemical Reactions Chemical reactions occur because: • Products contain less energy than reactants and systems go to lowest energy state, eg burning gas. • Energy supplied to force reactants to products which have higher energy, eg blast furnace.

  4. Chemical Equations • Word Equation hydrogen plus oxygen forms water • Symbolic Equations – use correct formula • H2+ O2H2O • Need to balance equations. Indicate states • 2H2(g) + O2(g)  2H2O(l)

  5. Chemical Equations • Molecular Equation eg H2(g) + I2(g)  2HI(g) C6H12O6(s)  C6H12O6(aq) • Ionic Equations • eg NaCl (s)  Na+(aq) + Cl-(aq) • Pb2+(aq) + 2I-(aq)  PbI2(s) Precipitate

  6. H+ cation is just a ‘bare proton’, no e-. - e- Hydrogen atom H+ Hydrogen ion • In aqueous solution, H+ associates with H2O to give H3O+(aq), also called H+(aq). O H H + H Reactions with Acid, H+ • Substances that provide H+ ions in water are called ACIDS.

  7. Metal + Acid  Salt + Hydrogen Formula Equation Zn + 2HCl  ZnCl2 + H2 Complete ionic equation Zn(s) + 2H+(aq) + 2Cl-(aq)  Zn2+(aq) + H2(g) + 2Cl-(aq) Net ionic equation Zn(s) + 2H+(aq)  Zn2+(aq) + H2(g) We can isolate the salt by evaporation of the solvent Zn2+(aq) + 2Cl-(aq) ZnCl2(s)

  8. Carbonate + Acid  Salt + H2O + CO2 Formula Equation CaCO3 + 2HCl  CaCl2+ H2O + CO2 Complete ionic equation CaCO3(s) +2H+(aq) + 2Cl-(aq)  Ca2+(aq) + H2O(l) + CO2(g) + 2Cl-(aq) Net ionic equation CaCO3(s) + 2H+(aq) Ca2+(aq) + H2O(l) + CO2(g) We can isolate the salt by evaporation of the solvent Ca2+(aq) + 2Cl-(aq) CaCl2(s)

  9. Learning Outcomes: By the end of this lecture, you should: understand the reason that water dissolves some ionic materials know the component parts of a chemical equation be able to balance a chemical equation recognise a molecular equation, formula equation and an ionic equation be able to describe a chemical reaction in terms of a chemical equation understand an acid supplies H+ ions and exists in water recognise reactions involving dissolution, precipitation and acids be able to complete the worksheet (if you haven’t already done so…)

  10. Questions to complete for next lecture: • Balance the following chemical equations: • CH4(g) + O2(g)  CO2(g) + H2O(l) • CaCl2 + AgNO3  Ca(NO3)2 + AgCl • Ag+(aq) + CrO42-(aq)  Ag2CrO4(s) • Ca(s) + H+(aq)  Ca2+(aq) + H2(g) • Mg(OH)2(s) + H+(aq)  Mg2+(aq) + H2O(l) • Classify the above equations as ‘molecular’, ‘formula’, or ‘net ionic’. • Which of the equations in question 1 represent a precipitation reaction? • Which of the equations in question 1 represent a reaction with acid? • Would it matter if you used hydrochloric acid or sulfuric acid to perform the reaction represented by equation 1d?

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