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All you need to know about Additional Science

All you need to know about Additional Science. Topic 3. 3.1 Mass numbers. Mass number – atomic number = number of neutrons E.g. Sodium 23 – 11 = 12. Isotopes Same number of protons Different number of neutrons. 3.2 Masses of atoms and moles. Relative atomic masses (A r )

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All you need to know about Additional Science

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  1. All you need to know about Additional Science Topic 3

  2. 3.1 Mass numbers Mass number – atomic number = number of neutrons E.g. Sodium 23 – 11 = 12 Isotopes • Same number of protons • Different number of neutrons

  3. 3.2 Masses of atoms and moles Relative atomic masses (Ar) Mass of atom compared to 12C e.g. Na = 23, Cl = 35.5 Relative formula masses (Mr) Mass of a compound found by adding Ar of each element e.g. NaCl = 23 + 35.5 = 58.5 Moles • A mole of any substance always contains same number of particles - Relative atomic mass in grams - Relative formula mass in grams

  4. 3.3 Percentages and formulae Percentage mass % = mass of element total mass of compound Percentage composition / empirical formula

  5. 3.4 Balancing equations H2 + O2 H2O

  6. 3.4 Reacting masses 2NaOH + Cl2 NaOCl + NaCl + H2O If we have a solution containing 100 g of sodium hydroxide, how much chlorine gas should we pass through the solution to make bleach? Too much, and some chlorine will be wasted, too little and not all of the sodium hydroxide will react.

  7. 3.4 Reacting masses 2NaOH + Cl2 NaOCl + NaCl + H2O 100 g ?

  8. 3.5 Percentage yield Very few chemical reactions have a yield of 100% because: • Reaction is reversible • Some reactants produce unexpected products • Some products are left behind in apparatus • Reactants may not be completely pure • More than one product is produced and it may be difficult to separate the product we want

  9. 3.5 Percentage yield Percentage yield % yield = amount of product produced (g) x 100% max. amount of product possible (g)

  10. 3.5 Atom economy The amount of the starting materials that end up as useful products is called the atom economy % atom economy = Mr of useful product x 100% Mr of all products

  11. 3.6 Reversible reactions A + B C + D = reversible reaction e.g. iodine monochloride and chlorine gas: ICl + Cl2 ICl3 • increasing Cl2 increases ICl3 • decreasing Cl2 decreases ICl3

  12. 3.7 Haber process • Fritz Haber invented the Haber process • A way of turning nitrogen in the air into ammonia N2 + 3H2 2NH3 450oC 200 atm

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