C2 T6 Quantitative Chemistry

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  • Created by: Ghaydaa
  • Created on: 25-12-13 13:22

Relative Atomic Mass

  • RAM (Ar) is the same as the MASS NUMBER (top number, usually the bigger number) of any element.
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Relative Formula Mass

  • The sum of all the relative atomic masses added together...
  • e.g. the Mr of magnesium chloride, MgCl2 would be: Ar of Mg(24) + Ar of Cl (35.5x2) = 95.
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Percentage Composition by Mass of Elements in a Co

  • % mass of an element in a compound = [(Ar x no. of element atoms) / Mr of compound] x100%.
  • e.g. % mass of Na in Na2CO3= 23x2/106 x 100% = 43.4%.
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Empirical Formula

  • List the elements in the compound.
  • Underneath, write down their experimental masses (given in the question).
  • Divide by the Ar of its element.
  • Ratio it by multiplying or dividing.
  • Using the ratio in its simplest form, write the formula of the cmpound.

  • BASICALLY, DIVIDE THE EXPERIMENTAL MASS BY THE Ar OF THE ELEMENT THEN SIMPLIFY INTO A RATIO TO MAKE A FORMULA FROM.
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Masses in Reactions

  • Write out the balanced equation.
  • Work out the relative formula masses for the elements you need.
  • Divide to get 1 unit, then multiply to get the required unit.
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Percentage Yield

  • Percetage yield compares actual yield and theoretical yield.
  • % yield = actual yield (g) / theoretical yield (g) x100%
  • Yield are always less than 100%...
  • Due to: 1. Incomplete reactions; 2. Practical losses during preparation; 3. Unwanted reactions.
  • Waste in reactions costs money, so reactions that make lots of waste aren't usually profitable.
  • Disposing of harmful waste products safely can be very expensive.
  • Chemists in industry are always looking for ways to produce products in a way that makes the most profit safely. 
  • Chemists work to find reactions with these characteristics:
  • a) They give a high % yield, so lots of product is made from th expensive raw materials
  • b) All of the products are comercially useful, depleting waste
  • c) They are at a suitable speed, so products are made quickly and safely.
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