# 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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