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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- 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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- 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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