2.3 - Calculations
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Relative Formula Mass
The sum of the atomic masses in each element
What is the relative atomic mass of Ammonium Carbonate (NH4)2 CO3 Nitrogen = 14 Hydrogen = 1 Carbon = 12 Oxygen = 16
N = 14x2=28 H = 1x8=8 C = 12x1=12 O = 16x3=48 28+8+12+48 =96g/mole
What is the measurement of Relative Formula Mass
g/mole
What is the link between moles and RFM
1 mole of a substance is equal to its RFM
What is the formula for percentage by mass
Total mass of element in a compound Divided by It’s RFM
Empirical Formula is…
Divide the percentage or mass given by it’s relative atomic mass number Then Divide your answers by the smallest answer Aim to get whole numbers
Predicting masses you…
Look for ratios i.e what something has been times or divided by and do the same to the other Or Use the RFM’s if only one set of data is given
How to workout the moles of a substance?
Moles = Mass / RFM
How to work out Percentage Yield?
Actual mass / Predicted mass All x100
Why do we not always get exactly what we predicted for the mass?
The reaction may not all complete Some products may be lost when separated or collected Reactants can react differently to how expected
Why do you want a high yield in industry?
Conserve resources and reduces waste
What is a reversible reaction?
If the products can react to products then products then the reaction can go in both directions
Example of a reversible reaction?
Ammonium Chloride + Hydrogen Chloride
What are substances added to food called to improve qualities?
Food additives (natural or synthetic)
What can foods be checked by to make sure they are safe additives?
Chemical analysis: Gas chromatography
What does chromatography of food allow?
Allows dyes in foods to separate
The least soluble dye in chromatography…
Travels the least distance
The most soluable dye in chromatography…
Travels the furthest distance