Percentages and Formula

Descripción

GCSE (How much?) Chemistry Mapa Mental sobre Percentages and Formula, creado por emilywebber98 el 26/11/2013.
emilywebber98
Mapa Mental por emilywebber98, actualizado hace más de 1 año
emilywebber98
Creado por emilywebber98 hace más de 10 años
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Resumen del Recurso

Percentages and Formula
  1. Percentage Composition
    1. use the RAMs of the elements in the compounds and it's formula to work this out
      1. EXAMPLE QUESTION: find the percentage of magnesium in magnesium oxide?
        1. Step 1: find the formula of the compound (MgO) and then find the relative formula mass of the elements and then the compound ( Mg = 24 O= 16, 24 + 16 = 40)
          1. Step 2 : So 24g in 40g of MgO is Mg so you need to find the fraction of this i.e. mass of element/mass of compound
            1. Step 3: To finish it all of you need to find the percentage (24/40 x 100= 60%)
          2. Empirical Formula
            1. Step 1: change the percentages given to masses of each element in 100g of the compound
              1. 75 % Carbon and 25% Hydrogen = 75g Carbon and 25g Hydrogen
              2. Step 2: Change the masses to moles of atoms by dividing the masses by Ar values
                1. This tells you the ratio of atoms of the different elements in the compound
                  1. For carbon: 75/12 = 6.25 moles, For Hydrogen: 25/1 = 25 moles
                  2. Step 3: Then the simplest whole numbers ratio gives you the empirical formula of the compound
                    1. 6.25:25 = 1:4 so the formula is CH4
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