Ii.
if there are 19 grams of oxygen in a sample of aluminum oxide( a1203).
how many grams of al are present?
iii.
if there are 42 grams of hydrogen in a sample of pure methane (ch4). how many grams of
carbon are present?

Mass of aluminium = 21.59 g

Mass of carbon = 124.98 g

Explanation:

Part ii

Given data:

Mass of oxygen = 19 g

Mass of aluminium = ?

Solution:

Chemical equation:

4Al + 3O₂  →    2Al₂O₃

Now we will calculate the moles of oxygen.

Number of moles = mass / molar mass

Number of moles = 19 g/ 32 g/mol

Number of moles = 0.594 mol

Now we will compare the moles of oxygen and aluminium from balanced chemical equation,

         O₂     :       Al

          3      :        4

     0.594   :        4/3×0.594 = 0.8 mol

Mass of aluminium = moles × molar mass

Mass of aluminium = 0.8 mol  × 26.982 g/mol = 21.59 g

Part iii

Given data:

Mass of hydrogen = 42 g

Mass of carbon = ?

Chemical equation:

C  +  2H₂      →   CH₄

Now we will calculate the moles of hydrogen.

Number of moles = mass / molar mass

Number of moles = 42 g/ 2.016 g/mol

Number of moles = 20.83 mol

Now we will compare the moles of hydrogen and carbon from balanced chemical equation,

          H₂   :       C

          2      :        1

     20.83   :        1/2 ×20.83 = 10.415 mol

Mass of carbon = moles × molar mass

Mass of carbon = 10.415 mol ×12 g/mol = 124.98 g

idk what the question is about