3.1.2 Amount of substances

• What is the focus of the A level chemistry video mentioned?

  The video focuses on empirical and molecular formulas.
• What is an empirical formula?


  The empirical formula is the simplest whole number ratio of atoms of each element in a compound.
• How does a molecular formula differ from an empirical formula?

  The molecular formula is the actual number of atoms of each element in a compound.
• What is the relationship between empirical and molecular formulas?

  The empirical formula may be a reduced version of the molecular formula.
• If the molecular formula is $C_2H_4$, what is the empirical formula?


  The empirical formula is $CH_2$.
• How do you simplify the ratio of carbon to hydrogen in the molecular formula $C_2H_4$?


  You simplify the ratio from 2:4 to 1:2.
• What is the empirical formula for a compound with a molecular formula of $C_4H_8O_6$?


  The empirical formula is $C_2H_4O_3$.
• What is the empirical formula of magnesium oxide determined through an experiment?

  The empirical formula of magnesium oxide is $MgO$.
• What is the definition of water of crystallization?

  Water of crystallization refers to water molecules that are part of the crystalline structure of a compound.
• How do you determine the value for the water of crystallization in an experiment?

  You determine it by measuring the mass loss upon heating the hydrated compound.
• What is the empirical formula of a compound with a molecular formula of $C_6H_{12}O_6$?


  The empirical formula is $C_1H_2O_1$.
• How do you calculate the empirical formula from mass data?

  You calculate it by determining the moles of each element and finding the simplest ratio.
• In the example with 1.2 grams of carbon and 0.4 grams of hydrogen, what is the empirical formula?

  The empirical formula is <latex{CH_4}</latex>.
• How do you find the mass of oxygen in the phosphorus oxide example?

  You subtract the mass of phosphorus from the total mass of the compound.
• What is the significance of not rounding ratios in empirical formula calculations?

  Not rounding ensures accurate representation of the simplest whole number ratio.
• If a hydrocarbon contains 84.2% carbon, what is the percentage of hydrogen?

  The percentage of hydrogen is 15.8%.
• How do you convert a ratio of 1:2.5 to whole numbers for an empirical formula?

  You multiply both numbers by 2 to get a ratio of 2:5.
• What is the empirical formula of a hydrocarbon with 3.17 grams of carbon and 0.528 grams of hydrogen?

  The empirical formula is <latex{C_6H_{12}}.</latex>
• What is the first step in calculating the molecular formula from the empirical formula?

  The first step is to calculate the mass of the empirical formula.
• If the empirical formula is <latex{C_3H_5O_2}</latex> and the relative molecular mass is 146, what is the molecular formula?

  The molecular formula is <latex{C_6H_{12}O_4}</latex>.
• How do you find the ratio of molecular formula to empirical formula?

  You divide the relative molecular mass by the mass of the empirical formula.
• What is the final molecular formula if the empirical formula is <latex{C_2H_6O}</latex> and the relative molecular mass is 92?

  The final molecular formula is <latex{C_4H_{12}O_2}</latex>.
• In the example with 3.17 grams of carbon and 0.528 grams of hydrogen, what is the first step to find the empirical formula?

  The first step is to list the masses of carbon and hydrogen.
• What is the relative atomic mass of carbon used in the calculations?

  The relative atomic mass of carbon is 12.0.
• What is the relative atomic mass of hydrogen used in the calculations?

  The relative atomic mass of hydrogen is 1.0.
• Why is it important to follow a systematic approach when calculating empirical formulas?

  A systematic approach ensures accuracy and consistency in calculations.
• What is the mass of phosphorus in the example given?

  The mass of phosphorus is 10.7 grams.
• What is the total mass of the phosphorus oxide compound in the example?

  The total mass of the phosphorus oxide compound is 24.5 grams.
• What is the mass of oxygen calculated in the phosphorus oxide example?

  The mass of oxygen is 13.8 grams.
• What is the significance of the relative atomic mass in empirical formula calculations?

  The relative atomic mass is used to convert mass to moles in calculations.
• How do you calculate the moles of an element from its mass and relative atomic mass?

  You divide the mass of the element by its relative atomic mass.
• What is the importance of determining the empirical formula in chemistry?

  The empirical formula provides the simplest ratio of elements in a compound, which is essential for understanding its composition.
• What is the empirical formula of a compound with a 1:4 ratio of carbon to hydrogen?

  The empirical formula is <latex{CH_4}</latex>.
• What is the empirical formula of a compound with a 1:2.5 ratio of phosphorus to oxygen?

  The empirical formula is <latex{P_2O_5}</latex>.
• Why is it necessary to scale ratios in empirical formula calculations?

  Scaling ensures that the ratios are whole numbers, which is required for empirical formulas.
• What is the empirical formula for a hydrocarbon with 84.2% carbon and 15.8% hydrogen?

  The empirical formula is <latex{C_4H_9}</latex>.
• How do you determine the molecular formula from the empirical formula?

  You determine it by finding the ratio of the molecular mass to the empirical formula mass.
• What is the relative molecular mass of the compound with the empirical formula <latex{C_3H_5O_2}</latex>?

  The relative molecular mass is 146.
• If the empirical formula is <latex{C_2H_6O}</latex> and the relative molecular mass is 92, what is the molecular formula?

  The molecular formula is <latex{C_4H_{12}O_2}</latex>.
• How do you calculate the mass of the empirical formula for <latex{C_2H_6O}</latex>?

  The mass is calculated as <latex{24 + 6 + 16 = 46}</latex>.