Quantitative chemistry

• What is the topic covered in today's video?

  Relative formula mass and related calculations
• Where can you find the mass number of an element?


  In the top left corner of its nuclear symbol
• What does the mass number represent?


  The number of protons plus the number of neutrons in the nucleus
• What is relative atomic mass denoted by?


  It is denoted by $Ar$
• What is the relative atomic mass of chlorine?


  35.5
• How is the relative atomic mass of an element calculated?


  It is the average mass of all the isotopes of that element
• What is relative formula mass denoted by?


  It is denoted by $Mr$
• How do you find the relative formula mass of a compound?


  Add together the relative atomic masses of all the atoms in its molecular formula
• What is the relative formula mass of magnesium chloride (MgCl₂)?


  95
• What is the calculation for the relative formula mass of sulfuric acid (H₂SO₄)?


  2 times 1 plus 1 times 32 plus 4 times 16 equals 98
• How do you calculate the percentage mass of an element in a compound?


  Use the formula: $\frac{(Ar \text{ of element}) \times (\text{number of atoms})}{Mr \text{ of compound}} \times 100$
• What is the percentage mass of sulfur in sulfuric acid?


  32.7%
• What is the first step to find the percentage mass of oxygen in calcium hydroxide (Ca(OH)₂)?


  Recall the relative atomic mass of each element
• What is the relative atomic mass of calcium, oxygen, and hydrogen?


  40 for calcium, 16 for oxygen, and 1 for hydrogen
• How do you calculate the percentage mass of oxygen in calcium hydroxide?


  Calculate $\frac{32}{74} \times 100 =$$43.2\%$
• What are the steps to calculate the relative formula mass of a compound?


  1. Identify the molecular formula of the compound.
  2. Find the relative atomic masses of each element.
  3. Multiply the relative atomic mass by the number of atoms for each element.
  4. Add all the values together to get the relative formula mass.
• What is the term used to measure the amount of chemical substance?

  Mole
• What is the process to find the percentage mass of an element in a compound?


  1. Identify the relative atomic mass of the element.
  2. Determine the number of atoms of that element in the compound.
  3. Calculate the relative formula mass of the compound.
  4. Use the formula: $\frac{(Ar \text{ of element}) \times (\text{number of atoms})}{Mr \text{ of compound}} \times 100$.
• How is the mole similar to other units of measurement like meters and seconds?


  It measures the amount of substance, just like meters measure distance and seconds measure time.
• How many particles are in one mole of a substance?


  1. 02 times 10 to the 23
• What does the term "particles" refer to in the context of moles?


  Particles can refer to atoms, molecules, ions, or electrons.
• If you have one mole of carbon, how many atoms of carbon do you have?


  1. 02 times 10 to the 23 atoms of carbon
• What is Avogadro's constant?


  Avogadro's constant is the number of particles in one mole, which is 6.02 times 10 to the 23.
• Why is Avogadro's constant significant in chemistry?


  It allows us to relate the mass of a substance to the number of particles it contains.
• What is the relative atomic mass of carbon?


  12
• What is the relative formula mass of oxygen in O2?


  32
• What is the relative formula mass of carbon dioxide (CO2)?


  44
• How do you calculate the number of moles in a sample?


  The number of moles is equal to the mass of the element or compound divided by its relative formula mass (mr).
• What does the term "mole" refer to in chemistry?


  A unit used to measure the amount of chemical substance
• How is the mole similar to other units of measurement like meters and seconds?


  It measures the amount of substance, just like meters measure distance
• How many particles are in one mole of a substance?


  1. 02 times 10 to the 23 particles
• How many moles are in 42.5 grams of ammonia (NH3) if its mr is 17?


  1. 5 moles
• What is the mass of 3 moles of carbon dioxide (CO2)?


  132 grams
• What types of particles can be counted as "particles" in the context of moles?


  Atoms, molecules, ions, or electrons
• How do you find the mass of carbon in 3 moles of carbon dioxide?


  Multiply the number of moles (3) by the mass of carbon (12), which gives 36 grams.
• If you have one mole of carbon, how many atoms of carbon do you have?


  1. 02 times 10 to the 23 atoms of carbon
• If you subtract the mass of carbon from the total mass of carbon dioxide, what do you find?


  You find the mass of oxygen in carbon dioxide, which is 96 grams.
• What is Avogadro's constant?


  The number of particles in one mole, which is 6.02 times 10 to the 23
• How can chemical equations be interpreted in terms of moles?


  Chemical equations can be viewed as ratios of moles of reactants and products.
• Why does one mole of a substance weigh the same number of grams as its relative atomic or formula mass?


  Because the mass of that many particles equals the relative atomic or formula mass in grams