Chemistry calculations

• What is an empirical formula?

  The simplest whole number ratio of atoms
• What does the law of conservation of mass state?

  Mass is conserved in closed systems
• What is the smallest part of an element that can exist?

  An atom
• How is mass measured?

  In kilograms (kg) or grams (g)
• What is relative atomic mass?

  The mean relative mass of isotopes
• How is the relative atomic mass of an element defined?

  Compared to one-twelfth of a carbon-12 atom
• What is the symbol for relative atomic mass?

  A_r
• What does a relative atomic mass of 12 for carbon indicate?

  Carbon atoms are 12 times heavier than carbon-12
• How do relative atomic masses of elements relate to each other?

  They are proportional measures of atomic mass
• What is relative formula mass?

  The sum of relative atomic masses in a formula
• What is the symbol for relative formula mass?

  M_r
• How do you calculate the relative formula mass of a substance?

  Add the relative atomic masses of its atoms
• How is the relative formula mass of carbon dioxide calculated?

  M_r = 12 + 16 + 16 = 44
• What does the relative formula mass of ionic compounds represent?

  It is calculated similarly to molecular compounds
• What is an ionic compound?

  Formed from positive and negative ions
• How do you calculate the relative formula mass of calcium hydroxide, Ca(OH)₂?

  M_r = 40 + (2 × 16) + (2 × 1) = 74
• What is the relative atomic mass of calcium?

  40
• What is the relative atomic mass of oxygen?

  16
• What is the relative atomic mass of hydrogen?

  1
• What are the steps to calculate relative formula mass?

  1. Identify the number of atoms of each element.
  2. Find the relative atomic masses of each element.
  3. Sum the products of the number of atoms and their relative atomic masses.
• What is the relationship between relative atomic mass and the periodic table?

  • Relative atomic masses are listed in the periodic table.
  • They help in calculating relative formula mass.
  • They indicate the mass of an atom compared to carbon-12.
• What are the differences between ionic compounds and molecular compounds?

  • Ionic compounds consist of ions.
  • Molecular compounds consist of molecules.
  • Ionic compounds do not exist as discrete molecules.
• What is an empirical formula?

  A formula showing the simplest ratio of elements
• How is the empirical formula of a substance determined?

  Using masses and relative atomic masses of elements
• What does the law of conservation of mass state?

  Mass is conserved in closed systems
• What is the formula to find the percentage of an element in a compound?

  \({\%~of~an~element} = \frac{mass~of~an~element~in~the~compound}{relative~formula~mass~M_r} \times 100\)
• How do you calculate the percentage by mass of hydrogen in ethanol C₂H₅OH?

  \({\%~of~hydrogen} = \frac{6}{46} \times 100 = 13\%\)
• What is the relative formula mass (M_r) of ethanol C₂H₅OH?

  46
• What is the mass of hydrogen in ethanol C₂H₅OH?

  6
• Why do chemists use moles?

  To count particles in a substance
• How many particles are in one mole?

  6 × 10²³
• What is the mass of one mole of carbon?

  12 g
• What is the relative formula mass of water?

  18
• How much does one mole of water weigh?

  18 grams
• What does one mole of water contain?

  6 × 10²³ molecules
• What is the process to find the percentage of an element in a compound?

  1. Calculate the relative formula mass (M_r) of the compound.
  2. Determine the mass of the element in the compound.
  3. Use the formula:

  \({\%~of~an~element} = \frac{mass~of~an~element~in~the~compound}{relative~formula~mass~M_r} \times 100\)
• What are the key concepts related to moles in chemistry?

  • A mole measures the amount of substance.
  • Contains \(6 \times 10^{23}\) particles.
  • Mass of one mole equals its relative formula mass.
• What is the empirical formula of a substance?

  The simplest whole number ratio of atoms
• How is the empirical formula of a substance determined?

  Using masses and relative atomic masses
• What does the law of conservation of mass state?

  Mass is conserved in closed systems