quantitative

• Law of conservation of mass


  No atoms are lost or made during a chemical reaction, so the mass of the products equals the mass of the reactants
• Chemical reaction


  1. Reactants

  2. Products
• In a chemical reaction, the starting materials are called the reactants, and the chemicals that are formed are called the products
• The mass of the products equals the mass of the reactants in a chemical reaction
• Non-metal ions


  Mostly negative
• Charge on ions


  Relates to group in periodic table
• Metal ions


  • Na+
  • Mg2+
  • Al3+
• Charge on metal ions

  Often the same as the group number in periodic table
• Transition metals can form several different ions
• Transition metal ions


  • Fe2+
  • Fe3+
  • Cu+
  • Cu2+
• Non-metal ions


  • O2-
  • F-
• Charge on non-metal ions

  Relates to group in periodic table
• Non-metal ions


  • S2-
  • Cl-
  • Br-
• Ionic compound


  The charges on the ions have to cancel out to leave an overall charge of zero
• Some non-metal ions consist of several non-metal atoms chemically combined
• Hydrogen ion (H+) and ammonium ion (NH4+) are positive non-metal ions
• Ionic compounds


  • Have no overall charge
• Ionic compounds


  • Na2SO4
  • Ca(OH)2
• Determining the formula of an ionic compound

  1. Identify the charges on the ions

  2. Determine the number of each ion needed to cancel out the charges

  3. Write the formula using the appropriate number of each ion
• Chemical formula


  Shows the formula of a compound, with capital letters indicating elements and small numbers indicating the number of atoms of each element
• Large numbers in front of a chemical formula indicate multiple molecules of that compound
• Balancing a chemical equation

  1. Count the number of atoms of each element on the left and right sides

  2. Ensure the number of atoms of each element is the same on both sides

  3. Use large numbers in front of compounds to balance the equation
• Steps to balance the unbalanced equation

  1. Count the number of atoms of each element on the left and right sides

  2. Place a large number in front of the compound on the right side to balance the iodine atoms

  3. Place a large number in front of the compound on the left side to balance the sodium atoms
• Relative formula mass


  The sum of the relative atomic masses of the atoms in the numbers shown in the formula
• Relative formula mass has no units
• Relative formula mass never involves big numbers
• Relative atomic mass


  The average mass of the isotopes of an element weighted to take into account the abundance of each isotope
• Chlorine has two main isotopes with mass numbers 35 and 37
• The relative atomic mass of chlorine is 35.5 due to the weighted average of the two isotopes
• Calculating relative formula mass


  Sum the relative atomic masses of the atoms in the numbers shown in the formula
• Relative formula mass calculations

  • Methane (CH4): 1 x 12 + 4 x 1 = 16
  • Calcium sulfate (CaSO4): 1 x 40 + 1 x 32 + 4 x 16 = 136
  • Magnesium hydroxide (Mg(OH)2): 1 x 24 + 2 x 16 + 2 x 1 = 58
• Percentage by mass


  Percentage of the relative formula mass that is due to one of the elements in a compound
• Calculating percentage by mass


  Total relative atomic mass of the atoms of that element / Relative formula mass of the compound x 100
• Relative formula mass


  Mass of the compound calculated by adding together the relative atomic masses of the atoms in the numbers shown in the formula
• Percentage by mass should be given to the nearest whole number, except for the final example which should be given to one decimal place
• Mole


  A very large number that scientists use as a shorthand way to represent the number of atoms in a substance
• The relative atomic mass of carbon is 12
• The relative atomic mass of oxygen is 16
• Relative atomic mass


  The mass of a single atom of an element, calculated from the average masses of the isotopes weighted for their abundance
• Calculating the number of moles

  Mass of element in grams / Relative atomic mass = Number of moles