Foundations in Chemistry

• Relative atomic mass


  The weighted mean mass of an atom of an element compared with 1/12th of the mass of an atom of carbon-12
• Relative Isotopic Mass


  The mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12
• Define amount of substance

  Number of particles in a substance, measured in moles
• Define Avogadro's constant


  The number of particle per mole

  
• Mole equation

  
• Number of particles/atoms/electrons equation

  
• Molecular formula


  Number of atoms of each element in a molecule

  
• Empirical formula


  The simplest whole-number ratio of atoms of each element present in a compound

  
• Define anhydrous


  Without water
• Define hydrated


  Crystalline compound containing water molecules
• Equation linking mole and volume

  
• Molar gas volume equation

  
• Ideal Gas Equation

  
• cm3 --> dm3 --> m3

  
• C --> K


  + 273
• Finding the Mr of an unknown metal - Practical

  Set up apparatus:

  Set the conical flask and 250 cm3 measuring cylinder in place and add delivery bung running from the conical flask to measuring cylinder

  Using a measuring cylinder, add the aqueous solution of acid (in excess) to the conical flask.

  Weigh the metal accurately and record the mass

  Remove the stopper and add the metal to the flask and quickly place the stopper on again

  Collect the gas and record the final volume of hydrogen
• Percentage Yield

  
• Atom Economy

  
• Benefits of sustainability - atom economy

  Reactions may have large atom economy but poor percentage yields
• Define a strong acid

  Releases all H+ ions and they completely dissociate
• Define weak acid


  Release a small proportion of H+ ions and they partially dissociate
• acid + metal oxide/hydroxide --> salt + water
• acid + alkali --> salt + water
• Titrations


  Used to determine:

  Concentration of a solution

  Identifying unknown chemicals

  Finding the purity of a substance
• What is a standard solution?

  A solution of known concentration
• How to prepare a standard solution?

  Weigh the solid accurately in a weighing boat using an accurate top-hand balance and transfer the solid into a beaker

  Dissolve the solid in a beaker using distilled water

  Transfer the solution to the volumetric flask using a funnel

  Wash the last traces of the solution into the flask with distilled water and place a stopper over the flask

  Fill the flask to the graduation line by adding distilled water. As you get closer to the line add the distilled water, dropwise until the bottom of the meniscus lines up exactly with the line

  Invert the solution thoroughly (2-3 times) to ensure the solution is mixed thoroughly
• Preparing a standard solution - EXTRA

  Rinse the weighing boat to make sure that all of the solid is in the beaker

  Swirl solution in beaker/use glass stirring rod

  When transferring solution from beaker to volumetric flask make sure there are no spillages

  Use a dropping pipette when close to the graduation line
• Apparatus needed in acid-base titrations

  Pipette

  Burette
• What does the end point indicate?

  Indicates the volume of one solution has exactly reacted with the volume of the second solution
• Acid-base titrations - Procedure

  Using a pipette and filler, transfer 25.0 cm3 of the solution into a conical flask

  Add the other solution to a burette and record the initial burette reading to the nearest 0.05cm3

  Add 3-4 drops of phenolphthalein indicator in the conical flask

  Titrate the solution in the burette into the solution in the conical flask, swirling the flask. Eventually the indicator changes colour (pink -> colourless). This is the end-point titration

  Record the final burette reading.

  Repeat your titration until you have two consistent (concordant) results within 0.10cm3 from each other
• Potential errors in acid-base titrations


  Do not use the rough titration

  Use a white tile under the conical flask so the colour change can be seen more easily

  Swirl the conical flask while adding the solution from the burette to ensure all of the solution has dissolved
• Why is a rough titration carried out?


  To find the approximate titre
• Mean titre


  Only using two titres that agree within 0.10cm3
• OIL RIG


  Oxidation is loss of electrons

  Reduction is the gain of electrons
• Reducing agent


  Loses electrons and become oxidised
• Oxidising agent


  Gains electrons and becomes reduced
• Oxidation numbers


  Uncombined elements always have an oxidation number of 0

  Ions: The oxidation number is the same as the charge on the ion

  Group 1: +1

  Group 2: +2

  Aluminium: +3

  Hydrogen: +1 (except with a metal > -1)

  Chlorine: -1 (except with F or O)

  Oxygen: -2 (except -1 in peroxides and +2 in OF2)