Acids and Redox

• What do acids release when dissolved in water?

  Hydrogen ions e.g HCl + aq --> H+ + Cl-
• What is a strong acid?

  releases all hydrogen atoms into solution as hydrogen ions - completely dissociates e.g HCl
• What is a weak acid?

  releases a small portion of its hydrogen atoms into solution as hydrogen ions - partially dissociates e.g ethanoic acid
• What is a base?

  substance which neutralises an acid to form a salt

  alkalis are bases that dissolve in water releasing hydroxide ions
• How do you prepare a standard solution (solution of known conc)?

  Weigh the solid accurately

  Dissolve it in a beaker using less distilled water than needed to fill volumetric flask to the mark

  Solution is transferred to a volumetric flask

  Rinse leftovers with distilled water and pour into flask

  Fill flask to graduation line by adding distilled water drop by drop

  Invert the flask multiple times to mix the solution
• What is the acid-base titration procedure?

  Add measure volume of alkali to flask using a pipette

  Add acid to burette and record initial reading

  Add drops of phenolphthalein to flask - turns pink

  Open burette tap mixing two solutions drop by drop

  Once solution is turning colourless close tap

  Find the titre - final reading - initial

  Carry out trial titration first

  Repeat 3 times until 2 concordant results found - within 0.10 cm3
• What is the titration equation?

  n=cv

  n - moles

  c - concentration in moldm-3

  v - volume in dm3
• What is the oxidation number of diatomic molecules?

  0
• What is the oxidation number for oxygen and group 6 elements when in a compound?

  -2
• What is the oxidation number for hydrogen when in a compound?

  +1
• What is the oxidation number for fluorine and group 7 elements when in a compound?

  -1
• What is the oxidation number for sodium and other group 1 elements when in a compound?

  +1
• What is the oxidation number for magnesium and other group 2 elements when in a compound?

  +2
• What is the oxidation number for hydrogen when in metal anhydrides?

  -1 e.g NaH, CaH2
• What is the oxidation number for oxygen in peroxides?

  -1 e.g H2O2 - hydrogen peroxide
• What is the oxidation number for oxygen when bonded to fluorine?

  +2 e.g F2O
• What is the rule for oxidation numbers of combined atoms?

  sum of oxidation numbers = total charge
• What is oxidation and reduction in terms of oxygen?

  Oxidation - addition of oxygen

  Reduction - removal of oxygen
• What is oxidation and reduction in terms of electrons?

  Oxidation - loss of electrons

  Reduction - gain of electrons
• What is oxidation and reduction in terms of oxidation number?

  Oxidation - increase in oxidation number

  Reduction - decrease in oxidation number