Acids and bases

• What is an alkali?


  A soluble base
• Write the formulas for:

  a) Nitric acid

  b) Sulphuric acid

  c) Phosphoric acid

  d) Hydrochloric acid


  a) HNO^3

  b) H^2SO^4

  c) H^3PO^4

  d) HCl
• What kind of acid is an acid that contains carbon?


  If an acid contains carbon, it is an organic acid.

  Organic acids are weak
• What is dissociation?


  Breaking a compound up into its ions
• What is the dissociation equation for sulphuric acid?


  H^2SO^4 (aq) ----> 2H^+ (aq) + SO^4^- (aq)
• What is the dissociation equation for calcium hydroxide?


  Ca(OH)^2 (aq) ---> Ca^2+ (aq) + 2OH^- (aq)
• The higher the concentration of H^+, ......?


  The lower the pH = stronger acid
• When is a dissociation reaction reversible?


  When it only partially disscoiates
• What is the dissociation equation for water?

  
• What is [H^2O] when H^2O is a liquid?


  A constant
• What is the equation for k^w?


  K^w = [H^+][OH^-]
• What is the value of k^w?


  1 x 10^-14 mol^2dm^-6 at standard pressure (100,000 Pa) and standard temperature (298K)
• Can the value of K^w change?


  Yes, if the pressure or temperature changes
• What is pure water always?

  Neutral, no matter what the pH is.
• What is the Bronsted-Lowry definition of an acid?


  All acids produce H^+ ions in solutions.

  Acids are proton donors
• What are bases, in terms of protons?


  Proton acceptors
• Label the acid and bases for the reaction between phosphoric acid and water.

  
• What is the equation for pH?

  
• When can you use the ratios in an equation to figure out the concentration?


  When it is a strong acid or base
• What are the units for pH?


  It doesn't have units
• How can you find the pH of a strong base?

  
• What is the equation to find [H^+] when pH is given?

  
• Why is pure water always neutral?


  The [H^+] = [OH^-] so water is neutral
• What is the difference between strong and weak acids?


  Strong acids completely dissociate in solution, weak acids do not (they only partially dissociate)
• What is K^a?


  K^a = K^c for weak acids
• When can't you calculate the concentration of H^+ ions in the dissociation of an acid using the formula ratio?


  When it is a weak acid
• How do you calculate the pH of a weak acid?


  A = anion

  We assume the concentration of HA doesn't change because it only dissociates a little.

  We are given the value of K^a.

  If H^+ and A^- are in a 1:1 ratio, you call them both 1x

  so, k^a = x^2/[HA]

  You can work out x using this and as x = [H^+], you can then work out pH.

  
• Calculate the pH of the solution formed when 20cm^3 of 0.1M HNO^3 is added to 30cm^3 of 0.05M KOH

  
  

  HNO^3 + KOH ---> KNO^3 + H^2O

  Moles of HNO^3: n = CV

  n = 0.1 x (20/1000)

  n = 2 x 10^-3

  Moles of KOH:

  n = 0.05 x (30/1000)

  n = 1.5 x 10^-3

  Excess moles = HNO^3

  (2 x 10^-3) - (1.5 x 10^-3) = 5 x 10^-4

  C = n/V

  C = (5 x 10^-4)/ (50/1000)

  C = 0.01 M

  pH = -log(0.01)

  pH = 2
• Draw a pH curve

  
• What is the equivalence volume and where is it located on the graph?


  Located roughly half way up vertical line

  Equivalence volume (E) is when the acid and base have exactly neutralised each other
• What is the end point?

  When the indicator changes colour (this is most likely inaccurate on when the acid and base have exactly neutralised each other)
• What is the equivalence volume also called?


  Neutralisation volume
• How do you find pKa on a pH graph?


  Read on y-axis

  About half way between 0 and E
• What is W and how is it found on a pH graph?

  Half-neutralisation volume

  Read on x-axis

  About half way between 0 and E
• What are the combinations of acids and bases and their graphs?


  Strong acid and strong base

  Strong acid and weak base

  Weak acid and strong base

  Weak acid and weak base (no real vertical part on graph, more slanted)

  
• What is the equation for pKa?

  
• What does a lower value of pKa indicate?


  The lower the value of pKa, the stronger the acid.
• What is a buffer solution?


  Buffer solutions maintain a constant pH even after a small addition of an alkali or acid
• What are the 2 types of buffer solutions and what range are their pH's usually in?


  1) Acidic buffer

  pH = 2 - 6.5

  2) Basic buffer

  pH = 7 and above
• How do you make an acidic buffer?


  Made by mixing a weak acid and a strong base