Acids and bases

1
Acids and bases
2
Common acids/ bases
3
Acids

• Most acids have the general formula HA, where A-
  is an anion.
• HA ---? H A - in solution.
• In aqueous solutions acids increase the hydrogen
  ion (H) concentration.
• Acids are proton donors H
• Acids are chemical compounds that have a sharp
  taste, a corrosive action on metals, and turn
  blue Litmus paper red.

4
Properties of Acids

• taste sour (don't taste them!)... the word 'acid'
  comes from the Latin acere, which means 'sour'
• acids change litmus (a blue vegetable dye) from
  blue to red
• their aqueous (water) solutions conduct electric
  current (are electrolytes)
• react with bases to form salts and water
• evolve hydrogen gas (H2) upon reaction with an
  active metal (such as alkali metals, alkaline
  earth metals, zinc, aluminum)

5
Examples of Common Acids

• citric acid (from certain fruits and veggies,
  notably citrus fruits)
• ascorbic acid (vitamin C, as from certain fruits)
  
• vinegar (5 acetic acid)
• carbonic acid (for carbonation of soft drinks)
• lactic acid (in buttermilk

6
Acid proton donor
7
Bases

• Most bases have the form BOH, where B is an
  appropriate cation.
• BOH --? B OH- in solution
• Bases are proton acceptors H
• H OH- ----? H2O
• Bases are chemical compounds that, in solution,
  are soapy to the touch and turn red vegetable
  dyes blue.

8
Properties of Bases

• taste bitter (don't taste them!)
• feel slippery or soapy (don't arbitrarily touch
  them!)
• bases don't change the color of litmus they can
  turn red (acidified) litmus back to blue
• their aqueous (water) solutions conduct and
  electric current (are electrolytes)
• react with acids to form salts and water

9
Examples of Common Bases

• detergents
• soap
• lye (NaOH)
• household ammonia (aqueous)

10
Examples of acids and bases
11
Acid base reactions

• Greek words meaning "acid" (from the Greek ????
  (oxys) meaning "acid
• Neutralization reactions
• acid base- ? salt water
• 2NaOH H2SO4 ? 2 H2O Na2SO4

12
Acids and bases neutralize

• Acids and bases can be grouped into two general
  types strong and weak acids and bases.
• When mixed, acids and bases neutralize one
  another and produce salts. These are substances
  with a salty taste and none of the characteristic
  properties of either acids or bases.

13
Acids and bases neutralize

• Acid-base reactions are universal.
• When an acid and a base react in an aqueous
  solution the H and OH- ions combine to form
  water. These ions thus "neutralize" one another.
• HCl NaOH -? NaCl H2O

14
pH scale
15
pH scale
16
pH scale definition

• The pH scale measures how acidic or basic a
  substance is. The pH scale ranges from 0 to 14. A
  pH of 7 is neutral. A pH less than 7 is acidic. A
  pH greater than 7 is basic.
• The pH scale is logarithmic and as a result, each
  whole pH value below 7 is ten times more acidic
  than the next higher value. For example, pH 4 is
  ten times more acidic than pH 5 and 100 times (10
  times 10) more acidic than pH 6.

17
pH scale
18
(No Transcript)
19
pH indicators
20
Indicators
21
Diagram of indicators
22
What is an acid-base indicator?

• An acid-base indicator is a weak acid or a weak
  base.
• The undissociated form of the indicator is a
  different color than the iogenic form of the
  indicator.
• An Indicator changes colour depending on the
  hydrogen ion concentration.

23
Adding hydroxide ions
24
Adding hydrogen ions
25
Methyl orange

You have the same sort of equilibrium between the
two forms of methyl orange as in the litmus case
- but the colours are different.
You have the same sort of equilibrium between the
two forms of methyl orange as in the litmus case
- but the colours are different.
You have the same sort of equilibrium between the
two forms of methyl orange as in the litmus case
- but the colours are different.
You have the same sort of equilibrium between the
two forms of methyl orange as in the litmus case
- but the colours are different.
26
Volumetric analysis
27
Titration experiment

• An acid-base titration is a method in chemistry
  that allows quantitative analysis of the
  concentration of an unknown acid or base
  solution. It makes use of the neutralization
  reaction that occurs between acids and bases and
  the knowledge of how acids and bases will react
  if their formulas are known.

28
Method

• Title To standardize an unknown solution of
  NaOH using a standard solution of HCl.
• Apparatus (Equipment).

29
Apparatus / Equipment

• The key equipment used in a titration are
• Burette
• White Tile - used to see a colour change in the
  solution
• Pipette
• Acid/Base Indicator (the one used varies
  depending on the reactants)
• Erlenmeyer flask (conical flask)
• Standard Solution (a solution of known
  concentration, a common one is aqueous Na2CO3)
• Solution of unknown concentration
• It is also recommended that a control is used in
  order to see the difference in colour between the
  initial and final colour

30
Procedure

• Rinse all glass ware ,the Burette, pipette and
  flask with distilled water.
• Fill the burette with the standard solution of
  HCl. Open tap and note start reading (0.0 cm3)
• Using the pippette measure 25 cm3 of the unknown
  NaOH into the conical flask.
• Place 2-3 drops of the indicator into the flask.
• Place flask below burette and add acid dropwise
  untill the colour of the indicator changes.

31
Procedure...

• Note final reading on the burette.
• Difference between final reading and first
  reading will give amount of HCl used.
• Wash and rinse flask and repeat titration 4-5
  times till your readings are very close, not more
  than 0.1 cm3.
• Calculate the average amount of HCl used.

32
Calculation
33
Calculation...

• The equation of the reaction is
• HCl NaOH --? NaOH H2O so 1mole of HCl
  reacts with 1 mole of NaOH.
• Volume of acid (Va)x concentration of acid (Ca)
  Volume of base (Vb) x conc of base (Cb)
• Ca 0.1M, Va average reading from
  titration.
• Vb 25 cm3 , Cb unknown

34
Calculation.....

• Cb Va x Ca / Vb
• So Cb is the concentration of NaOH.