Acids and bases

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Acids and bases

• Teacher Claudia De Candido
• Tutor Elena Monti
• ITC O.Mattiussi 2005/06

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Menu

• What is a (n)
• acid, base
• Acid/ base indicators
• Acid/base reactions
• Acid rain
• Assessment multiple choice, true or false,
  crosswords, substitution table, interview.

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Time

• 10 class periods 50 min. each.

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Objectives

• In this unit the students will
• learn about properties and uses of acids and
  alkalis
• use indicators to classify solutions as acidic,
  alkaline or neutral
• use the pH scale to compare the acidity and
  alkalinity of different solutions
• begin to explore neutralisation and other
  reactions of acid
• learn about sources and consequences of acid
  rain
• recognise hazards linked with acids and alkalis .

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Skills

• Knowledge of the new words and the new concepts.
• Accurate explanation of the behaviour of acidic
  and basic solutions.
• Knowledge of the causes and consequences of acid
  rain.
• Prediction of behaviour through the acquainted
  knowledge.
• Grade Level second classes - secondary school.

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Evaluation

• During the lessons the students can evaluate
  their own improvements through activities single
  or in group.
• Assessment
• indicator chart, multiple choice, mistakes maze ,
  crosswords, substitution table, interview with
  acids and bases.

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Suggestions

• What the students need to do
• Ask, ask, ask if you dont understand.
• During the experiments follow instructions
  carefully.
• Take notes and take part in the lessons.
• Practice and revise even when we dont tell you.

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Safety

• Wear chemical splash goggles for the acidic and
  basic solutions.
• Normal laboratory care is needed.

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Procedure

• Show the students acids and bases used in
  everyday life. Outline basic characteristics e.g.
  acid food is sour tasting alkalis are often
  soapy, bitter and slippery.
• Show how they can be tested and determined using
  indicators (universal indicator and
  phenolphthalein ). Students will learn about pH
  numbers and colours for varying acid and alkali
  strengths and neutral, and fill in the indicator
  chart. Ask them some questions.
• Drop some acid in a base and the base in an acid
  and observe the behaviour of added
  phenolphthalein and explain it. Show the effects
  of an acid dropped on limestone and on
  magnesium.
• Collect all observations to describe the acid and
  bases and formulate a theory.
• Explain what the acid rain is like , how it
  forms, which effects it produces.

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Resources required

• Various acids and alkalis, universal indicator
  paper /phenolphthalein.
• Test tubes, hydrochloric acid, sulphuric acid,
  nitric acid, sodium hydroxide, potassium
  hydroxide, ammonia,baking soda, wine, vinegar,
  limestone, magnesium.
• Projector, computer, power point presentation.

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Where do we find acids?

• Acids are found in
• citrus fruits ( lemon juice, orange juice)
• vinegar, wine, coca cola
• car batteries ( sulphuric acid)
• our stomach (hydrochloric acid)
• acid soils
• bee stings
• acid rain

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Useful acid facts

• Ascorbic acid is another name for vitamin C.
  this chemical is found in fresh fruit and
  prevents a deadly disease, the scurvy.
• Citric acid helps make the taste of the juice.
• Salicylic acid is used to make aspirin.
• Amino acids are molecules that join to make
  proteins.

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Where do we find alkalis ?

• Alkalis are found in
• oven cleaners (sodium hydroxide)
• soap
• cleaning fluid
• milk of magnesia
• baking soda
• Alkalis are often found in substances for
  cleaning.

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What of these adjectives can be linked to an acid
or to a base?
cleaning
caustic
corrosive
sour
dangerous
soapy
fuming
harmful
irritant
slippery
edible
bitter
toxic
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Sour and bitter

• What part of the tongue can taste a lemon or
  other sour things?
• Where might you taste something bitter like
  baking soda?

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Hazard simbols

• These symbols are showing the common safety
  hazards of the acids and bases.
• Toxic can cause death, if swallowed, breathed
  in or adsorbed through the skin.
• Corrosive attacks and destroys living tissues,
  including the eyes and the skin.
• Harmful similar to toxic but less dangerous.
• Irritant not corrosive but can cause reddening
  or blistering of the skin.

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Definition of acid and base

• The definition of acid and base is based on its
  experimental behaviour.

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Universal indicator

• Indicators are chemicals that have different
  colours in acidic and alkaline solutions.
• Universal Indicator (pH paper) is a special
  indicator. It has many colours that tell us if
  the solution is acidic, neutral or alkaline and
  how strong the solution is.

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Indicators

• Indicator acid neutral
  alkali
• Universal indicator red green purple
• Litmus red blue
• Phenolphthalein colourless colourless pink

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pH

• Using the Universal Indicator and a chart you
  can read off a number - the pH number. The pH
  number usually ranges from 1-14. 1-6 means the
  solution is acidic, 7 is neutral and 8-14 is
  alkaline.

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Indicators
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pH
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pH
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Why does the indicator change colour?

• Acids release hydrogen ions in water.
• water
• HCl H(aq) Cl- (aq)
• Bases release hydroxide ions in water.
• water
• NaOH Na(aq) OH- (aq)
• These ions are responsible for the changes of
  colour.

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Strong acids and bases

• Stronger acids give up more protons (the
  positively charged parts of atoms) stronger
  bases give up more OH- (hydroxide). Neutral
  substances have an even balance of protons and
  OH-.

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Weak and strong acids

• The strong acids have the lowest pH
• (pH 0-1).
• The strong alkalis have the highest pH
• (pH 13-14)

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pH

• The pH scale is a measure of how acidic or
  alkaline a solution is. It shows the
  concentration of hydrogen ions in a solution.

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Neutralisation

• When an acid reacts with a base and they produce
  salt and water, the reaction is called
  "neutralisation."
• The acid supplies the H and the base supplies
  the OH- which combine to form water.

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Neutralisation

• The reaction is
• acid alkali neutral salt water
• The type of salt produced depends on the metal in
  the alkali used and on the acid used.
• HCl(aq) NaOH(aq) NaCl(aq) H2O(l)
• Cl- Na
• H OH-

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Reaction with limestone

• An acid (hydrochloric acid) reacts with limestone
  , producing CO2 .
• 2HCl (aq) CaCO3 (s) CO2(g)
  CaCl2(aq) H2O(l)

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Reaction with metals

• An acid (hydrochloric acid) reacts with magnesium
  producing hydrogen.
• Mg(s) 2HCl(aq) MgCl2(aq) H2(g)

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Typical properties of acids

• sour taste
• corrosive
• react with bases
• turn universal indicator into red
• generate CO2 from limestone
• generate H2 with metals
• release hydrogen ions
• have a pH less than 7.

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Typical properties of bases

• bitter taste
• soapy feeling
• turn universal indicator into blue
• react with acids
• have a pH of more than 7
• are also corrosive
• bases are also called alkalis.

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Strong acids

• The common strongest acids are
• hydrochloric acid (HCl)
• sulphuric acid (H2SO4),
• nitric acid (HNO3).

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Common bases

• Common bases are
• sodium hydroxide (NaOH)
• potassium hydroxide (KOH)
• calcium hydroxide ( Ca (OH)2 )
• ammonia
• The soluble oxides and hydroxide of metals form
  alkaline solutions.

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Solutions

• 1-a
• 2-c
• 3-d
• 4-b
• 5-a
• 6-a
• 7-b
• 8-b
• 9-b
• 10-a
• 11-b
• 12-d
• 13-d
• 14-b
• 15-c

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Ammonia
for cleaning kitchen
for popular fertilisers ammonium nitrate and
ammonium sulphate
it is irritant
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You are to be interviewed as if you are
hydrochloric acid. Read the information below to
answer.
Hydrochloric acid (HCl)

• It is corrosive for some metals (magnesium).
• It dissolves limestone.
• Part of gastric juice, it aids in the digestion
  of protein.
• Sold commercially as Muriatic acid.

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You are to be interviewed as if you are acetic
acid. Read the information below to answer.
The formula is CH3COOH
Acetic acid is
used in the manufacture of plastics used in
making pharmaceuticals the acid present in
vinegar a weak acid. It has sharp smell.
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You are to be interviewed as if you are
phosphoric acid. Read the information below to
answer.
The formula is H3PO4
Phosphoric Acid is

• a flavouring agent in sodas
• used in the manufacture of detergents
• used in the manufacture of fertilisers
• used to dissolve calcium carbonate in the taps.

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You are to be interviewed as if you are nitric
acid. Read the information below to answer.
The formula is HNO3
Nitric acid

• It is used in the production of fertilisers.
• It is used in the production of explosives.
• Nitric acid is a volatile acid its reactive
  components evaporate easily and are irritant.
• It is a strong acid.
• It stains proteins (including skin!).

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Indigestion and antacids

• The stomach produces hydrochloric acid to help
  digest food. The pH ranges from 0.9 to 1.5. When
  too much food is eaten, too much acid can be
  produced and the pH can become too low. This is
  called indigestion.
• Antacids are bases that neutralise the excess
  acid. Many contain bicarbonate or carbonate
  salts, which are basic.

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Hydrangea

• You can use flowers to detect acid and
  bases.Hydrangea plants produce pink and white
  flowers when the soil is alkaline and blue
  flowers when its acid.

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Treating stings

• Bee stings are acid. You can ease the pain with
  a weak alkali (bicarbonate of soda)
• Wasp stings are alkaline. You can neutralise them
  with vinegar (ethanoic acid)

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Making predictions

• Which substance do you think can clean this penny
  better?

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• Acids are better penny cleaners. In fact, if you
  were to leave a penny in vinegar or lemon juice
  for several days, small pieces of the penny would
  eventually start to come off. Drain cleaners, on
  the other hand, are mostly bases. Bases do not
  damage metal pipes like an acid cleaner would.

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Other experiments

• An egg in acid (acid dissolves the shell).
• A bone in acid (acid dissolves salts of calcium).
• Milk lemon juice (milk curdles, because its
  molecules are broken down by the citric acid of
  the lemon).

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Acid rain

• Most combustions give off sulphur dioxide and
  nitrogen oxides which cause acid rain.

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Consequences on vegetation

• Increased acidity in the soil leaches important
  nutrients.
• Many trees have been seriously affected by acid
  rain.

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Consequences on lakes and rivers

• Aquatic life is also highly sensitive to pH.
  Below pH 6 the number of sensitive fish declines
  and below pH 5.0 many microscopic species
  disappear. Below pH 4.0 lakes are effectively
  dead.

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Consequences on buildings

• Stone, such as marble, that contain calcium
  carbonate is eroded by acid rain.

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Consequences on human health

• The acids irritate the mucus membranes and
  increase the risk of respiratory illnesses, such
  as asthma, bronchitis, and emphisema.

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Consequences of the pH change
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Acid soil

• If the soil is too acid , most crops will not
  grow well. Farmers can spread limestone on the
  soil to neutralise it.

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Questionnaire - Write down the answers after
power point presentation.

• What gases cause acid rain?
• What pH is rain naturally?
• Where do the acid rain gases come from?
• How are the acid rain gases formed?
• What specific problems does acid rain cause in
  the environment?
• How can acid rain be reduced?
• Give 3 different ways.

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Reducing acid rain and its effects

• It is much better to reduce the sources of acid
  rain than to treat the effects
• Use less electricity at home and at work, so that
  less fossil fuel is needed to generate it.
• Generate electricity using alternative methods
  that dont release the acid rain gases e.g.
  nuclear power station, wind turbines,
  hydroelectric schemes
• Use vehicles less, walk or cycle more, especially
  for short journeys.

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