Transcript Acid & Alkali Hazards

Acid & Alkali Hazards
D. Crowley, 2008
Wednesday, April 6, 2016
Acid & Alkali Hazards
To know the hazards involved when using acids and alkalis
Dangers
 There are lots of acids and alkalis in the home that are relatively safe, however in
the laboratory we sometimes use much more dangerous chemicals…
 How can you tell which chemicals are safe, and which are dangerous?
 Hazard symbols are used on bottles (and vehicles) that contain hazardous
chemicals – they can be identified by anyone, regardless of language
Dangers
Explosive – can explode
Toxic – can cause death is
swallowed/inhaled/absorbed
by skin etc…
Oxidising – release oxygen or
Moderate hazard – a
oxygen containing substance
contributing to the combustion of
other substances
substance which may cause
harm in some way
Flammable – catches fire easily
Gas under pressure – gas
is contained under high
pressure
Dangers
Corrosive – attacks and destroys
living tissue
Dangerous for the
environment – pose an
environmental hazard if disposed
of incorrectly
Health hazards – pose a risk to
health, e.g. chemical may cause
cancers
Dangers – Old Symbols
Toxic – can cause death is
Corrosive – attacks and destroys
swallowed/inhaled/absorbed
by skin etc…
living tissue
Irritant – will make skin
i
red or blister
Harmful – similar to toxic,
but not quite as dangerous
h
Highly flammable – catches
fire easily
Dangers
 Hazard symbols show us why the chemical is dangerous…
 Before we carry out any experiment, we must complete a risk assessment – we
need to think about what risks there are, and what we should do if the risk
occurs…
Risks
 Today you are going to carry out an
experiment investigating household
substances, identifying if it is an acid
or alkali, as well as the pH of the
substance (using UI)
 Complete a risk assessment for the
practical (consider the risks, how we
can minimise them, and what to do if
they occur)
Risks
 Sensible laboratory behaviour as always (no running)
 Hair tied back
 No eating, and washing hands after experiment has completed
 Depending on strength of acid/alkali this could be an irritant/harmful
(blistering of skin) or even corrosive (destroys skin) if there is contact
 Goggles to be on at all times and hands to be washed immediately if acid/alkali
touches skin
 In the event of a spillage do not
try to clear it up, instead inform
me immediatly
Experiment
 Test a variety of household substances, identifying if they are an acid or alkali,
and what their strength is (pH) - record your results in a table
Substance
Acid or Alkali
pH
Substance 1
Substance 2
Etc…
Strong acid
Weak acid
Neutral
Weak alkali
Strong alkali
Acid & Alkali Examples
Strong acid
Stomach
acid
Weak acid
Neutral
Skin
Pure
water
Vinegar
Lemon
juice
Fizzy
drinks
Milk
Weak alkali
Indigestion
tablets
Blood
Strong alkali
Washing
powder
Toothpaste
Oven cleaner
Not hazardous
 Why is it that lemonade is not considered hazardous, even though it contains
lemon juice which has a pH of ~2?
 Although lemon juice has a low pH it is not concentrated enough in lemonade
to make it dangerous – although lemon juice on its own will still sting if it gets
in a cut
 The concentration of lemon juice in lemonade is very low (water has been
added to it, which increases the overall pH closer to neutral) which is why we
can drink it!