13/04/2015
Chemistry
My family and home
13/04/2015
Acids and bases (alkalis)
Used by the body,
used in other processes: such as
food, farming and chemical
industries.
Chemistry Lesson
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Safety in chemistry
Acids and alkalis (bases)
Neutralisation
Using indicators
Practical work
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Hazard signs to learn…
flammable
Corrosive
h
i
Harmful
Irritant
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Hazard signs to learn…
Radioactive
Oxidising
Toxic
Dangerous for
environment
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Safety
• Irritant- can cause a rash or itching
• Harmful-general damage to living
organisms
• Corrosive-will burn through materials
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Safety instructions
• Wear goggles
• Follow safety instructions
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Acids and bases
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• Acid- A substance that produces hydrogen
ions (H+) when it dissolves in water.
• Bases- Compounds which react with
acids to neutralise them
• Alkali- A soluble base, forms hydroxide
OH- ions in water.
• Neutral-not an acid or base
Symbols in word equations
-states of matter
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(l) liquid
(g) gas
(s) solid
(aq) aqueous-dissolved in water
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Acids and bases (alkalis)
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Acid
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• Examples of acids include :
• Vinegar, orange or lemon juice, acid rain,
stomach acid, nitric acid, sulfuric acid,
hydrochloric acids
• Used in car batteries, food and drinks,
preserving food, in body.
Acid
• Hydrochloric acid is formed when
hydrogen chloride is gas dissolves in
water.
• HCl (g)  H+ (aq) + Cl-(aq)
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Alkali (bases)
• Examples and uses include: metal
hydroxides, metal oxides, cleaning
products, stomach antacids, baking
powder.
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Alkali
• Sodium hydroxide is formed when the
solid is dissolved in water.
• NaOH (s)  Na+ (aq) + OH- (aq)
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What is an acid?
Is an alkali (OH or H)
Give a use of an acid
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pH scale
1. An Indicator is a dye that changes colour
2. Indicators can be used to find out whether a solution
is acid, alkaline or neutral
3. Universal Indicator can be used to find the pH of a
solution
• Acid – red, pH less than 7
• Neutral – green, pH = 7
• Alkali – blue, pH greater than 7
Universal Indicator and the pH scale
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Universal Indicator is a mixture of liquids that will produce a
range of colours to show how strong the acid or alkali is: 0-14
0 1
2
3
Stomach acid
4
5
Lemon juice
6
7
8
9
10
11
12 13 14
Water Soap Baking powder Oven cleaner
Strong acid
Strong alkali
Neutral
pH scale
pH scale
pH scale
Practical 1
• Test chemicals to find pH
• Use paper and liquid
• Record results in a table
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Neutralisation
1. Acids react with alkaline solutions to form a salt
and water
• Hydrochloric acid produces chlorides
• Nitric acid produces nitrates
• Sulphuric acid produces sulphates
2. Ammonia can dissolve in water to produce an
alkaline solution. This can be neutralised with acids
to produce ammonium salts
3. Indicators can monitor neutralisation reactions
Neutralisation
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An acid and alkali will neutralise each other (if the correct
amounts are used):
Acid + alkali
Salt + water
Acid + base Salt + water
E.g. hydrochloric acid + sodium hydroxide
sodium chloride + water
Neutralisation
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Acids and bases neutralise each other.
Acids form H+ (aq) ions in water
Alkalis form OH- (aq) ions in water
Acid + alkali  salt + water
H+ + OH-  H2O
The other parts form the salt.
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Neutralisation – Hydrochloric acid
Neutralisation – Sulphuric acid
Neutralisation – Nitric acid
Questions
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• Write a word equation for adding
hydrochloric acid to magnesium hydroxide
• Extension : Write a balanced symbol
equation for this reaction (difficult)
Hint
• Mg(OH)2
• MgCl2
Answers
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• Acid + base  salt + water
• Hydrochloric acid + Magnesium hydroxide
 magnesium chloride and water
• 2HCl + Mg(OH)2MgCl2+2H2O
Neutralisation – Fertiliser
Practical 2
• Titrations and neutralisation
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Useful acid-alkali reactions
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1) Hydrochloric acid is used in the stomach
to help _______. If we eat too many “rich”
foods our stomachs create too much ____ –
this is called ______. This acid needs to be
neutralised by taking indigestion tablets.
2) Soil is naturally acidic, mainly due to acid ____. This
can have bad effects on ____ and vegetable growth, so the
excess acid may need to be neutralised with an _____ .
Words – plant, digestion, indigestion, alkali, rain, acid
Quiz on acids and alkalis
Acid, alkali or both???
1) This a pH of less than 7
2) This would turn Universal indicator green
3) This is often used in cleaners or soap
4) This would turn Universal Indicator red
5) Sodium hydroxide is a common ____________
6) This would feel soapy on your skin
7) This could be a corrosive
8) This will turn universal indicator purple
9) This would taste sour
10) Lemon juice and vinegar are examples of weak _____
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Acids and metals
• Acid + metal  Salt + hydrogen
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Metals and acids
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• The more reactive the metal, the faster the
reaction
• The speed of reaction is indicated by the
rate at which bubbles of hydrogen are
produced.
• Test for hydrogen????
• Name of salt depends on metal and acid
used
Reaction of Metals and Acid
Hydrochloric acid
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• Produces Chloride salts
• Magnesium + Hydrochloric acid
Magnesium Chloride + ________
• _______ + Aluminium +Aluminium
Chloride + __________
• ________+ ________  Zinc chloride +
_________
Hydrochloric acid
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• Produces Chloride salts
• Magnesium + Hydrochloric acid
Magnesium Chloride + hydrogen
• Hydrochloric acid + Aluminium
+Aluminium Chloride + hydrogen
• Hydrochloric acid+ zinc  Zinc chloride +
hydrogen
Symbol equations
• 2HCl + Mg  MgCl2 +H2
• ____HCl + 2Al  2AlCl3 + 3H2
• 2____ + ____ZnCl2 + H2
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Symbol equations
• 2HCl + Mg  MgCl2 +H2
• 2HCl + 2Al  2AlCl3 + 3H2
• 2HCl + ZnZnCl2 + H2
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Sulfuric acid reactions
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• H2SO4 + ______ MgSO4 + H2
• 3H2SO4 + 2Al  Al2(SO4)3 + 3H2
• H2SO4 +Zn  ZnSO4 + H2
• Copy and complete write a word equation
for each.
Sulfuric acid reactions
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• H2SO4 + Mg MgSO4 + H2
• 3H2SO4 + 2Al  Al2(SO4)3 + 3H2
• H2SO4 +Zn  ZnSO4 + H2
• Sulfuric acid + magnesium  Magnesium
sulfate + hydrogen
Nitric acid
• Nitric acid reacts with alkalis, but when
reacting with metals it can produce
nitrogen oxides.
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Metal Oxides & Hydroxides
1. Transition metal oxides and hydroxides do not
dissolve in water. They are called bases
2. They react with acids to produce salts that are
soluble
3. The excess metal oxide can be filtered off
Metal hydroxide
• Metal hydroxide + acid  salt + water
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Metal oxide
• Metal oxide + acid  salt + water
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Adding acid to carbonates
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Carbonates are compounds containing carbon and oxygen. When an acid is
added to a carbonate the carbonate starts to fizz. A gas called
_________ _______ is produced.
Calcium carbonate + hydrochloric acid
CaCO3(s)
+
2HCl(aq)
calcium chloride + carbon dioxide + water
CaCl2(aq)
+
CO2(g)
+
H2O(l)
Metal carbonate
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• Metal carbonate + acid  water + salt +
carbon dioxide
Quiz