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Chemistry
Acids and Bases
Year 10
Study of Chemicals and how they
react
Everything is made of chemicals
They are made of elements.
There are over 100 elements
What are Acids?
Acids are
common
Some are
dangerous and
can burn your
skin
Some are safe to
eat and drink
Stomach acid
helps digest food
Acids
•
•
•
•
A group of compounds which behave similarly
All have low pH
Turn Litmus paper RED
All donate H+ ions in aqueous solution
Examples
•
•
•
•
Hydrochloric HCl
Sulfuric H2SO4
Nitric HNO3
Ethanoic CH3COOH
explosion
Acids
Definition
A dilute acid has lots of water and a
small amount of acid
A concentrated acid has lots of acid
and not much water so must be
handled carefully
A strong acid releases lots of H+
A weak acid releases fewer H+
What are Bases (Alkalis)?
In our home we
often use bases
to clean things.
Eg Bleach and
toothpaste
Some things are
not acids or
bases, we say
that they are
neutral. Eg
Water
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Bases
Definition
• A family of compounds that behave
similarly
• Have a high pH
• Turn litmus BLUE
• All donate OH-
What does pH measure?
pH Measures the concentration of H+
ions in a substance.
H+ = Hydrogen with a positive
charge
Examples
• Ammonia NH3
• Sodium Hydroxide NaOH
PH SCALE (COPY IN NOTES)
Measuring acid strength?
Working with Indicators
Red litmus turns BLUE in the
presence of Bases
Blue litmus turns RED in the
presence of acid
Acids and bases react together in
a NEUTRALISATION reaction
The more H+ the lower the pH
To decide if something is an acid or a
base we can use an indicator.
Litmus and Universal Indicator are
examples of indicators.
They change colour depending on if
they are in an acid or a base.
Acid Reactions
Acid + Base Salt + Water
Acid + Metal Salt + Hydrogen
Acid + Carbonate Salt + Water + Carbon Dioxide
• Hydrochloric acids (HCl) form CHLORIDE salts
• Nitric acid (HNO3) forms NITRATE salts
• Sulfuric acid (H2SO4) forms SULFATE salts
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Dissociation in Water
Dissociation means completely
breaking down into ions in water
Strong Acids Completely Dissociate
in water to form ions.
Amphoteric Substances
Substances that can act as an acid or
a base
Many metals fit in this category
• Zinc, Tin, Lead, Aluminum, Beryllium
Bases and Weak Acids do not
dissociate completely
Acid Rain
Consider
Antacid Investigation
• Causes
• 70% population get
natural
human
heartburn /GERD
• $9m on 1 brand!
• Effects
buildings
flora
fauna
health
• Prevention/Solution
NZ facts 2007
• 3rd most widely
prescribed medicine
Which brand is the
best?
Identify Unknown Solutions
Review
Click Here For Review
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Rates of Reaction
Factors increasing the rate of
reaction
Metals/periodic table
, Element, compound, exo/endo
• Surface area
• Concentration
• Temperature
• Catalyst/Enzyme
• Pressure
Method
1.
2.
3.
4.
5.
Collect the 4 substances to be
tested
Place a drop of the first substance
in the spotting tile
Test the substance with a drop of
universal indicator
Record the result
Repeat steps 11-4 with the
remaining 3 substances
Results
Substance
Hydrochloric acid
Ammonia
Water
Sodium Hydroxide
Experiment write up
Title Working with Indicators
Aim To find out what happens when….
Method As previous slide, short bullet point
Diagram Half page, labels, straight lines
Results Draw your table
Conclusion Write about what you learnt from the
experiment. “Universal indicator turns blue in
bases, red in acids and green when solutions are
neutral. …was a base because it turned blue
when we added indicator. …. Was an acid as it
turned red when we added indicator. …. Was
neutral as it turned green when we added
indicator”
Universal indicator
colour
Investigate an Acid
Vinegar is an acid
Add some powders to vinegar and
OBSERVE what happens
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Dissolve – powder is soluble
Doesn’t dissolve – powder is insoluble
Fizzing – reaction is occurring gas given off
Heat – does it get hot or not
Smell – gas given off
Colour change
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Experiment time!
Method
1.
2.
3.
4.
5.
6.
Results
Substance
Experiment write up
Observations
(Dissolves, fizzes, smells etc.)
Sugar
Salt
Etc.
Acid Extension
Test series of fruit juices with
indicator
Which has most acid
Rot teeth
Write up
Collect 5 test tubes in a test tube rack
Put 1 spatula of either sugar, salt,
baking soda, flour, washing powder into
each test tube
Collect vinegar in a 50ml beaker
Add 5ml vinegar to a test tube and
observe what happens
Record results in a table
Repeat step 4 and 5 until all test tubes
are tested
Title Reactions with Acid
Aim To find out what happens when….
Method As previous slide, short bullet
point
Diagram Half page, labels, straight lines
Results Draw your table
Conclusion Write about what you learnt
from the experiment. “Some substances
are able to dissolve completely and form a
solution.. Others will not dissolve and are
solution
insoluble.”
insoluble
.”
Investigating Evaporation
When water is heated
it turns from a liquid
into a gas (steam)
This is called
evaporation
Some things dissolved
in the water will be
left behind when the
water is heated
Evaporation can be
used to separate some
solutions
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Method
1.
2.
3.
4.
5.
6.
Place 2g of salt and 10ml of warm water
into a test tube
Place thumb over the top and shake to
dissolve.
Pour 5ml of the salt solution into an
evaporating dish
Light the Bunsen and turn to a blue
flame
Heat the mixture until almost all the
water has disappeared.
Observe and record what happens
Experiment write up
Title Investigating Evaporation
Aim To find out what happens
when….
Method Short bullet points
Diagram Half page, labels, straight
lines
Results Describe what happend
Conclusion Write about what you
learnt from the experiment.
Testing for Glucose
Glucose is a sugar
Benedict’s solution is used to test for
glucose
Add Benedict’s to the sample and
heat, it turns ORANGE if glucose is
present
Forensic Scientists
Police often need
scientists to help
determine the cause
of death
This person died
holding 4 bags of
white powder (salt,
glucose, starch,
baking soda)
You must investigate
the substances and
identify what they are
Design your Experiment
You have:
• Vinegar
• Water
• Benedict’s solution
Unknown Solutions
You have been given four solutions
(glucose, salt, baking soda and vinegar)
The labels have fallen off!
Design an experiment which will allow you
to identify the solutions
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•
•
•
Evaporation
Benedict’s
Universal indicator
Water
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