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Acids and Bases (AS 90944)

NCEA Level 1 Science
by

Hamish McLellan

on 11 August 2016

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Transcript of Acids and Bases (AS 90944)

Some reactions are fast (Mg + HCl) and some are slow (Fe + O ).
2
e.g. Add 1cm Mg to 2cm HCl in a test tube
e.g. Add 2cm NaOH to 2cm CuSO in a test tube
e.g. Burn 3cm Mg ribbon by igniting with a bunsen
4
Hydrogen
Fe
12
The building blocks of all matter.
Substance
Reaction in:
Universal
Litmus
acid or base?
HCl
Hydrochloric acid
NaOH
Sodium hydroxide
CH COOH
Acetic acid
NH OH
Ammonium hydroxide
H O
Water
Ca(OH)
Calcium hydroxide
3
4
2
2
+ HCl
MgCO
3

Hydrogen carbonates = HCO e.g. Zinc hydrogen carbonate =
1
0
1
Nucleus
Outside
Nucleus
neutral
-ve
+ve
Neutrons
Electrons
Protons
26
1
Mg
H
Magnesium
Iron
Mass no.
Atomic no.
Substance made up of only 1 type of atom.
ELEMENTS
Page 11-12

Groups

(column on PT) share similar reactivity...
because they have same #
valence
(outer shell) electrons.
As you go down a group the reactivity increases.
What group are these in: Lithium, Iron, Nitrogen?
Name 3 elements in group 2.
2, 8, 2
8 e
8 e
2 e
In
shells
around the nucleus.
ELECTRON ARRANGEMENT
Superscript is used for ion charges
An atom that has
gained or lost electrons
...
IONS
Try: copper sulfide silver nitrate sodium oxide
subscript
The compound formed will be
will be attracted to
IONIC COMPOUNDS
The brackets are needed to show that we want 2 of the whole thing.
So for each Mg we will need 2 Nitrates:
Magnesium Nitrate
DIFFICULT ONES
Only required for Excellence?
Balance product and reactant so no atoms are vanishing or created.
BALANCING EQUATIONS
A reaction is
Reactants

Products
  _____ + _____ → ______ + _______ 
CHEMICAL REACTIONS
Sound
RATES OF REACTION
 
 
 
 
COLLISION THEORY
Particles inside cannot
Particles on surface can react
Pain in the stomach is often caused by excess acid and this can be relieved when magnesium hydroxide neutralises the acid. Tablets of magnesium hydroxide are sold for this purpose. How would you obtain the quickest relief from pain? Explain your answer fully. 
SURFACE AREA
If a solid is broken up, the surface area of the sample is increased (
more particles are exposed
), so
more collisions per second
the rate of reaction is increased. 
TEMPERATURE
When
temperature
is increased the particles
gain kinetic energy
. This means that...
...they move faster so have
more collisions per second
...
...they have more energy so collisions are
more effective
.
CATALYSTS
A
catalyst

lowers the energy required
to have an effective collision...
...therefore there are
more successful collisions per second
...
...catalyst is not used up in the reaction.
Beryllium
hydrogen carbonate
Be(
HCO
)
Magnesium
carbonate
Mg
CO
Nitric acid
HNO
Acids
can best be described as
H+ donators
(they dissociate to give H+).

Ammonium
hydroxide
NH
OH
Sodium
oxide
Na
O
Hydrochloric acid
HCl
Sulphuric acid
H SO
Can be identified using
indicators
.
2 common types:

ACIDS AND BASES
BASE
Purple
Blue
NEUTRAL
Green
Blue
Red
BASE
BASE
ACID
ACID
Blue
Blue
Blue
Blue
Red
Red
Orange
Red
Using small samples of the universal and litmus indicators, find out if the following are acidic, basic, or neutral.
INDICATORS
STRENGTH
Some acids and bases break up in solution easily, e.g. HCl → H + Cl
THE
pH SCALE
ALKALIS
Bases that dissolve in water are called
alkalis
.
It is difficult to test the pH of bases that do not dissolve in water.
An example:
Copper oxide reacts with sulfuric acid to produce a blue substance with a neutral pH, which crystallises when the water is evaporated.
Symbol equation:
Word equation:
General equation:
H O
+ CuSO
+ H SO
CuO
Water
+ Copper sulfate
+ Sulfuric acid
Copper oxide
Water
a.k.a: acid + base…
Acid + Base → metal salt + water
METAL
OXIDES

or

HYDROXIDES

+ ACID

+ Acid
+ Salt
Metal oxide (or hydroxide)
An example:
Magnesium carbonate fizzes with hydrochloric acid. The gas produced turns limewater milky and the remaining solution can be evaporated to leave white crystals.
2
+ CO
Carbon dioxide
+ CO
Symbol equation:
Word equation:
General equation:
H O
+ MgCl
Water +
Magnesium + chloride
Hydrochloric acid
Magnesium + carbonate
Water
+ Salt
+ Acid
Carbonates = CO e.g. Magnesium Carbonate =
METAL (HYDROGEN) CARBONATE + ACID
Metal carbonate
CHEMISTRY
ACIDS AND BASES
4 credits
External
ATOMS
An atom is made up of smaller bits called…
Periodic table:
So the electron shell for Mg would be…
Shell 3 holds
Shell 2 holds
Shell 1 holds
Be S Cl Ar C
What ions will these atoms become?:
- Now has 10 electrons, 12 protons. The ion is
Electrons 2, 8, 2
e.g. for Mg:
...and become
more stable
.
...to get a
full outer
(
valence
)
shell
...
loses outer 2
Mg
2+
Cation first, anion second
Mg
2+
Cl
-
Forms an
ionic lattice.
Balance the + and – so there is
no charge
.
e.g. Magnesium chloride
each Mg will attract 2 Cl’s
Mg
2+
Cl
-
Mg
2
Cl
NO
3
-
SO
4
2-
CO
3
2-
HCO
3
-
NO
3
-
Mg
2+
Mg
2+
NO
3
-
NO
3
-
Mg(NO )
3
2
Try: ammonium sulfide, iron(III) hydroxide, aluminium sulfate
Iron + Oxygen → Iron (III) oxide
K O + HCl → KCl + H O
Na + HCl → NaCl + H
Try:
Fix: 2H + O → 2H O
Not balanced: started with 2 O’s and ended with 1 O.
E.g. H + O → H O
NOTE: Never (ever) mess with the chemical formulae (ever) (this will affect your Merit chances).
obs: Mg disappeared, gas produced (H ), temp increases
Equation: Magnesium + Hydrochloric acid → Hydrogen gas + Magnesium chloride

obs: changes colour, solid formed
Equation: Copper sulfate + sodium hydroxide → Copper hydroxide + sodium sulfate

Equation: Magnesium + oxygen → magnesium oxide
obs: Mg disappeared, bright light, white powder formed
REACTION OBSERVATIONS
The
rate
of a chemical reaction describes how fast a reaction is.
Rate can be measured by finding out:
-
how fast a reactant is used up
, or
-
how fast a product is formed
e.g. Mg + HCl → MgCl + H (gas)
How could we measure the rate?
The faster H (bubbles) are produced, the faster the reaction.
The faster the Mg is used, the faster the reaction.
The higher the temperature?
The sound it makes?
The conductivity (= saltiness) of the solution?
The pH decrease?
 A
reaction
occurs when
particles collide

…with
enough energy
to break bonds between reactants.
...in the
correct orientation
...
The more frequently
effective collisions

occur, the faster the
rate of reaction
.
Factors affecting the
rate of reaction
:
surface area
(of solids)
concentration
(of solutions)
temperature
catalysts
Stirring to dissolve a solid in a liquid increases the surface area of contact so the rate of dissolving increases. 
CO
2
2
2
2
2
2
2
2
2
Chemical reactions are noticeable due to changes (some or all of):
Reactants disappearing
Products appearing
Flame
Smoke
Gas production
Colour change
Temperature (increase or decrease)
Page 8
Page 9-10
Page 13-14
NCEAish 15
Page 16-17
This involves
cations
(+),
anions
(-), and an
ionic

bond
between them
NAMING
Anion ends in
-ide
...
...except anions with lots of O’s (end in
–ate
), like these:
WRITING FORMULAE
Page 19-21
Page 22-23
NCEAish 24-25
Page 28-29
Page 26-27
2
Carbon Dioxide
gas (CO ) is colourless, odourless, more dense than air and basic.
How do we test for it?
It turns limewater milky
In a test tube add 2 mL (about 2cm) of HCl, and add a limestone chip (CaCO
).
Bubble into limewater using a collection tube and observe over a couple of minutes.
2
3
Bases
are
H+ acceptors
(they have
OH-
, which react with acids to make water and a salt).

2
4
3
2
4
3
3
2
Acids you must know:
Base examples:

Universal
indicator


Litmus
(paper or solution)

+
-
These are
strong
acids, as there are lots of H ions.
Weak
acids don’t break up easily, so there are few H ions.
+
+



2
4
2
4
3
2-
3
-
Metal (hydrogen) carbonate + acid → H O + metal salt + CO (all neutral)
2
2


2
2
2
2
MgCO
3
Zn(HCO )
3
2
Review questions:
Page 35-37
Expt page 44
Page 38-39
Expt page 45
Rates: 48-51
Foundation: 32-33
Page 59, 61, expt pg 62
Page 62
pH OF HOUSEHOLD SUBSTANCES
Carry out the experiment on
Page 61 (57)
with:
Vinegar
Hair remover
Deodorant
Fly spray
Baking powder
Baking soda
NEUTRALISATION
The reactions you need to know about this year are
neutralisation
reactions.
This means that they involve reacting an acid and a base to get neutral products.
Since there are only 3 acids that you will get asked about, there are only 3 sorts of salts you can produce:
Hydrochloric acid
Nitric acid
Sulfuric acid
Acid
Ion produced
Salts formed
NO
SO
Cl
3
4
-
2-
-
nitrate
sulfate
chloride
Page 68-9
Page 71-72
Acids and Bases: 78-81
Practice paper: 82-87
2
2
2
Group
Period
2
Pg 63 (1-3), expt 64
(expt page 66)
Expt pg 70
Expt (Mg + HCl)
Page 57, 58, 60, 61
AMOUNT OF PRODUCTS
Reactions at
different rates
still end up with the
same amount of product
...
...because there is the
same amount of reactants
(starting material)
CONCENTRATION
As the
concentration
increases there are
more particles per mL
...
...so
more collisions per second
between reacting particles.  
Expt page 42 - 43
Page 48-51
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