P1249003581hdxiy - PowerPoint PPT Presentation

Title: P1249003581hdxiy


1

Demo water to milk to wine
Types of chemical reactions
How can you tell that a Reaction has occurred ?
Ruth Ng
2
Evidence of a chemical reaction

• With respect to our demo,
• Colour change. Why ?
• Phenopthalein turns pink in the presence of a
  base
• Phenopthalein turns colorless when we added an
  acid
• Production of a gas. Why ?
• Reaction of the acid with baking soda produced CO
  2
• Formation of a precipitate. Why ?
• Reaction with Ba created BaSO 4

3
Evidences (continued..)

• Any other ways to tell that a reaction occurred ?
• Odour formation
• Labs you can try
• Making esters
• ( ex Acetic acid ethanol ? nail polish
  smell)
• ( ex acetic acid pentanol ? pear smell )
• Rotten egg lab ( ZnS 2 HCl ? H 2 S ZnCl 2 )
• Heat produced
• Baking soda citric acid ( endo ? - 3 0C)
• Mg HCl ( exothermic ? 78 0C )

Safety concerns with Zn S toxic, restricted
by TDSB
H 2 S ? noxious smell, headache
Temperature Probe-ware
Egg smell
4

In groups, let s jot down some chemical
reactions we see everyday
Heres a few examples that you may have come up
with
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Chemical reactions you see around you

• Statue of Liberty appears green
• due to the oxidation of Copper.
• Cu ( blue) O 2 ? CuO ( green )
• Rusting of a nail
• Tarnishing of silver-ware
• Burning of gasoline in our car engine
• Frying an egg

6
More Chemical reactions

• Digestion of food
• Photosynthesis

7
What have we learned ?

Check the box whether or not you agree with
these Statements.
Knowing this, Lets review what we Know about
reactions
And now, on with the lesson
Chemical reactions play a big role in our lives
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Types of chemical reactions

• The 4 different types of chemical reactions we
  shall be looking at today are

• Synthesis
• Decomposition
• Single displacement
• Double displacement

Focusing on how these 4 reaction types affect our
lives
Via Lab work
Fulfils expectation MC 1.03
MC 3.03, 3.04
MCV.02
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Synthesis Reactions

• Synthesis reactions involve 2 or more substances
  combining together to make a more complex
  substance.

A cartoon example would be
H 2
O 2
In chemistry, this is analogous to

?
H 2 O
worm
small bird
Larger bird
For a neat animation
http//www.dlt.ncssm.edu/core/Chapter5-Moles-Molar
ity-Reaction_Types/Chapter5-Animations/Synthesis.h
tml
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Decomposition Reactions

• Decomposition reactions involve the breaking down
  of a more complex substance into simpler, smaller
  parts.

For example
H 2
O 2
H 2 O
?
This is analogous to

Since water can be made from and broken back into
its elements
shell
Egg hatching
turtle
This implies

• that some chemical reactions are reversible !

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What have we learned ?

decomposition and synthesis are opposite sides of
the same coin
Therefore, Chemical reactions can be reversible
12
Misconception 1

• Only physical changes are reversible.
• FALSE !
• Any ideas why this is false ?
• The ability to synthesize and decompose certain
  compounds like water prove that some chemical
  reactions are reversible !
• Why do I need to know this ?
• Reversibility of reactions lead to the concept of
  equilibrium ( which is covered in Gr. 12)

• Any physical reactions that are hard to reverse ?
• crushing of a rock or Rolaids ( STOMP )
• Breaking of an egg ( Humpty-Dumpty )

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Misconception 2

• The original reactant will vanish FOREVER after a
  chemical reaction has occurred
• FALSE
• Why is this false ?
• Based on Le Chateliers Principle ( that youll
  learn in Grade 12 ), conditions can be made such
  that H 2 can be produced from H 2 O

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Are all reactions reversible ?

This leads into the Gr.12 Concept of K and Gibbs
Free energy
Theoretically, Yes ! However, in reality, only a
few are.
Is there a possible enrichment exercise I can do ?
But, under the RIGHT conditions of temperature
Pressure, unfavorable reactions can be made to
work
15
Extension Statue of Liberty

• Statue of Liberty looks green because
• Cu (s) O 2 (g) ? CuO (s) occurs under STP
• But CuO (s) ? Cu (s) O 2 (g) requires T
  increase
• Ask students ( inquiry )
• Why does the decomposition require T increase to
  occur
• Research the specific conditions whereby CuO will
  decompose
• What is STP ? ( leads into Gas unit )

16
Extension 2 Rust ?

• Rust looks orange because
• Fe (s) O 2 (g) ? Fe 3 O 4 (s) (Rust)
• Ask students ( inquiry )
• Research the oxidation state of Fe in rust
• Why is rusting a favorable reaction ? (Link it
  with corrosion in 12C program, rates of
  reactions)
• Under what conditions can rust be made to
  decompose back into Fe ? Why? Why not ?

17
Back to more reaction types

The 2 reaction types well be looking at are
Single displacement And Double
displacement reactions
In terms of LOVE
You can think of the next 2 reaction types
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Single displacement Reactions

• Single Displacement reactions occurs when a
  single UNCOMBINED element

reacts with a compound.
to form a new element
and a new compound
For example
New couple
couple
Sad man
Single man
This is analogous to a very tragic love triangle,
where ultimately 1 person gets left out.
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SD in terms of chemistry
New couple
Sad man
To balance the following equation
couple
Single man

Ag (s)
2
( NO 3 ) 2
Cu (s)
AgNO 3 (aq)
?
2

Cu
From this reaction, we can see that
Silver metal can be extracted from a silver
nitrate solution in the presence of Copper.
http//www.dlt.ncssm.edu/core/Chapter5-Moles-Molar
ity-Reaction_Types/Chapter5-Animations/SingleDisp_
Reaction-MetalToMetal.html
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Will the reaction work if the metals are switched
?

• We know that
• Cu (s) AgNO 3 ? Ag (s) Cu(NO 3) 2 works
• But does
• Ag (s) Cu(NO 3) 2 ? AgNO 3 Cu (s) work ?
• NO !
• Since Ag is lower on the activity series than Cu,
  Ag is less reactive than Cu and cannot displace
  Cu from the Cu(NO 3) 2 solution.

Not all reactions are reversible !
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What does an activity series do ?
Metals Metal Ion Reactivity
K K reacts with water
Ca Ca2 reacts with water
Na Na reacts with water
Mg Mg2 reacts with acids
Al Al3 reacts with acids
Zn Zn2 reacts with acids
Fe Fe2 reacts with acids
Ni Ni2 reacts with acids
Sn Sn2 reacts with acids
Pb Pb2 reacts with acids
H2 H
Cu highly unreactive
Hg Hg2 highly unreactive
Ag highly unreactive
Pt Pt highly unreactive
Au Au3 highly unreactive

• ranks elements by how well they can displace
  other elements from a solution.
• Cu (s) AgNO 3 works
• But
• Ag (s) Cu(NO 3) 2 does NOT work

C u
A g
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What did we learn ?

How about applying those same metals we use to
generate our activity series to find out which
best removes Ag tarnish
Because, in order to Extract Metal B, Metal A
must be more Reactive.
How does SD reactions apply to real-life ?
Most Single displacement Reactions
are uni-directional.
In metallurgy, where metals are extracted from
its ores
Also, in the cleaning of tarnished silver-ware
Why ?
23
STSE cleaning silver-ware

• Before the lab activity, tell students what
  tarnish is.
• 4 Ag (s) 2 H 2 S (g) O 2 (g) ? 2 Ag 2 S (s)
  2 H 2 O (L)
• How do we get rid of the tarnish ?

From air
tarnish
spoon
Get yourself some Magic plates !
Cleans silver Without use of any chemicals
Magic plates. Environmentally Friendly.
24
Pre-lab what is assessed

• Given Zn, Cu, Al, Fe, Mg (strips/foil) and 5
  tarnished spoons, hot plate, water.
• To do Design a process by which they can
  determine which metal best cleans out the Ag 2
  S
• Students define criteria of best cleans
• In terms of speed of reaction
• Shininess of the surface of the spoon after the
  reaction
• Does proximity of the metals matter ?
• Any methods/ substance they can use to catalyse
  the reaction

25
Lab take-up

• The magic of the plates stems from the reactivity
  of Al
• Since Al is higher on the activity series than
  Ag, Al displaces Ag from Ag 2 S.
• 2 Al (s) 3 Ag 2 S (s) 6 H 2 O ?
• 6 Ag (s) 2 Al(OH) 3 (aq) 3 H 2 S (g)

So, save your , Clean your tarnished
silver-ware simply by using Al pie plates.
And dont forget to add a dash of your very own
Baking soda for that perfect shine !
6 e -
Clean spoon
26
Misconceptions debunked by this lab

• Chemical reactions occur when you mix chemicals
  together.
• Heat is required to kick-start this reaction.
• Chemical experiments that relate to real-life are
  expensive and difficult to perform.
• This is quite easily done.

27
Finally, the last reaction type

Double displacement reactions
Rolaids HC l demo
28
Double displacement reactions

• Occurs when 2 compounds react to form 2 new
  compounds.
• How does Rolaids add Ca to your body

CO 3
Ca
?
H
Cl

Ca
Cl 2

H 2
CO 3
2
Stomach acid
Rolaids
Source of Ca
Where does the bubbling come from ?
H 2
CO 3
?
H 2 O

CO 2
(g)
fizz
29
STSE/ case study activities for DD

• DD reactions used to extract soluble toxic heavy
  metals like Pb 2 (electronics) and
• Cr 3 (leather) eluted into the water by these
  industries
• How do we deal with illegal dumping ?
• Hair removal from animal hides ? Ca(OH) 2
• Tanning leather ? H 2 SO 4
• Ca(OH) 2 (aq) H 2 SO 4 (aq) ? CaSO 4 (s) 2 H
  2 O (L)

CaSO 4 is Gypsum (which has fire-protecting
properties) ? 12 C
Salt
Acid
Base
neutralization
30
Wrapping up

Resources
31
Thank you

The end