Transcript Collapsing Can

Hydrogen Gas from the
Reaction of Magnesium
Metal With Acid
When magnesium metal is treated with acid evolution
of hydrogen gas results
Purpose
 To observe a chemical reaction
between a metal and an acid
 To measure the amount of
hydrogen gas produced
Demonstration
 Hydrogen evolution began as soon
as the magnesium metal was
added to the water
 The hydrogen was less dense than
water so it rose through it
 The hydrogen gas was able to be
collected in the buret
Concepts
1.
Single Replacement Reactions
2.
Redox Reactions
3.
Oxidation Numbers
4.
Gases
1. Single Replacement Reactions
 A single replacement reaction is of the
general form
A +
BC
AC
+
B
In order for a single replacement reaction
to occur, A must be more reactive than B
in order to combine with C
 In this demonstration
Mg (s) + HCl (g)
MgCl2 (aq)+ H2(g)
Since the reaction occurs, we must
conclude that magnesium is more reactive
than hydrogen
2. Redox Reactions
 In a redox reaction, one substance loses
electrons while another substance gains
electrons
 “Redox” is a conventional term which is a
combination of the words “reduction” AND
“oxidation”
 The substance that loses electrons is said to
be oxidized and/or the reducing agent
 The substance that gains electrons is said to
be reduced and/or the oxidizing agent
3. Oxidation Numbers (I)
 Oxidation numbers are used to
follow electron change and
determine what is oxidized and what
is reduced during a chemical
reaction
Mg (s) + 2HCl (g)
0
MgCl2 (aq)+ H2(g)
1+
2+
oxidation
reduction
Magnesium undergoes oxidation
Hydrogen undergoes reduction
0
Oxidation Numbers (II)
 It is important to understand that
magnesium gives (loses) its two
+
electrons to the H of the acid
Mg:
Starting
Materials
Mg 2+
Products
H--H
2H+
Magnesium passes its electrons to 2H+ to form H2
4. Gases
 The approximate volume of the gas
can be calculated as follows
 g Mg/Atomic Weight Mg = mol Mg
 mol Mg/22.4 mol/L X 1000 = mL
hydrogen gas
Conclusions
 The reaction in this demonstration
was a single replacement reaction
AND a redox reaction
 The reaction was a quiet reaction
 Simple gas law theory was able to
predict the approximate volume of
gas which formed
Comments
 Many metals will react with acid as
does magnesium
 The hydrogen also contains water
vapor and is therefore too wet to
burn