(27)育教,日五十月正年未辛豆
1991 中學會考預習專欄
明德出版社
MILL & DALE PRESS
Metals
Na
Chemistry (22).
Ca2+(aq) +,2c Cals).
Na*(aq) + e Mg2+(aq) + 2e
報日僑
五期星
Table 1: Summary of Reactions of Metals with 02, H20 and dil, acids
3. Redox Reactions and Chemical Cells
日一月三 { 一九九一)年十八國民萃中
4.4 Part of ECS is given below
日五十月1
3.1 A
Oxygen
Water
Dilute Acid (except HNO3?
redox- transfer
involves 凸
K{s}
of electrons agront.
0 oxidising.
Li
Vigorous burning to
form oxides:
Violently in cold: H2 and beat evolved.
Explosively; My evolved.
agent.
Lot of energy evolved:
e.g. 24+
2020
2K0Y+
服時 5.
務間 5
Mg(s)
黼 艏:每日上午十時至下午五時半
Jecreasing.vigour.
A
e.g. 24) 0-2Mg0
Slowly oxidized:
Moderately in cold. 2.0. Ca + 240
Ca(OH) + H2
Reaction with steam. at increasingly high. temperaturas.
12 evolved and oxide
formed.
elg. Zn + H2(g)
Moderately;
Rate decreasing:
H, evolved and a meta!
salt formed.
elg. My(s) + 2н*(aq)
+
Zu
̇(Fe reacts reversibly
with steam. 1
ویم مسلم تیم
3.2 A simple chemical cell is a device in which a redox reaction takes place but the reducing 时 oxidising agents are not in direct contact. and the electrons transferren through an external conducting wire. Such a device converts chemical energy electrical energy.
3.3 A simple chemical cell is set-un by
just connecting two metal-metal 1065 electrode systems as shown below.
Voltmeter
Electron tion
Currant()
Metal [k,
salt
+
Zn2+(aq) + 2e7
(aq) + 2e Sn2+(aq) + 2e pa2t{aq):+20-
24*(aq). + 2e
cu?+ (aq) + 2em Ag*(aq)
+
Fels)
→ Sn(s)
→ Pb(s)
Ag(s)
Ca
W. LAM
Mg
Unit 12: Revision on
Reactivities
of
Common Metals and Chemical
41
cells
A little heat
evolved.
The Reactivity. Series
20
e.g. 2P6
-2Pb0
1.1 The Reactivity Serves is a list of
metals Cannamed - in. decreasing order of the viger of tivir reactions with ichar substances.
Pe
Sn
Ph
112 This series can He
established
hasing simply aw the rate, vigour. temperature, ou the reactions with oxygen, water and dilute acids respectively.
H
Du
Hg
Little or no
reaction.
1.3 Peseriptions of the above reactions
are summarised in Table 1,
Ag
AU
No reaction
No reaction
Table 2: Action of Heat on Common Metal Compounds
Nitrates
Decomposed to nitrite and oxygen. e.g. 2KND
Decomposed to Ametal oxideng
CO.
(s).
2-2KNG> + 02
Sulphates
Decomposed toet ozide, 02 Decomposed to
tal oxide
Solution containing
ions at 14
Solution rontsinlng ions of Mi
(a) Electrical contact between the two salutions is made by means
of
{1} a salt bridge-
U-tube
solution of an electrolyte, P.g. KNO or d. filter paper soaked wito a salt solution. e.. KNL3+
force
(2) a pornus partition. (b) The electromotive.
{e.m. f.) of.
the measured using a valve (or
vacuum) voltmeter. (c). The magnitude and the sign of
the e.n.f. measured of a cell dependom the inture of he metals N and M used to set up the cell.
Some Useful Information from the Reactivity Series
( Metal
Hydroxides
Carbonates
2.1 The relative activity, of the metals decreases cn descending the Reactivity Series. !
K
No effect
No effect
Na
(a). The .hist. : reactive. metals Fiberate H2. From cold water.
e.g. 28 + 24,0 - -*2KQH + H2191
Ca
Decomposed to
metal oxide
-(b) The
jess: reactive metals Tiberate H from steam only.
(c) Metals below 5 in the series
do not Liberale
Mg
and stream.
|20H(s)
A1*
H2
Zn
Fe
e.g. Cul
Een water
· 2Pb0 +02+ 2N02
門
or steam. es. Cu.
Żnd + CO2l
4.1 Ustig
following
Cu
Hg
2.2. Metals
above hydrogen in. Lhin Reactivity
liberate Serias cán hydrogen gas from dilute acids fexrept. HNO as shown in Table 1.
Decomposed to (metal, C2 and
Ag
Decomposed to metal, Decomposed, to
2 and NO2 [e.g. Hg(NO3)2 →→→
different single obtained usage
102..
e.g. 2Ag2tg 4Ag 2002
Hg + 2NO2
→
CO(9) e.g. 2Pb(NO212 (5)
e.g. 2Ee!
ferrochemical Series (ECS)
The
"set-up, cells are different. spective
by the
5. Using the E.G.S.
The position of a metal in the ECS gives much information about its properties,
15.1 Reducing power of the metals
The reducing power of the metal decreases on descending the ECS.:
(a) A metal higher in ECS displaces a metal lower in. series from a solution of its salt.
e.g. Zn(s) + 24g (aq)
+2Ag(s)
(b) A metal higher in ECS reduces the oxides of a metal. lower in the series to its metal.
e.g. 2Fe(s) + 3000(s) ~~ Fe2D2 (s)
+ 30u(s):
(c) The most reactive metals reduce bold water and. dilute acids to
2.5. 2K 220 ·x+(aq) + 20H*(aq)
Less reactive metals reduce steam and dilute acids to H2.
0.9. Mg(s)+H2O(g) - Mg0{s}+{s}
*laq}{g)
Zn(s)+24(aq) → [72+
The metais below hydrogen-td ECS do not reduce water or dilute acids at all.
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metal Soy and
metals (M,
e.m.f.'s
voltanter. Each time the cell has one electrode in coro i.e. the copper electrode.
Ease- Time of
of Discovery Reduction of metal
Strip of
motal (My)
1807A.3.
| 5.2 Oxidising power of the metal ions
The oxidising power of the metal ion increases on descending the ECS.
(a) The ions below zinc in the ECS.
can be reduced using chemical
reducing agents such as Ho, Ca and CO, etc.
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2.3 A metal. Ton in aqueous solution can
be displaced by another metal which,
above it in the Reactivity Series.
15
e... Cu(S)+ 2nd (aq).
+(aq)
+ 24g(s)
But, Cu(s) + 2(aq) Sun *eaction
This is equivalent to a metal at a higher position in the Reactivity Series reduces (gives electrons to) է; 1075 of a metadat a lower position. That is, the higher in positing the metals * is. the stronger a. reduciņu agent it is.
2.4 The thermal stability of the metal
N.B. A does not ford carbonate.
Tablemon Metal Oxides and Their Reduction
HONG
| Metal loxide
Na,u
White
MOO White
Effect of
heat
Reduction to Metal
CO
ally Not reduced Not reduced Not reduced
18084.0.
KONG PUBLIC
e.g.
compounds
increases
ሆነ
ZrQ
series, as shown in Table 2. Pitse of decomposition of compounds increase down the Series.
The t.ne
[Fe203
White (White to Reduced.
yellow) le.g.
P.1.
CZ00 + Pb - 002
Zn + 2 Cu +
2.5 ho
readiness of oxidising EMA metals decreases on descending tao"
Cuc
Han
Red
agas oxidazed in metant with
air
Ag Browne..
Cu has to be beated in flame.
Au does not react with air at
Aut
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4Ag + Da
3910377
3969861
19 HIWAL : 950720
2000B.C.
Microscopic Clea
slide
sheer
IBRA
Filter paper soaked with salt solution
Let.f. is negative, then the (M,) Toses. electrons more readily than copper.
If the e.n.fi is positive, then the meta:
loses (M)
electrons less. readily than copper..
4.3 IT
the metals (M,) are listed" according to the e..f.is of the balls set-up between the metals (y) adid the copper alectroke, with the most negative ...t. coming first, 咁 series
thre electrochemical (redox) series is resulted.
CARRY ON TRAVEL
+ CO
2000 c
25e+ 360
(b) The Tons of the most reactive metals can only be reduced by electrolytic processes.
Haga Na*{i} + {
(in malten
NaCl)
Nais}
15.3 Stability in Air and Storage
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The ease of oxidising the metals decreases on descending the ECS. The most . reactive metals readily oxidized by air, so, they are usually stored out of contact of air.
e.g. K in kerosene, Na in oil, etc.
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