育敦崙華
A moderately concentrated aqueous solution of copper sulphate electrolysed The cathode is pure copper whilst the anode is copper contaminated with a small amount of zine, iron, lead and alver. With the help of ionic equations, explain what happens
at the anode,
報日僑華
三期星 日二月六年—七九一曆公年十六國民華中
買二第駭四第日十初月五年亥辛厮复
WAH KIUL
英中會考數學A(三)答案(續)
英中會考化學科試題
CHEMISTRY
SUGGESTED ANSWERS. TO MATHEMATICS PAPER II1
CONVENTIONAL QUESTIONS
SECTION. A
HONG KONG CERTIFICATE OF EDUCATION EXAMINATION : (ENGLISH) 1971
3
Fine allowed. One hour and fifteen minutes
Givens
To Calculater
Calculation
BL AB ABCD
8:30 am 9.45 am,
a aquare
Answer THREE questions only
A 90°
£2 ('' LADI. - 90°) LAB - 90°3
Give labelled diagrams, chemical equations and structural formulae where appropriate
erefore,
•MAB// DE).
(Sidea.
ZADE
ABI
25 - 12
AADE and AABL are congruent. *AE
Atomic weights: H=1. C-12; 016. Ca = 40. Cu = 63·5j
Name, and explain the bonding that usually occurs
when's metal combines with a non-metal
when two non-metals combine
When potassium chlorate decomposes to ton potassium chlonde and oxy
show by diagrams-the electrome structure of the products.
state the properties you would expect the products to have because of their particular type of bonding
student heats some dark brown lead dioxide in test tube holding a glowing splint at its mouthAfter the splint stops burning, he puts the residue aside to cool. He notices that its colour has become vellow He now takes part of this residue and adds dilute sulphuric acid to it. the residue does not dissolve. however, its colour changes to white but only on the surface
He then takes the other part of the yellow residue and dissolves it in dilute nitric acid When the reaction stops, he filters off the undissolved material (which he discards) and then adds dilute sulphuric acid to s portion of the filtrate The other portion he puts aside for a further experiment
fa) Explain all the reactions that take place
How would he obtain pure dry lead hydroxide fro the portion of the filtrate he has put aside
英中會考化學科答案
HONG KONG CERTIFICATE OF EDUCATION EXAMINATION (ENGLISH) 1971
STED ANSWERS TO CHEMISTRY (Conventional Section)
When a metal combines with a non-metal, an electrovalent bond is usually involved. An electrovalent bond is one formed by the transfer of one or more electrons from one atom or radical to auother,
at the cathode
ff in the solution.
a
on passed si jualan de
How many grams of copper will be deposited in one hour by a current of 2 amperes?
When ethanol, sodium dichromate, and sulphuric acid are used to prepare acetic acid, state the purpose of each of the three reagents, and the conditions under which the reaction will yield the maximum amount of acetic acid. (Diagrams are NOT required:)
What type of reaction occurs when chlorine-reacts with
a saturated hydrocarbon,
an unsaturated hydrocarbon 2
Illustrate your answer, with one example of each type of reaction, giving the appropriate equation and naming the product(s) formed in each case,
Two moles of ethane, on complete combustion, produce x litres of carbon dioxide at NTP and y grams of water. Determine
and V
· Using concentrated hydrochloric acid and manganese dioxide, how can pure, dry chionne be prepared and collected in the
·laboratory ? Draw a labelled diagram of the apparatus used..
State, giving equations, what products are obtained when the following nitrates decompose on healing.
sodium marzie
tead nitrate
(i) silver nitrate
12.5 grams of limestone are treated with excess dilute nydrocnion acid. The gas evolved is completely dissolved a solution o sodium hydroxide whose weight is thereby increased by grant Give equations for the reactions that take place and calculate the
us the stor percentage of ciiciuni
Since ADED is a cyc quad
ore
and
So,
Therefore
•/3 (Equal chords subtend equal angles) 12
ABDC 16 isoacles,
(b) To prove PQRS 18 ■ rectangle
Proof
Therefor
PQ, QR and ES.
12 and 13.
· /PSR = 12 + 13 •
Similarly, (PQR
[DSQ = (ROS (** AB//CD
/DSQ - LAQS
***. 23 = 25
Therefor Similarly, Therefore
QP. // RS
//PS
PQRS
PQRS La
parallelogram (Two pairs of
// sides)
/3 (Zs in the same segment)
parallelogram with right-angle)
A metallic element has one, two or three elec- trons in its outermost electron shell called the valency shell, A non-metallic element, on the other hand, has four to seven electrons, in its outermost. Electron shell. Now atoms combine so as to attain the atable outer octet (or duplet) of electrons, that is, having eight electrons in the outermost shell characteristic of the inert gases like neon and argon. It requires less energy for a metallic element to lose its few electrons in the outermost: shell, than to acquire more electrons to complete.. an octet. Similarly, it requires less energy for nonmetallic element to acquire a few more electrons than to lose all the electrons in the outermost shell in order to have a complete outermost octet. A metallic atom thus transfers from its outermost electron shell a number of electrons equal to its
valency to the outer electron shell of a non- metallic atom with which it combines. By this means, a stable electron octet is left behind in the metal and created in the non-metal. The metallic atom becomes a positively charged ion or cation whilst the non-metallic aton becomes a negatively charged ion or anion. These oppositely charged ions there- fore attract each other, and the bond between them de known as an electrovalent bond
Thus, for example, a sodium atom (2,8,1) will lose its single electron in the outermost shell to chlorine atom (2,8,7), and the ions will attract. each other by electrostatic force,
Na Na e
(11) When two non-metals combine, a covalent bond i
usually involved. A covalent bond is one formed. as a result of the sharing of two electrons, one from each aton. It requires a lot of energy to remove all the electrons in the outermost shell or to gain more electrons to acquire a complete octet By sharing electrons, each non-metallic atos will acquire a complete octet of electrons.
Thus, for example, two chlorine atoms (2,8,7) combine by sharing two electrons, one from each atom to form a molecule. The bond between them known as & covalent bond,
Potass
2 shared pa": of electrons
(5) (11) Potassium chloride is an ele trovalent tonic) compound and thus is expected to show the foll
ties:
It exists as a crystalline solida
2. It has high melting point and high boiling
point (ie, non-volatile).
It consists of charged ions.
It is an electrolyte, ie, it conduct electricity when molten or dissolved, It is insoluble in organic solvents, 8.g. alcohol, carbon tetrachloride, ether, petrol.
Oxygen exist as covalent molecules. It is expected. therefore to show the following propertiess
It exists-as-a-gas or a liquid.
2. It has low melting point and boiling point
(1. volatile).
It consists of uncharged molecules.
It is not an electrolyte, i.e. it does
conduct electricity.
It is soluble in organic solvents.- "?"
When dark-brown lead dioxide is heated, lead mono xide and oxygen are formed. The oxygen will rekindle a glowing splint, Lead, monoxide is reddish-br when hot but yellow when cold:
2Pb02Pb0 02 ↑
When dilute sulphuric acid is added to the residue which containe lead monoxide (litharge), the latter does not dissolve because it reacts slowly wit the sulphuric acid to form an insoluble white coating of lead sulphate which prevent further reaction.
Pbo + H2SO, PbSQ; * £0.
When the other part of the yellow residue con taining lead monoxide is dissolved in dilute nitric acid,
a solution of lead nitrate is formed.
PbO + 2HNO
Pb(NO)2 HO
When the reaction stops, the undisolved ma- terial, which may contain lead monoxide and lead dioxide, is filtered off, When dilute sulphuric acid is added the filtrate of lead nitrate, an insoluble whii
re pre- eipitate of lead sulphate is formed by double decomposi tions
Pb(NO) • H250, - PbSo
2HNO
The filtrate is solution of lead nitrate. From this he can prepared hydroxide by adding to it, glow ty ammonia solution solution of sodium or potassium hydroxide. A white gelatinous precipitate of lead hydro- xide is forned:
•Pb(NO3)2 + 2NaOH →→→ Pb(OH), ZNANO
With sodium or potassium hydroxide solution (but not ammonia) he should be careful not to add an excesa as lead hydroxide combines with an excess of alkali co form
a
soluble plumbites.
Pb(011) 2 + 2N2011
13 7 15 LAPES ARD
(1) and (2),
(2)
get, LAQE > ZAPU > ZARB
(288)
(288)
Oxygen molecule
The lead hydroxide can then be filtered and washed. several times with distilled water. Finally, it can be dried on a watch glass over a beaker of heated water. Heating of the hydroxide should be avoided as it would decompose the hydroxide into water and the oxide. (TO BE CONTINUED)