十七國民中
育教 日八廿月十年巳己靨夏
1.7 The mass of one male of the constituent particles of a
多次入境證
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1990 中學會考預習專欄
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Chemistry (8)
substance is often known as its molar mass (M), Its unit is g mol-1.
e.g. M(Mg) = 24 g moi
報日僑
25
0.4 x
1000
0.01 nol
1.13 A Molar solution of a substance is one that contains one mole of the substance dissolved in 1. dm3 of the solution.
MOH
(1x2+32x1+16x4)
= 99 g mol
M(MnO2 ̈)
=
(55x1+16x4) 119 g mol
2.
1.8 Thus, for a substance X,
Calculations on Chemical Formulae
2.1 The empirical (simplest formula of a compound show its constituent atoms and their simplest integral ratio.
e.g. Ethane
R. Chu
Unit 5: Revision notes on chemical
calculations
類廣告
1.
Basic concepts
Mass of X in grams
n{X} =
1.
The relative atomic mass (A) of
M(X) in g moll
小字卅四個
e.g. M(CaCl2)
= 111 g mol
2.2 The
n(CaCl) in 2.22 g of CaCl2.
2.22
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an
an element is defined as the mass .of "average" atom of the element relative to the mass of an atom of carbon-12, taken as 12. exactly.
Mass of an "average"
A of an
atom of the element
12
element
Mass of an atom of carbon-12.
It is a units.
ratio and hence has RO
The mass of an "average" atom of an element is the weighted mean of the masses of all its isotopes, i.e., taking both the isotopic masses and
proportions into account.
e.g.
chlorine
exists! as પશ 37: isotopes, 7701 and 3501, in
the ratio 3:1.
Thus, A (C1) 35x3+37x1
35.5
.3+1.
1.2 The relative molecular mass (1)
of a substance is just the sum of
the relative atomic masses of all
the- atoms contained in its molecular formula.
e.g. M(H2SO) = 1x2+32x1+16x4
98
1.3. The formula mass (F) of an Jonic
compound is just the sum of the relative atomic masses of all the
atoms contained in its empirical
(simplest) formula.
8.9. Fr (Cuso 54,0)
-63.5x1+32x1+16x4+(2x1+16x1)x5-
=249.5
F ̧{Cr2022 ̃} = 52x2+16x7
constitution
= 216
= 0.02 mo!
1.9. The molar volume of a substance is the volume occupied by one Role of its constituent particles at a particular temperature and
pressure.
Malar volume
of X
=
Malar mass of X Density of X
1.10 A11 gases have the same. molar volume at the same temperature and pressure.
The molar volume of gas is about 22.4 dm at sit.p. but 24.0 dm3 et room temperature atmospheric pressure,
and
one
has an empirical formula of CHg, indicating that it is composed of C and
atoms in the ratio 1:3.
a
of formula molecular substance shows the actual number of each kind of atoms in its molecules.
= n x Empirical Formula of x where n is an integer.
·六期日五廿月一十!九八九一年八十七國民蕞中( 26 )
mole of a gas must contain the same number. (the Avogadro number)
+
of molecules.
1 mol
Q.6 What is the volume of oxygen required to burn completely a gaseous
of mixture consisting
3
i.e.
xg
Nów 1.3 g
1.3
22400: 448
X 65
40 cm3 of methane (CH) and 45 cm3 of carbon monoxide (CO)?
0.7 50
Cm3
of a mixture of methane
1 mol 22400 cm3 at s.t.p.
448 cm
at s.t.p.
(CH) and ethane (C2ll) required. 9.6 N.B. Write a separate equation for
3
exactly 115 cm of oxyger for
complete combustion. What is the composition by volume of the original mixture?
0.8 12 cm of a gasecus hydrocarbon requires 36 cm3 of oxygen for complete combustion, giving off
3 24
of carbon dioxide. Calculate its molecular formula.
the combustion of each component.
CHq(g) + 202(g) → CO2(9) + 2H20(4)
1 mol
2 mol
i.e. 1 vol.
40 cm3
2 vols (by Avogadro's
Law) 3.
? cm*
Vol of 0 required by CH1 = 2 x 40
200(g) + O2(g)
mol.
80
2002(9)
1 vol (by Avogadro's Law)
? ca
3
X
vol. of O2 required by CO = × 45
e.g. Ethane
formula of CH
has
the
molecular
Thus,
for Substance X.
a covalent
Solutions to the Problems
Molecular Formula of X
Q.1 Formule mass of Na2CO3*1020
= 286
*.* 2 mol
i.e. 2 vols 45 ca3
.. % of Na =
% of C
23x2 286 12x1
x 100
16.1
286 x 100 = 4.2
16x3
% of 0
286
x 100 = 16.8
% of H20
18x10 286
x 100 = 62.9
0.1 Calculate the percentage composition by mass of hydrated sodium carbonate (Na2C0g 10H20).
Q.2 A hydrate has the following.
percentage composition by mass: 20.25% iron, 11.5% sulphur, 23.00% oxygen and 45.30% water. Find its empirical formula.
sulphate
0.3 Hydrated magnesíum
(MgS0xH20) consists of 48.9% by mass of the anhydrous salt, what
is the value of x?
Thus, for a gas X,
n(x) =
Volume of X at s.t.p. "Molar volume of gas at S.t.p.
3.
cm3
e.g. n(C2). in 72 cm of oxygen gas
at s.t.p.
72 cm
24000
0.0032mot
1.11 The concentratin of solution is commonly expressed in terms of the number of moles of the solute ins Oncoic decimetre of the It has the unit
Calculations on Chemical Equations
.0.4 3.425 g of lead(11, III, IV) oxide (Pb) is reduced to lead using hydrogen gas Calculate
(a) the sof lead obtained, (b) the time of H gas reactes
measured at s.t.p.
3
Q.2 Mole ratio of Fe: $:0: H2O
0.5 Metal B is in Group at the
Periodic Table. 1.5 g of its Q.3 added to some dilute hydrochloric acid, 448 cm of hydrogen gas is collected at s.t.p. and 0.2 g of the metal is left behind. What is its relative atomic mass of B.
Calculations on Volumes in Gaseous Reactions
4.
mol dm This is also known as
its polarity and denoted as M. Thus, for a solute X,
4.1
Concentration of X
Amount of solute in moles
Volume of the solution in dm3
21.2 g of anhydrous sodium rbonate is dissolved in
of water to give 400 cm wolution. What is its concentration?
Now, M(NaC
106 g moi:1
of
e.g.
n(Na2CO3)
mol
one
Gay-Lussac's Law of Combining Volumes states that "when gases react, they do so in volumes which bear a
to simple ratio another, and to the volumes of the products if gaseous, provided that all volumes are measured at, or comected to the same temperature and pressure."
÷
32
20.25 11.50 23.0 45,3
56
?
:
= 0.36 0.36 : 1.44 : 2.52.
= 1:14; 7
#22.5cm3
Hence, total volume of 02 required
80 + 22.5
= 102.5 cm
0.7 N.B. Write a separate equation of
the combustion of each gas.
Let the volume of CH, be x cin
Then, the volume of Cap is
(50 - x) cm2.
0.35 0.36 1.44 2.52
0.36 0.36 0.36 0.36
:
:
CHA
+
1 mol
... its empirical formula 15
FeSO4 7H20.
1.e. 1 yol
(N.B. In the case of hydrates, the water of crystallization 15 treated as 3 single, separate unit.)
x cm
202
2 moi
CO2
+
24,0
2 vols (By Avogadro's
Lav)
3
? cm
202H6
70%
-4002
2 mol
7 mol
1.e. 2 vols
Vol. of C2 reacted with CH4*2x cm
+ 6H 20
7 vols (By Avogadro's
Law)
.. (50-x) cm3 ? cm3
val.
of 0 reacted with £246
(50 - x) cm3
total volume of 02 reacted
- 2x + 2 (50 - x)
- 115 (given)
mol
-1
-1
MIMg50,xH.
% by mass salt
120 g hol
(120+18x) noi
the ganhydrous
=
100
-
120+18x
48.9
(given)
120 120+18x
x 100 = 48.9
(It mbad be a whole
number)
Q.4 M(P5394)
= 207
Let the assh
Pb. abtained be x 3
dm3. and the el. of He used be y
Схму
3Pb + 4H20
1 mo!
+2x+102
(x+}) mcl
x mol
of NH
NH3
4 01
3 mol (3x207) 3
i.e. 1 vol
{x+) vols
x vol (By
Avogadro's Law)
XQ
e.g. It is found that 50 cm2 of nitroger reacts with 150 cm2 of hydrogen to produce
of ammonia. 100 cm) Thus, vol. of Nivol, of lig:val.
1.e. 2x + (50 - x) = 115
x = 40
Q.8 Let its molecular formula be C..
Cyfly
+
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1.4 The mole is defined as the amount
of a substance which contains "as".
many elementary entities of the
substances as there are carbon atoms in exactly 0.012 kg (12.00 g) of carbon-12.
The elementary entities refer to
any type of particles that may represent the
chemical
of the substance
under investigation, e.g. atoms,
molecules, ions, electrons, etc.
n(X)* denotes the amount substance
X in moles.
n(H20) = 0.2 mol.
1.5 It has been found that 12.00 g of
carbon-12
contains 6.02x1012
carbon atoms.
This number,
6.02x102 is called the Avogadro. number denoted 35 L. Thus, a mole
refers often
to the Avogadro of number
of particles
any particular kind, e.g. atoms, ions, molecules, cars, etc.
1.6 One mole of a substance is just its relative atomic mass (for
atoms), relative molecular MOSS (for molecules) or formula mass tfor ionic compounds or ions),
expressed in grammes.
1990 中學會考預習專
逃出版社
MILL & DALE PR155
Computer (8)
Program Language, BASIC
Reginners
All-purpose
Symbolic
Instruction
Code
K. Choy
Different machines may use different
versions of BASIC language.
The main
pody of the language is nearly the same. except the file handling technique. However the following list of operators and reserved words would be examinated in the KKCEE:
Arithmetic Operators:
Relation perators:
Logical Op mators:
AND,.0, NOT
Arithmeti Functions:
SQR
(square root)
INT
(integral part)
RND
(random number)
ABS
(absolute value)
播放:665634
SIN (sine).
COS
(cosine)
TAN
(tangent)
665622
To do (or Molarity)
Vol of solution -
concentration = 30.28
0.5 mol dm
(or, 0.5M)
1.12 The amount of a solute contained in a known volume of its solution. with ä known concentration is readily found by using the relationship below.
Amount of solute in moles
=
Molarity x vol. of
solution in dm3
9.g. (KC) in 25 cm3 of 0.4M KCl
solution
ATN
LOG
EXP
(arc tangent) (natural logarithm) (exponential of base el
String Functions:
(string concatenation), LEX, ASC, VAL, STRS, CHRS, LEFT$, MIDS. RIGHTS, STRINGS.. Input/Output Reserved Words:
PRINT, PRINT TAB, INPUT, DATA, READ, RESTORED, PRINT USING.
Other Reserved words:
DIM. STOP, END, GOTO, GOSUB, RETURN, FOR...TO...STEP, NEXT, REM, IF...THEN, IF...THEN...
ELSE, ON...GOSUB, ON...GOTO,
ON ERROR, CLS/HOME.
File Handle. Commands:
[The format, of the syntax will be defined in the question Different machines may paper. use different sets of commands due to the use of different. Disk Operating System).
OPEN, CLOSE, INPUTA, PRINT,
EOF.
Students are recommended not to use other reserved words other than those listed above. Most BASIC versions use Eut more reserved words than above. the marker may not be familiar with the syntax. Therefore no marks will be given for those structures. BASIC is a type of computer language. People may understand your meaning even you are
But not talking accurately.
the machine. accept no little mistakes. 50 please be accurate. Although BASIC uses simple English Words, it
actually not English..
Letters are recommended.
Upper
is
Case
50:150:100
=1:3:2 (simple whalesfumber
4.2 The Avogadros" taw states that equal volumes of all gases, at the sane temperature and pressure, contain an equal number of molecules.
The reverse 15 also true, i.e. equal number of molecules will have equal volume, measured at the same temperature and pressure.
volume of gas —
4.3
Avogadro's Law number of
molecules
The Avogadro's Law also explains
mol i.e.685 g (4x22.4)
Now 3.425 g yda3
(a) x : 3.425 = (3x207): 685
12 cm3 12(x+ cm3 12x cm3
Vol. of CO2 formed - 12×
= 24 (given)
3x207 RESE
x 3.425
= 3.105
X * 2
Vol. of
reacted = 12(x+2)
= 36 (given)
(b) y : 3.525 = (4x22.4): 685
y =
4x22.4
695
x 3.425
.c. 12:2 +
= 0.448 km (er
448 cm3)
why gases have the Same molar 0.5 Let A of B be z. volume at the same temperature and pressure.
This
is because one
Numeric and String Constants:
1. Numeric Constants: The values are
always the same..
(a) Integer Constant: a whole number.
(b) Real Constant: a real number. (c) Exponential notation: E
by 6.02€23.
e.g. 6.02 × 1023 may be represented
The typical limits: 10-39
to 1938
(d) The typical limits for integer
constants:
2.
of
-32766 to 32767.
String Constants: a sequence unchanged characters enclosed in quotation marky.
(a) Any special characters may appear within a string constant except the quotation mark.
(b) is necessary to distinguish numeric constant and number in a string.
from 12. e.g. 1 is different
The former is a string while
latter is the
numeric constant of
value of twolve.
ล
the
(c) Arithmetic expression inside
Quotation marks is a scring.
"1+2" is not equal to "". Arithmetic and string variables
A variable in BASIC is a name label for a memory location that stores a number or string which can be replaced by new number or string.
(1) Different versions of BASIC accept different length of variable names.
Mass of B reacted 1.5-0.2 1.3q
But it is recommended not to use more than 6 characters. The first character MUST be a letter.
e.g. NAME
CLASS A1 89
For APPLE II Version, it accepts 6 characters but only the first two
is meaningful. That is the other character from position 3 to 6 will be neglected by the machine.)
variable names are (2) Meaningful
NAME is better than N recommended. or NA for names CLASSS is better than CS or CL$ for class names,
B
- 36 (as x 2)
Bence.
y = 4
its molecular
formula
3. "PEN"
4. "23.759"
5. 167 3-255"
6. 1.234
7. -5.97E-9
B. 147537
9. 1974875
invalid string .constant close quotation marks missing.
valid string constant.
valid string constant.
invalid numeric constant, comma is not allowed.
valid numeric constant.
invalid numeric constant.
invalid numeric
constant, the exponent is too large. valid string variable..
valid numeric variable.
(3) Space,.
punctuation. marks
and
10. AS
special characters are not allowed in variables names.
11. B6
(4) Variable names must not contain
BASIC reserved words,
12. TOTAL
(5) A % is added to the end of the variable name for integer
13. MONTH
invalio numeric'
variables.
A $ is added to the end of the variable name to denote that it is a string variable.
Examples:
The following list of BASIC numbers, strings and variable names may be valid or invalid. Say whether it is numeric or string variables and correct the variable name if it is incorrect.
List
Explanation
1. "COMPUTER" valid string constant.
valid string constant.. 2.
(null string)
14. NST
15. VAR SI
16. 37M
invalid numeric variable, TO is a
reserved word.
variable. ON is a
reserved word.
invalid, it contains a special character.
invalid numeric variable, space is included.
invalid numeric
variable, first character must NOT be.
a number.
valid. integer variable.
117. COMP%
- END