Thursday, August 25, 2011
Tuesday, August 23, 2011
Tuesday, August 16, 2011
Form 4 Revision
Chapter 2 Structure of Atom
1 Table 1 shows the incomplete information about 3 atoms; X, Y and Z.
Atom | Proton number | Number of neutron | Number of electron |
X | 8 | 6 | |
Y | 6 | 6 | |
Z | 17 | 17 |
Table 1
(a) State the name of subatomic particles that are found in nucleus of an atom.
…………………………………………………………………………………………… [1 mark]
(b) (i) What is the term of the total number of protons and neutrons in an atom?
…………………………………………………………………………………… [1 mark]
(ii) The total number of protons and neutrons for atom Z is 35.
What is the number of neutron in atom Z?
…………………………………………………………………………………… [1 mark]
(iii) Write the symbol for atom Z in the form of A X.
Z
…………………………………………………………………………………… [1 mark]
(iv) Draw the atomic structure of atom Z.
[1 mark]
(c) Atom X and atom Y are isotopes of an element.
(i) What is the proton number of atom X?
…………………………………………………………………………………… [1 mark]
(ii) Write the electron arrangement of atom Y.
…………………………………………………………………………………… [1 mark]
(iii) What is valence electron of atom X?
…………………………………………………………………………………… [1 mark]
(iv) Why atom X and atom Y has same chemical properties?
…………………………………………………………………………………… [1 mark]
(v) State one use of the isotope X in archaeology field.
…………………………………………………………………………………… [1 mark]
2 Diagram 2 shows the chemical symbols which represent three elements X, Y and Z
The letters used are not the actual symbols of the elements.
9 X 4 | 32 Y 15 | 31 Z 15 |
Diagram 2
(a) (i) What is meant by proton number?
…………………………………………………………………………………… [1 mark]
(ii) State the proton number for atom X
……………………………………………………………………………………… [1 mark]
(b) What is represented by the number 32 for the element Y?
……….…………………………………………………………………………………… [1 mark]
(c) (i) Atom Y and Z are isotopes. State the difference between the two atoms.
..……………………………………………………………………………………… [1 mark]
(ii) State one use of isotopes in daily life.
……………….……………………………………………………………………… [1 mark]
(d) (i) Write the electron arrangement of atom Y.
……………………………………………………………………………………… [1 mark]
(ii) Determine the number of valence electron for atom Y.
……………………………………………………………………………………… [1 mark]
(ii) Draw the electron arrangement for atom Z.
[2 marks]
3 Diagram 3.1 shows the arrangement of particles of substance X at different temperatures.
 |
(a) What is the physical state of substance X at
(i) 60 oC : .........................................................................
(ii) 90 oC : ......................................................................... [2 marks]
(b) State the movement of particles of substance X at 60 oC.
....……………………………………………………………………………………… [1 mark]
(c) Graph 3.2 shows the graph of temperature against time when substance X is heated from 60 oC to 90 oC. (i) What is meant by melting point?
……………………………………………………………………………………………..
……………………………………………………………………………………[1 mark]
(ii) Based on Graph 3.2, state the melting point of substance X.
…………………………………………………………………………………… [1 mark]
(iii) Explain why the temperature remains constant from t1 to t2.
...................................................................................................................................
................................................................................................................................[2 marks]
(d) (i) Substance X cannot conduct electricity in any state.
State the type of particles of substance X.
..................................................................................................................................[1 mark]
(ii) Table 3.3 shows two substances.
Magnesium oxide | |
Carbon dioxide |
|
Which substance has the same type of particles as substance X?
Tick (√ ) the correct answer.
[1 mark]
Tuesday, June 21, 2011
Monday, June 13, 2011
Monday, May 23, 2011
Wednesday, May 18, 2011
Form 5 Chapter 4 Thermochemistry
Describe an experiment to determine the heat of precipitation of silver chloride
Diagram:
Apparatus:
Measuring cylinders, thermometer and plastic cup
Materials:
0.5 mol dm-3 silver nitrate solution, 0.5 mol dm-3 sodium chloride solution
Procedure: | ||
1. 25cm3 of 0.5 mol dm-3 sodium chloride solution is measured and poured into a clean and dry plastic cup using a measuring cylinder. 2. The initial temperature of sodium chloride solution is measured and then recorded. 3. Using another measuring cylinder, 25 cm3 of 0.5 mol dm-3 silver nitrate solution is measured. The initial temperature of the silver nitrate solution is measured after 5 minutes and recorded. 4. The silver nitrate solution is poured quickly and carefully into the sodium chloride solution. 5. The mixture is stirred with a thermometer throughout the experiment and the highest temperature obtained is recorded. | ||
Result: | ||
Mass, m | c | q |
= (25 + 25) g = 50 g | 4.2 | Initial temperature of sodium chloride solution = T1oC Initial temperature of the silver nitrate = T2 oC Highest temperature reached = T4 oC => Average initial temperature = (T1+T2)/2 = T3 oC è Increase in temperature, q = (T4 - T3) oC |
Calculation: | ||
No of moles of sodium chloride used | No of moles of silver nitrate used | |
= MV/1000 = 0.0125 mole | = MV/1000= 0.0125 mole | |
Chemical equation: AgNO3 (aq) + NaCl (aq) à AgCl (s) + NaNO3 (aq) Ionic equation: Ag + (aq) + Cl- (aq) à AgCl (s) 1 mole 1 mole 1 mole Heat released = mcq = (25 + 25 ) x 4.2 x (T4 - T3) = x J 0.0125 mole of AgCl precipitated releases x J of heat energy. Therefore, 1 mole of AgCl precipitated will released Heat of precipitation, DH = x/0.0125 J = y J Thermochemical equation: AgNO3 (aq) + NaCl (aq) à AgCl (s) + NaNO3 (aq) DH = - y/1000 kJmol-1 | ||
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