2010 BT Examiner's report
H2 Chemistry 9647 Term 3 Block Test 2010 – Examiner’s report
H2 CHEMISTRY 9647
Paper 2 (Section A)
Structured Questions
Question 1 – Atomic Structure and Redox Titration
Most elements exist in nature as mixture of isotopes. At present, there are about 1600 known isotopes, of which only one-sixth are stable. The unstable isotopes lose energy by emitting ionising particles or radiation through the process of radioactive decay.
Ernest Rutherford and later Paul Villard discovered the three types of radiation:
-radiation (nucleus of helium atom); -radiation (electron); and -radiation.
(a) (i) Define the term isotope.
Answer:
Isotopes are atoms having the same number of protons / proton number / atomic number / of the same element but have different number of neutrons / different mass numbers / different number of nucleons
Comments:
Although this is a simple recall question, less than half of the students gave the correct definition. This is unacceptable, and students must make a more serious attempt to memorise
(with understanding) all the definitions for each topic.
Many students left out the word “atoms” which was crucial to the definition, and resulted in the loss of the mark.
(ii) A stream of -particles, -particles and -rays is subjected to an electric field as shown below. The path taken by the -rays has already been drawn. Sketch on the diagram, how the -particles and -particles are affected by the electric field, given that they are travelling at the same speed. Label your answers clearly.
+
-particles
source
-rays
−
-particles
Comments:
This question is only slightly modified from the tutorial question, and it required students to realise that -particles (helium nucleus) are heavier and positively charged, while -particles
(electrons) are lighter and negatively charged. Therefore, it is a pity that many students did not manage to score the fully two marks for the question.
Page 1 of 14
H2
H2 CHEMISTRY 9647
Paper 2 (Section A)
Structured Questions
Question 1 – Atomic Structure and Redox Titration
Most elements exist in nature as mixture of isotopes. At present, there are about 1600 known isotopes, of which only one-sixth are stable. The unstable isotopes lose energy by emitting ionising particles or radiation through the process of radioactive decay.
Ernest Rutherford and later Paul Villard discovered the three types of radiation:
-radiation (nucleus of helium atom); -radiation (electron); and -radiation.
(a) (i) Define the term isotope.
Answer:
Isotopes are atoms having the same number of protons / proton number / atomic number / of the same element but have different number of neutrons / different mass numbers / different number of nucleons
Comments:
Although this is a simple recall question, less than half of the students gave the correct definition. This is unacceptable, and students must make a more serious attempt to memorise
(with understanding) all the definitions for each topic.
Many students left out the word “atoms” which was crucial to the definition, and resulted in the loss of the mark.
(ii) A stream of -particles, -particles and -rays is subjected to an electric field as shown below. The path taken by the -rays has already been drawn. Sketch on the diagram, how the -particles and -particles are affected by the electric field, given that they are travelling at the same speed. Label your answers clearly.
+
-particles
source
-rays
−
-particles
Comments:
This question is only slightly modified from the tutorial question, and it required students to realise that -particles (helium nucleus) are heavier and positively charged, while -particles
(electrons) are lighter and negatively charged. Therefore, it is a pity that many students did not manage to score the fully two marks for the question.
Page 1 of 14
H2