# Form 4 Chemistry: Radioactivity Questions and Answers

Form 4 Chemistry Radioactivity Questions and Answers.

We are going to answer questions on radioactivity. Students preparing for KCSE exams will find these questions very useful.

Lessons (**26**) * SHARE*

- 1.
(a) 100g of radioactive #overset(233)(91)# Pa was reduced to 12.5g after 81 days. Determine the half-life of Pa. (b)#overset (233)(91)# Pa decays by beta emission. What is the mass number and atomic number of the element formed?

9m 3s - 2.
Complete the diagram below to show how #alpha# and #beta# particles from a radioactive source can be distinguished from each other. Label your diagram clearly.

2m 28s - 3.
M grammes of a radioactive isotope decayed to 5 grammes in 100 days. The half-life of the isotope is 25 days. (a) What is meant by halflife? (b) Calculate the initial mass M of the radioactive isotope.

5m 57s - 4.
An isotope of Uranium #overset 234 92# U decays by emission of an alpha particle to thorium (Th) (a) Write the equation for the nuclear reaction undergone by the isotope. (b) Explain why it is not safe to store radioactive substances in containers made from aluminium sheets

3m 48s - 5.
The graph below shows the mass of a radioactive isotope plotted against time. (a) Using the graph, determine the half-life of the isotope. (b) Calculate the mass of the isotope present after 32 days.

6m 13s - 6.
A radioactive isotope #X_2# decays by emitting two alpha (#alpha#) particles and one beta (#beta#) to form #overset 214 83#Bi (a) What is the atomic number of #X_2#? (b) After 112 days, #1/16# of the mass of #X_2# remained. Determine the half-life of #X_2#.

8m 29s - 7.
Study the nuclear reactions given in the scheme below and answer the questions that follow. #overset 12 6 C overset (step I) vec# # overset 14 6 C overset (step II) vec# # overset 14 7#N (a) #overset 12 6# C and #overset 14 6 C# are isotopes. What is meant by the term isotope? (b) Write an equation for the nuclear reaction in step II
(c) Give one use of #overset 14 6#C .

2m 47s - 8.
The graph below represents a radioactive decay series for isotope H. Study it and answer the questions that follow. (a) Name the type of radiation emitted when isotope H changes to isotope J. (b) Write an equation for the nuclear reaction that occurs when isotope J changes to isotope K. (c) Identify a pair of isotope of an element in the decay series.

5m 40s - 9.
(a) State two differences between chemical and nuclear reactions. (b) Below is a radioactive decay series starting from #overset 214 83# Bi and ending at #overset 206 82# Pb . Study it and answer the question that follows. (i) Identify the particles emitted in steps I and III (ii) Write the nuclear equation for the reaction which takes place in step V

7m 44s - 10.
State two factors which determine the stability of an isotope.

1m 11s - 11.
100 g of a radioactive substance was reduced to 12.5g in 16.6 years. Calculate the half-life of the substance.

4m 46s - 12.
(a) Complete the nuclear equation below. (b) State one: (i) use of radioisotopes in agriculture (ii) danger associated with exposure of human beings to radioisotopes.

2m 2s - 13.
(a) Distinguish between nuclear fission and nuclear fusion. (b) Describe how solid wastes containing radioactive substances should be disposed off.

1m 44s - 14.
(a) A radioactive substance emits three different particles. Give the symbol of the particle with the highest mass.
(b) (i)Find the values of #Z_1# and #Z_2# in the nuclear equation below. (ii) What type of nuclear reaction is represented in b (i) above?

3m 50s - 15.
(a) Study the table below and complete it. (#W^-1# and #X^(4+)# are not actual symbols of the ions). (b) State the observation that would be made in the following tests to distinguish between: (i)Sodium and copper by burning pieces of each in air. (ii) Sodium and Magnesium by placing small pieces of each in cold water which contains two drops of phenolphthalein.

11m 35s - 16.
Carbon-14, #overset 14 6# C, is used in carbon dating. It decays to form nitrogen, #overset 14 7# N . The graph below shows the amount of carbon-14 left in a sample against its age in years.(a ) Write a nuclear equation for the decay process of carbon -14. (b)From the graph, determine the: (i) half-life of carbon-14; (ii) percentage of carbon -14 in a sample whose age is 1950 years.

4m 47s - 17.
Complete the nuclear equation below: (a)#overset 131 53l rightarrow overset 131 54X_e + #-----
(b) The half-life of #overset 131 53l# is 8 days. Determine the mass of #overset 131 53l# remaining if 50 grammes decayed for 40 days.
(c ) Give one harmful effect of radioisotopes.

3m 34s - 18.
Draw a labelled diagram to illustrate how alpha, beta and gamma radiations can be distinguished from each other.

5m 30s - 19.
(a)Distinguish between a neutron and a proton. (b) What is meant by a radioactive substance? (c) State two dangers associated with radioactive
substances in the environment. (d) The two isotopes of hydrogen, deuterium #overset 2 1 D# and tritium #overset 3 1 T# react to form element Y and neutron particles, according to the equation below:

7m 14s - 20.
Complete the nuclear reaction below: (b) State two uses of radioisotopes in health.

1m 58s - 21.
A radioactive substance weighing M kg took 1900 years for the original mass to reduce to 15 kg. Given that the half life of the radioactive substance is 380 years; (a) Determine the original mass of the radioactive substance.
(b) State two uses of radioactivity in medicine.

3m 3s - 22.
Complete the nuclear equation below (a) (b) The half-life of #overset 131 53 I# is 8 days. Determine the mass of #overset 131 53 I# remaining if 50 grammes decayed for 40 days. (c) Give one harmful effect of radioisotopes.

2m 41s - 23.
Calculate the values of X and Y in the following nuclear equation.

2m 30s - 24.
(a) Give the symbols of the two charged particles emitted by a radioactive isotope. (b) An isotope #overset 210 82 Pb# disintegrates by emitting two beta particles. Determine the mass number and atomic number of the resulting nuclide. -mass number: -atomic number:

2m 53s - 25.
The diagram below shows radiations emitted by a radioactive sample.
(a) Identify radiations: (i) M
(ii) N
(b) Explain what would happen when a sheet of paper is placed in the path of the two radiations.

2m 43s - 26.
(a) Radioactivity has several applications. State one application of radioactivity in:
(i)Medicine
(ii) Agriculture
(iii) Tracers
(iv) Nuclear power station
(b) State two dangers associated with radioactivity.

2m 9s

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