(a) Balance the nuclear equation below and hence... | WAEC SSCE - Chemistry - 1990 (Essay)

Question 1 Report

(a) Balance the nuclear equation below and hence identify Y.

\(^{238}_{234}U \to ^{234}_{92}Th + Y\)

(b) In.a tabular form, state two of the observations in the cathode ray experiment and the corresponding deductions.

Answer

(a) Balancing the nuclear equation

\[^{238}_{92}U \to\ ^{234}_{90}Th + Y\]

Balancing the mass numbers: \(238 = 234 + A \Rightarrow A = 4\).

Balancing the atomic numbers: \(92 = 90 + Z \Rightarrow Z = 2\).

So \(Y\) has mass number 4 and atomic number 2, i.e. \(^{4}_{2}He\). Y is an alpha particle (a helium nucleus), and the process is alpha decay:

\[^{238}_{92}U \to\ ^{234}_{90}Th +\ ^{4}_{2}He\]

(b) Cathode-ray experiment: observations and deductions

Observation	Deduction
The rays travel in straight lines and cast a sharp shadow of an object placed in their path	Cathode rays are made of fast-moving material particles
The rays are deflected towards the positive plate in an electric (or magnetic) field	The particles carry a negative charge (they are electrons)

(A further acceptable pair: the rays turn a small paddle wheel placed in their path, showing the particles have mass and momentum.)

Answer Details