# Nuclear Chemistry (Radioactivity) Exam 1 and Problem Solutions

**Nuclear Chemistry (Radioactivity) Exam 1 and Problem Solutions**

**1.** Find whether _{90}^{231}Th is stable or not.

**Solution:**

n+p=Mass Number

90+n=231

n=141

where n is number of neutrons and p is number of protons.Thus ratio between n and p is;

n^{0}/p^{+}=141/90=1,56

Since ratio is greater than 1, _{90}^{231}Th has unstable nucleus and it is radioactive element.

**2.** A, B, C and D elements form compounds AC, A_{2}D and BD. If AC and A_{2}D are radioactive and BD is not radioactive compound, find whether the following compounds are radioactive or not.

**I.** A_{2}

**II.** A_{2}C

**III.** C_{2}D

**IV.** BC

**Solution:**

If a compound is radioactive, at least one of the elements of this compound must be radioactive. Since BD is not radioactive, B and D are not radioactive elements. If AC and A_{2}D are radioactive then A must be radioactive element C can be radioactive or not we can not say anything about it.

A_{2} and A_{2}C are radioactive compounds because of radioactive element A but we can not say whether C_{2}D and BC are radioactive or not.

**3.** Find number of protons and mass number of Y in given reaction below.

_{92}^{234}X + β^{-} + α → Y + γ + 2β^{+}

**Solution:**

Number of protons in left side of reaction is;

92 +(-1) + 2 =93

Thus, number of protons in right side of reaction must be 89.

Y+1.(0) + 2.(+1) = 93

Y=91

Y=91 number of protons

Mass number of reactants must be equal to mass numbers of products.

234+4=238 mass number of reactants

Y+ 1.(0) + 2.(0) =238

Y =238

Y=238 mass number of Y

_{91}^{238}Y

**4.** Find X and Y in given reactions.

I. _{19}^{38}K → _{18}^{38}Ar + X

II. _{80}^{197}Hg + Y → _{79}^{197}Au

**Solution:**

**I.** _{19}^{38}K → _{18}^{38}Ar + _{a}^{b}X

mass number and atomic numbers must be equal;

38=38+b

b=0

19=18+a

a=1 thus, _{+1}^{0}X or _{+1}^{0}β

**II.** _{80}^{197}Hg + _{c}^{d}Y → _{79}^{197}Au

80 + c = 79

c=-1

197 + d = 197

d=0 So, Y = _{-1}^{0}β

**5.** Which ones of the following statements are true for atom having following reaction in its nucleus?

_{1}^{1}p → _{0}^{1}n + +_{1}^{0}β

**I.** Its mass number increases by 1.

**II.** Its isotope is formed.

**III.** Its netron number decreases by 1.

**IV.** Its atomic number decreases by 1.

**V.** Its number of protons increases by 1.

**Solution:**

In given reaction one proton is converted into one neutron. Thus, atomic number decreases by 1. IV is true.