Learning Lab

Worked exercises

Example 1

Write the chemical formula for compound Vitamin C. In a molecule of the compound, \(\ce{C}\) \(-6\) atoms, \(\ce{H}\) \(-8\) atoms and \(\ce{O}\) \(-6\) atoms are present.

Answer: \(\ce{C6H8O6}\)

Example 2

A molecule of sulphuric acid is heptatomic (composed of seven atoms) and contains two atoms of hydrogen, one atom of sulphur and the element oxygen. Write the chemical formula for sulphuric acid.

Sulphuric acid is made up of three different atoms: \(\ce{H\;S\;O}\). The total number of atoms in a molecule of sulphuric acid is seven. The number of hydrogen atoms in a molecule of sulphuric acid is two and that of sulphur is 1. However, the number of oxygen atoms in a molecule of sulphuric acid is not given. To find that, subtract the sum of hydrogen and sulphur atoms from the total number of atoms.
The number of oxygen atoms in a molecule of sulphuric acid is \[\begin{align*} & =7-(2+1)\\ & =7-3\\ & =4 \end{align*}\] Therefore, the chemical formula for sulphuric acid is \(\ce{H2SO4}\)

Exercises

1. Which of the following statements about an atom is correct?

1. Elements are the building blocks of atoms.
2. Atoms are visible to the naked eye.
3. Atom is the limit for the chemical subdivision for an element.
4. Only one kind of atom is present in a compound.

2. Which of the following statements about elements is incorrect?

1. Elements are the building blocks of all matter.
2. Elements are composed of one type of atom.
3. Some of the elements exist as molecules.
4. Elements are charged species.

3. Which of the following statements about molecules is incorrect?

1. All molecules are compounds.
2. Molecules are made up of two or more atoms.
3. The gaseous elements hydrogen, oxygen and nitrogen exist as diatomic molecules in nature.
4. A molecule is the smallest unit of a compound that still exhibits the physical and chemical properties of the compound.
   

4. What is the chemical symbol of the element Aluminium?

1. \(\ce{AL}\)
2. \(\ce{al}\)
3. \(\ce{Ai}\)
4. \(\ce{Al}\)

5. What is the chemical symbol for Fluorine?

1. \(\ce{F}\)
2. \(\ce{f}\)
3. \(\ce{Fe}\)
4. \(\ce{Fl}\)

6. What is the name of the element denoted by the chemical symbol \(\ce{Hg}\)?

1. Helium
2. Mercury
3. Hydrogen
4. Halogen

7. The chemical formula for fertiliser, ammonium sulphate, is \(\ce{(NH4)2SO4}\). Determine the number of hydrogen and oxygen atoms involved in a molecule of ammonium sulphate.

1. \(\ce{H}\) \(-4\), \(\ce{O}\) \(-4\)
2. \(\ce{H}\) \(-8\), \(\ce{O}\) \(-4\)
3. \(\ce{H}\) \(-2\), \(\ce{O}\) \(-4\)
4. \(\ce{H}\) \(-1\), \(\ce{O}\) \(-1\)

8. The chemical formula for glucose is \(\ce{C6H12O6}\). Determine the number of each atom involved in a molecule of glucose.

1. \(\ce{C}\) \(-6\), \(\ce{H}\) \(-12\), \(\ce{O}\) \(-6\)
2. \(\ce{C}\) \(-2\), \(\ce{H}\) \(-4\), \(\ce{O}\) \(-2\)
3. \(\ce{C}\) \(-1\), \(\ce{H}\) \(-1\), \(\ce{O}\) \(-1\)
4. \(\ce{C}\) \(-6\), \(\ce{H}\) \(-6\), \(\ce{O}\) \(-12\)

9. The chemical formula for diethyl ether is \(\ce{(C2H5)2O}\). Determine the total number of atoms present in a molecule of diethyl ether.

1. \(3\)
2. \(8\)
3. \(10\)
4. \(15\)

10. What is the chemical formula for a molecule of nitrous oxide that contains twice as many atoms of nitrogen as of oxygen and is triatomic?

1. \(\ce{NO}\)
2. \(\ce{N2O}\)
3. \(\ce{N2O2}\)
4. \(\ce{NO2}\)

11. Determine the numerical value of the subscript \(x\) in the chemical formula, \(\ce{BaS2Ox}\). One formula unit contains six total atoms.

1. \(1\)
2. \(2\)
3. \(3\)
4. \(4\)

12. Which of the following substances is a compound?

1. \(\ce{S8}\)
2. \(\ce{F}\)
3. \(\ce{Co}\)
4. CO