Chemical Compound Formulas Questions

A chemical compound is a material composed of two or more distinct components chemically linked together. Chemical compounds have meaningful chemical names and formulas. A compound’s chemical formula is a symbolic representation of its chemical makeup. Chemical formulas reveal the elements that make up a compound’s molecules, as well as the proportions in which these elements’ atoms mix to produce those molecules.

Definition:A chemical formula is a technique of expressing information on the chemical quantities of atoms that make up a chemical compound or molecule using chemical element symbols, numbers, and other symbols like dashes,parentheses, commas,brackets, and plus (+) and minus (-) signs.

Chemical Compound Formulas Chemistry Questions with Solutions

Q1: The formula of a metal chloride is MCl2. What will be the formula of its nitrate?

a) MNO3

b) M(NO3)2

c) M(NO3)3

d) M2NO3

Answer: b) M(NO3)2

Explanation: The valency of chloride ions is -1. The chemical formula MCl2 shows that the valency of the metal is +2. The valency of the nitrate ion (NO3) is -1.

The correct formula for its nitrate can be obtained by the criss-cross method. Each ion’s numerical valency value can be crossed over to form the subscript of another ion.

The metal nitrate has the formula M(NO3)2.

Q2: A divalent metal M forms a salt of its sulfate in a hydrated form. A 0.10 mol of metal sulfate requires 9 g of water to form the hydrated salt. What is the correct formula for the hydrated salt?

a) MSO4.H2O

b) M(SO4)2.3H2O

c) MSO4.5H2O

d) M2SO4.H2O

Answer: c) MSO4.5H2O

Explanation: Let the formula of the hydrated salt is MSO4.xH2O, where x is the moles of H2O.

We know that, 18g of H2O = 1 mole

So, 9g of H2O = 0.5 moles

According to the given data, a 0.10 mol of metal sulfate combines with 9g of H2O (0.5 moles).

This shows 1 mol of metal sulfate will combine with 5 moles of H2O.

The correct formula for the salt is MSO4.5H2O.

Q3. Write the general rules for writing chemical formulas.


The rules that you have to follow while writing a chemical formula are as follows:

  • The valencies or charges on the ion must balance.
  • When a compound contains a metal and a nonmetal, the metal’s name or symbol comes first. Magnesium oxide (MgO), sodium chloride (NaCl), iron sulfide (FeS), zinc oxide (ZnO), and so on, where oxygen, chlorine, and sulfur are nonmetals and are written on the right, whereas magnesium, sodium, iron, and zinc are metals and are written on the left.
  • The number of ions present in a compound created using polyatomic ions is expressed by enclosing the formula of an ion in a bracket and writing the number of ions outside the bracket. Ca(OH)2 is an example. The bracket is not required if the number of polyatomic ions is one. .For instance, KOH.

Q4. Give the compound names represented by the following formulas.

  1. NaNO3
  2. Al2O3
  3. HCl
  4. Mg(OH)2
  5. CaCO3


The positive atom or ion appears first in a formula, followed by the name of the negative ion.

  1. Sodium nitrate
  2. Aluminium oxide
  3. Hydrogen chloride
  4. Magnesium hydroxide
  5. Calcium carbonate

Q5. How many atoms are present in the following compounds or ions?

  1. NaHCO3
  2. SO32-


  1. In NaHCO3, six atoms are present in total. Amongst the six, one is sodium and one is hydrogen, one is carbon and three are oxygen atoms.
  2. In SO32-, four atoms are present in total. Amongst the four, one is sulfur and three are oxygen atoms.

Q6. A metal M forms a volatile chloride with a vapor density of 94.8. What will be the formula of the metal chloride if it contains 74.75% of chlorine?

a) MCl2

b) MCl

c) MCl4

d) M2Cl

Answer: c) MCl4

Explanation : Let the formula be MClx, where x is the number of chlorine atoms.

Molecular weight of the volatile compound = 2 Γ— Vapor density

= 2 Γ— 94.8

= 189.6 u

Mass of chlorine(in compound) = Gram weight of the compound Γ— % chlorine in the compound

= 189.6 Γ— (74.75/100)

= 141.7 g

Weight of one chlorine atom = 35.5 g

Number of Chlorine atoms,x = Mass of chlorine/ Weight of one chlorine atom

= (141.7 g) / (35.5 g)

= 4

The correct formula for the metal chloride is MCl4.

Q7: Calculate the formula unit mass of CaCO3.


Formula unit mass = Atomic mass of Ca + Atomic mass of C + (3Γ— Atomic mass of oxygen)

= 40 + 12+ (3Γ—16)

= 100 u.

Q8 : A metal M forms two chlorides of the form MCl2 and MCl4 respectively. To which group can the metal be placed?


The chemical formula MCl2 and MCl4 reveal the oxidation state of metal as +2 and +4 respectively. These oxidation states are common for Group 14 (Carbon family) of the periodic table. The general valence-shell electronic configuration of Group 14 elements is ns2np2. They can lose all the four valence electrons to give +4 or two p-electrons to give +2 oxidation states.

Thus, the metal belongs to Group 14 of the modern periodic table.

Q9: The chloride of the element X has the molecular formula XCl. Which of the following will be present in the same group as X?

a) Mg

b) Al

c) Zn

d) Na

Answer: d) Na

Explanation: The chloride ion exists as Cl showing a charge of -1. A chemical formula of a compound is overall neutral. This causes metal to exhibit +1 oxidation state. Such oxidation state(charge) is shown by Alkali metals. The only alkali metal present here is Na(Sodium).

Q10: Match the chemical names in column 1 with their respective chemical formulas in column 2.

Column 1 Column 2
a) Ammonium Hydroxide i) SiO2
b) Zinc sulfate ii) Zn(CH3COO)2
c) Silicon dioxide iii) K2Cr2O7
d) Potassium Dichromate iv) NH4OH
e) Zinc acetate v) ZnSO4

Answer: a-iv), b-v), c-i), d-iii),e-ii)

Q-11: How many grams of oxygen are present in one mole of magnesium carbonate MgCO3?

(Atomic mass of O = 16 u)


1 mole of MgCO3 contains 3 atoms of oxygen.

1 atom of oxygen has a mass = 16g.

Thus, 3 atoms will have mass = 3Γ—16

= 48 g

Q-12: What is the chemical formula of pyrosulfuric acid?

Answer: Pyrosulfuric acid is also known as disulfuric acid or oleum. Its chemical formula is H2S2O7.

Q-13: A compound with molecular formula Cr2(SO4)3 would be called:

a) Chromium sulfite

b) Chromium(II) sulfate

c) Chromium(III) sulfite

d) Chromium(III) sulfate

Answer: d) Chromium(III) sulfate

Explanation: The positive radical is chromium ion(Cr3+) and the negative radical is sulfate ion (SO42-). While writing the chemical name, the positive radical name is followed by negative radical eliminating ion in the final chemical name.

The correct name will be Chromium(III) sulfate.

Q-14: A hydrocarbon contains 75% of carbon. Then its molecular formula is

(Given: Atomic mass of C=12 u , Atomic mass of H= 1u)


Let the mass of hydrocarbon be 100g

Mass of Carbon = 75g

Mass of Hydrogen = 100-75= 25g

Calculate moles for each element:

Mole is the ratio of an element mass to its molar mass.

Moles of Carbon = 75/12= 6.25g

Moles of Hydrogen= 25/1= 25g

Divide the moles with the simplest number(6.25) to get the simple mole ratio of elements.

Simple mole ratio of C:H = 1:4

Hence the molecular formula will be CH4.

Q-15: List the three main types of chemical formulas.


The three types of chemical formulas are:

  1. Empirical Formula
  2. Structural Formula
  3. Molecular Formula

Practise Questions on Chemical Compound Formulas

Q1. What do you understand by the term chemical formula?

Q2. Write down the formulae of the following

  1. Copper nitrate
  2. Calcium chloride
  3. Sodium sulfide
  4. Magnesium hydroxide

Q3. If the formula of the metal sulphite is MSO3, give the formulae of its

  1. Hydrogen phosphate
  2. Nitrate

Q4. Give the name of the elements present in the following compounds.

  1. Baking soda
  2. Slaked lime
  3. Milk of Magnesia

Q5. Calculate the formula unit mass of sulphuric acid.

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