Mastering Chemical Formulas Through The Criss-Cross Method

The video tutorial explains how to form chemical formulas using the criss-cross method. It begins with an introduction to chemical formulas and the importance of understanding valencies. The tutorial provides examples, including NaCl, Sodium Sulphate, Ferrous Sulphate, Ammonium Hydroxide, Zinc Sulphate, Mercury Chloride, and Lead Nitrate, demonstrating how to apply the criss-cross method to exchange valencies and form correct chemical formulas.

What is the valency of Sodium (Na) in the compound Sodium Chloride (NaCl)?

• -2

• -1

• +2

• +1

In the criss-cross method, what happens to the valencies of elements?

• They are added together.

• They are subtracted from each other.

• They remain the same.

• They are exchanged between the elements.

What is the valency of the sulphate radical (SO4) in Sodium Sulphate (Na2SO4)?

• +2

• -1

• +1

• -2

How many sodium (Na) atoms are present in the formula of Sodium Sulphate (Na2SO4)?

• 4

• 3

• 2

• 1

What is the valency of Iron (Fe) in Ferrous Sulphate (FeSO4)?

• +1

• +2

• -2

• -1

In Ammonium Hydroxide (NH4OH), what is the valency of the hydroxide (OH) group?

• +1

• -1

• +2

• -2

What is the valency of Zinc (Zn) in Zinc Sulphate (ZnSO4)?

• +1

• +2

• -1

• -2

In Mercury Chloride (HgCl2), what is the valency of Chlorine (Cl)?

• +1

• -2

• +2

• -1

What is the valency of Lead (Pb) in Lead Nitrate (Pb(NO3)2)?

• -2

• -1

• +2

• +1

How many nitrate (NO3) groups are present in the formula of Lead Nitrate (Pb(NO3)2)?

• 3

• 2

• 1

• 4