Chemical Composition

An element is a substance that cannot be broken down into two or more simpler substances by chemical processes.

What is missing in this description?

Which element is found in Group 15 and Period 3?

• astatine

• nitrogen

• phosphorous

• silicon

What is the chemical formula for carbon monoxide? (You may key in the number of atoms, if any, in the normal size, e.g. H2O for water)

What is the chemical formula for ammonia? (You may key in the number of atoms, if any, in the normal size, e.g. H2O for water)

How many atoms are there in one unit of Al₂(CO₃)₃?

Scandia (Sc₂O₃) is a compound that is made of scandium and oxygen chemically combined in a fixed ratio.

• This statement is complete.

• This statement is incomplete.

• This explanation is incorrect.

Answer explanation

You need to include the ratio.

Scandia (Sc₂O₃) is a compound that is made of scandium and oxygen chemically combined in a fixed ratio of 2 : 3.

Dinitrogen tetroxide (N₂O₄) is a compound that is made of nitrogen and oxygen chemically combined in a fixed ratio of 1 : 2.

• This statement is complete.

• This statement is incomplete.

• This explanation is incorrect.

Answer explanation

You do not simplify the ratio when describing the chemical formula. If you wrote it as 1 : 2, you would be describing nitrogen monoxide (NO₂).

Dinitrogen tetroxide (N₂O₄) is a compound that is made of nitrogen and oxygen chemically combined in a fixed ratio of 2 : 4.

What does this diagram show?

• a mixture of an element and a compound

• a mixture of two compounds

• a mixture of two elements

How can one dissolve more sugar in a fixed volume of water?

• Stir faster.

• Use larger pieces of sugar.

• Increase the temperature of the solvent.

• Increase the temperature of the solute.

Yenthol dissolves in huiline. Which is the solvent?

• yenthol

• huiline