IGCSE Chemistry Paper-1: Specimen Questions with Answers 15 - 17 of 99

What is the relative molecular mass, Mr, of HNO₃?

Answer

Explanation

Relative molecular mass is the sum of all the relative atomic masses of the atoms in a molecule.

H = 1, N = 14, O = 16

Therefore

The diagram shows how to obtain pure water from seawater. Where do water molecules lose energy?

Explanation

Here, Sea water contains .

• So, to obtain pure water () , there is a process called desalination is used to convert salt water into pure water.

Desalination Process:

• In this process, sea water is heated by any Bunsen flame as shown in upper figure to convert sea water into gas state.
• Then this gas is condensed to make it liquid which is called distillation process which gives pure water.

Chemical Formula:

Element X forms an acidic, covalent oxide.

Which row shows how many electrons there could be in the outer shell of an atom of X?

Answer

Explanation

They must be 4,5, 6 or 7. For example element having 7 electrons on its outer shell such as Cl forms acidic oxide Cl207. Again element with 4 electrons on is outer shell like nitrogen forms NO₂ an acidic oxide. Therefore it can have 6 or 7 electrons.