CIE Chemistry Paper-1: Specimen Questions 17 - 18 of 99
Question number: 17
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?
1 = N 2 = N 6 = Y 7 = Y
1 = Y 2 = N 6 = Y 7 = N
1 = N 2 = Y 6 = N 7 = Y
1 = Y 2 = Y 3 = N 6 = N 7 = N
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.
Question number: 18
Compound X is heated with carbon using the apparatus shown.
A brown solid is seen in test tube and the limewater turns cloudy. What is X?
copper (II) oxide
Compound X is Copper (II) oxide.
When Copper (II) oxide is heated with carbon following reaction take place:
2CuO + C - > 2Cu + Co2
When the CO2 reaches in the beaker following reaction takes place:
CO2 + Ca (OH) 2 - > CaCO3 + H2O
When carbon di oxide comes in contact with lime water it produces calcium carbonate and causes the white precipitation in the solution.