Question

The following diagram shows a distillation process. Distillation is a technique used in chemistry to purify water from dissolved impurities, mainly salts. An example is the conversion of sea water to fresh water as is done in many countries including Oman. Temperature plays an important role in distillation process and the various steps involved are as follows. 

Step1: Heating impure water to produce steam in the distillation flask. 

Step2: Steam passes through to the Liebig condenser where it is condensed. 

Step3: Condensed water is collected in the receiving flask as pure water also called distilled water. 

a) Name the process that is taking place in step1 where water changes to steam. 

b) Name the process that is taking place in step2 where steam changes to water again. 

c) Name whether step1 is exothermic or endothermic? Justify your answer. 

d) Name whether step2 is exothermic or endothermic? Justify your answer. The end-product of distillation is an element, compound or mixture? Justify your answer.

Answer 1

a) In the first step, water changes to steam and this process is called evaporation or vaporization.

b) In the second step, hot steam is getting cooled and converting to liquid. This process is called condensation.

c) Evaporation involves change of phase from liquid to vapor. In this process water absorbs heat that is water gains energy to get excited and converted to vapor and this is an endothermic process because heat is absorbed.

d) In step 2, condensation takes place in which vapor is converted to liquid in which steam has to give out heat energy and gets cooled to form liquid. So this is called exothermic process because heat is liberated.

The end product of this distillation is water which is a compound formed by combination of two elements hydrogen and oxygen. It is called a mixture when two different compounds mix together. So it is a compound.