CIE iGCSE Co-Ordinated Science C12.5 Identification of ions and gases Exam Style Questions Paper 3
Question
A teacher reacts sodium with water.
Hydrogen and aqueous sodium hydroxide are the products of the reaction.
(a) Balance the symbol equation for this reaction.
2Na + ………H$_{2}$O ……..NaOH + H$_{2}$
(b) Before sodium is added to water, the water is neutral.
Aqueous sodium hydroxide is an alkali.
(i) State the pH number of pure water.
pH = …………….
(ii) Suggest the pH number of the aqueous sodium hydroxide.
pH = …………….
(c) The reaction between sodium and water is described as violent.
Describe the reaction between potassium and water.
Explain your answer.
reaction …………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
explanation ……………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
(d) Sodium reacts with chlorine to make sodium chloride.
In this reaction, sodium atoms form sodium ions and chlorine atoms form chloride ions.
• the electronic structure of a sodium atom is 2.8.1
• the electronic structure of a chlorine atom is 2.8.7
(i) Deduce the electronic structure for a sodium ion.
………………….
(ii) Deduce the electronic structure for a chloride ion.
………………….
(e) When concentrated aqueous sodium chloride is electrolysed, gases are released at each inert electrode.
State the names of the gases released at each electrode.
gas at cathode …………………………………………………………………………………..
gas at anode ………………………………………………………………………………………
▶️Answer/Explanation
Ans: 8(a) 2Na + 2H$_{2}$O→2 NaOH + H$_{2}$ ;;
8(b)(i) 7 ;
8(b)(ii) 8–14 ;
8(c) even more violent/explosive ;
reactivity increases down the group/potassium is more reactive than sodium ;
8(d)(i) 2.8 ;
8(d)(ii) 2.8.8 ;
8(e) cathode–hydrogen ;
anode–chlorine ;