halogens and qualitative analysis

Question 1

tend In mp bp down group

Answer 1

increase
larger molecule
more electrons
larger induced dipole dipole between molecules so more energy to break
outer shell always s2 p5 and often gain electron -1

Question 2

displacement of halogens

Answer 2

halogen that is more reactive displaces a halogen with lower reactivity
Reactivity DECREASES down group as bigger atom more shielding ,less easily attract and accept electron to form 1-

Question 3

why is chlorine more reactive than bromine

Answer 3

gains electron and forms negative ion more easily as chlorine is a smaller atom so outermost electron les shielded so electron to be gained more strongly attracted to nucluesq)
cl2 (aq) + 2Br – (aq)  2Cl – (aq) + Br2(aq)

Question 4

chlorine and water and its use

Answer 4

Cl2(g) + H2O(l)HClO(aq) + HCl (aq)
used in water treatment to kill bacteria benefits outweigh its toxic effects and risk of formation of chlorinated HC
turns red then colourless as universal indicator added

Question 5

chlorine with cold dilute NAOH

Answer 5

Cl2(aq) + 2NaOH(aq)NaCl(aq) + NaClO(aq) + H2O(l)
used as bleach to disinfect bacteria

Question 6

hot sodium hydroxide and chlorine

Answer 6

3Cl2 + 6NaOH → NaClO3 + 5NaCl + 3H2O

Question 7

testing for carbonate

Answer 7

dilute acid observe effervescent
bubble gas through limewater to test for c02 as limewater goes cloudy
HCl + Na CO 2NaCl + H O +

Question 8

testing for sulphate presence

Answer 8

acidified bacl2
white ppt forms
Ba2+ (aq) + SO42-(aq)  BaSO4 (s).

Question 9

role of nitric acid

Answer 9

react with any carbonates present to prevent formation of the precipitate Ag2CO3. This would mask the desired observations.
2 HNO3 + Na2CO3 2 NaNO3 + H2O + CO2

Question 10

Test for ammonium ion NH4+,

Answer 10

warm naoh - nh3 gas
turns litmus paper blue from red
and pungent smell