Hydrogen Halides

Question 1

what is formed when you mix hydrogen halides and water?

Answer 1

they dissolve in water, ionising to give H+ and X-

Question 2

what is formed when solid halide salts react with concentrated sulphuric acid?

Answer 2

white misty fumes of the hydrogen halids

Question 3

what is formed when conc H2SO4 is added to a bromide salt?

Answer 3

HBr gas, SO2 gas & pure brown bromine vapour

Question 4

what is formed when conc H2SO4 is added to an iodide salt?

Answer 4

HI gas, H2S gas and some purple vapour of iodine

Question 5

what should be used instead of conc sulphuric acid to form pure HBr or HI

Answer 5

concentrated phosphoric acid because phos. acid is not an oxidising agent so does not itself get reduced

Question 6

how does thermal stability change down group 7 & why?

Answer 6

thermal stability decreases down g7 because the strength of the H-X bond decreases

Question 7

what happens to the 4 different hydrogen halides on heating?

Answer 7

• HF & HCl are not broken down
• some HB is broken down - giving brown fumes of bromine gas
• most HI breaks down giving large quantities of purple iodine vapour

Question 8

how do the hydrogen halides act in water?

Answer 8

all hydrogen halides dissolve well in water to give aqueous solutions, HCl, HBr and HI all fully ionise when in aqueous solution so they are strong acids

Question 9

how do hydrogen halides react with ammonia?

Answer 9

all hydrogen halides react with ammonia to give ammonium salts - the ammonium salts formed as tiny white particles which look like a white cloud

Question 10

how do the 4 different hydrogen halides react with conc sulphuric acid?

Answer 10

• HF and HCl don’t react
• HBr is a powerful enough reducing agent to reduce H2SO4 to SO2
• HI is a powerful enough reducing agent to reduce H2SO4 to H2S

Question 11

why aren’t hydrogen halides collected over water?

Answer 11

HX are soluble in water, so would dissolve