[abderraouf]

Im in year 10, i done chemistry, physics and doing biology now, however i want to retake chemistry to get a better grade, and the last time i did chemistry was 8 months ago, so this is all a bit of a blur for me. we're not doing chemistry in class anymore so I have to rely on my self-research / revision . I either dont know the answers to these questions, or im not 100% sure i got the answer right, anyway, these are the questions which i am stuck with.. (REMEMBER this is GCSE not A-Level)

They're all to do with elements and chemical reactions.

1) Describe a simple test you could do to see if a reaction is exothermic or endothermic. Name the piece of equipment you would use, and what would you observe when using it?

2) What colour is iodine at room temperature? ( is it dark purple? )

3) Astatine is the element at the bottom of group 7. Suggest its colour and give reasons for your answer. ( is it black? )

4) Give 2 uses of the following; Flourine, Chlorine, Bromine and Iodine.

5) What state would each halogen be in at 120 degrees celsius.

6) Can we use potassium chloride on our chips rather than sodium chloride? If so, which is better and why?

7) Can somebody tell me what is meant by

"Weak solutions of chlorine, bromine or iodine are added to solutions of potassium chloride, bromide or iodide. There is a colour chage if displacement happens, because displaced bromine or iodine turn the mixture light brown"

[BBTOTW]

1) Thermometer? If exothermic, temperature will go up and if endothermic temperature will go down.
2) Grey solid which sublimes to a purple vapour.
3) I think it is black - the colour of group 7 elements seems to get darker down the group.
4) Fluorine - compounds used in toothpaste, also in Teflon; Chlorine - used to disinfect swimming pools, bleach; Bromine - used for tests for double bonds, used in dyes; Iodine - tests for starch, antiseptic.
5) F - gas; Cl - gas; Br - gas; I - gas; At - I presume a gas as well?
6) We could possibly, don't know what it would taste like though! It is used in LoSalt, as it 'cancels out' NaCl.
7) I can't explain very well - isn't it just when you add the solution, you can tell if iodine or bromine have been displaced because of the colour change?
Hope this helps! x

[shungun]

well....pretty much everything is said...

7) well its like this chlorine is more reactive than bromine which is more reactive than iodine...so if you add Bromine to KI then the bromine will displace the iodine because its more reactive...hence iodine will be precipitated therefore there will be a colour change...
same with chlorine water and KBr or KI...bromine or iodine will be displaced respectively...

6)well we can use KCl but it will not tase good...(trust me , i have tasted KCl)...so...it would only be a good idea if you need to decrease sodium intake...then this might be a better option...(compared to nothing)


BTW...can you please not start 2 threads for the exact same questions...because i just realized you made another thread for these same questions...thanks

[jhomie]

1) Describe a simple test you could do to see if a reaction is exothermic or endothermic. Name the piece of equipment you would use, and what would you observe when using it?

Magnesium Ribbon with Hydrochloric acid in a polystyrene cup. Measure temperature before reaction and measure temperature after. Temperature rise is exothermic (which this reaction would be_

2) What colour is iodine at room temperature? ( is it dark purple? )

Yes, Dark purple, rarely blackish, but can sometimes be

3) Astatine is the element at the bottom of group 7. Suggest its colour and give reasons for your answer. ( is it black? )

Yes black as it is lower down than iodine and for group 7 it seems to go yellow/green ---> purple/black

4) Give 2 uses of the following; Flourine, Chlorine, Bromine and Iodine.

Fluorine:
-In plastics
-In toothpaste or water

Chlorine:
-Manufacture of disinfectants
-In water to make it safer

Bromine:
-Bromine water to distinguish between alkanes and alkenes
-In medicine

Iodine:
-Silver Iodide in photography
-In table salt

5) What state would each halogen be in at 120 degrees celsius.

Fluorine and Chlorine would be gas
Bromine would still be liquid
Iodine would still be solid

6) Can we use potassium chloride on our chips rather than sodium chloride? If so, which is better and why?

7) Can somebody tell me what is meant by

"Weak solutions of chlorine, bromine or iodine are added to solutions of potassium chloride, bromide or iodide. There is a colour chage if displacement happens, because displaced bromine or iodine turn the mixture light brown"

Iodine and Bromine are less reactive than chlorine and fluorine. So if chlorine or fluorine is added to a Pottasium Bromide or Iodide solution, then it will be displaced.

Fluorine is yellowish
Chlorine is greenish
Bromine is brownish/orangish
Iodine is purplish

F + KI ---> KF + I (purplish precipitate)