[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"

Thank you guys!

[Kestrel_Lover_Sophie]

I have done my best on these questions. Please correct anyone if they are incorrect:


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?

Place the reactants in a container and put a thermometer in with them. Then watch to see the change of temperature on the thermometer and if it goes up the reaction is exothermic; if the reading goes down the reaction is endothermic.

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

Yes - it is a dark-purply solid.

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

It is black because as you go down Group 7 the elements become darker in colour.


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

Fluorine: toothpaste; added to drinking water
Chlorine: to sterilise water; to make PVC
Bromine: in solution as a test for unsaturation of hydrocarbons; disinfectant
Iodine: to disinfect wounds; as a test for starch

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

I can't say of the top of my head, sorry.

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

Yes, but it has a weak and bitter flavour so sodium chloride is better

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"

Thank you guys!

Some halogens are more reactive than others - most reactive at top of group 7 and so would displace other halogens in a compund [the similar electron configurations make this possible.] If chlorine displaces iodine in a compund the brown colour it had from the iodine will not longer be visible and it will decolourise.

[Malsy]

chlroine fr swimming pools

[Carlo08]

Bromine is used to test for Unsaturated Hydrocarbons ei Alkenes not Saturated ones.

Alkenes decolourise Bromene water which starts off orange.

I think F, Cl and Br will be gas at 120 and iodine mabe a liquid, not sure tho.

And iodine is Black/grey solid not purple!! It gives off purple vapour with h2so4 but iodine its self isnt purple!

[IChem]

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? )

Dark grey/black

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

Black

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

Fluorine: Added to toothpastes, used to make Teflon.
Chlorine: To make bleach, to make PVC (NOT to sterilise water, PURIFICATION however may be acceptable)
Bromine: As a dye, as a disinfectant
Iodine: Disinfectant, as a stain in analytical medicine.

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

All gas. (Whoever said Iodine would be liquid needs to do some revision!)

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

Err, probs not, I don't see why not, potassium and sodium are both needed by the body...however it wouldn't taste the same and sodium chloride is more readily available.

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"

Chlorine is a better oxidising agent then Bromine which is a better oxidising agent than Iodine and as such adding Chlorine to a solution containing bromide or iodide ions OXISISES those ions to their molecular form whereas the chlorine is reduced to Chloride ions.

[abderraouf]

thanks all!! (:

[Wenzel]

Originally Posted by Carlo08

Bromine is used to test for Unsaturated Hydrocarbons ei Alkenes not Saturated ones.

Alkenes decolourise Bromene water which starts off orange.

I think F, Cl and Br will be gas at 120 and iodine mabe a liquid, not sure tho.

And iodine is Black/grey solid not purple!! It gives off purple vapour with h2so4 but iodine its self isnt purple!

Iodine is a gas too. It sublimes at room temperature (i.e. goes straight from a solid to a gas).

[Carlo08]

Iodines standard state is solid at rp isnt it?

[EierVonSatan]

Originally Posted by Carlo08

Iodines standard state is solid at rp isnt it?

yup