Edexcel - Chemistry Unit 2 - 4 June 2013

State two things that you would see when anhydrous calcium nitrate is heated.

Reply 1241

Original post by posthumus

I guess alkenes have a very low boiling temperature, which makes sense !

So does anyone have an image of what the apparatus should look like ? I know geor posted one yesterday :tongue:

Also is Beryllium the only one which has BeO layer, hence it can't react with water ? :smile:

If not, then why is it so unreactive

May 2010 Unit -1 Question # 18a)iii)

Instead of heating dodecane, you heat a mixture of 2-chlorobutane and alcoholic potassium hydroxide soaked in wool. Aluminium oxide is optional. :smile:

Reply 1242

GCSE-help

Original post by posthumus

Yup stick to two !!! It's four in solid form (crystals).

Can you please explain why this is? Is it something to do with the number of long pairs on the Oxygen atom or is it the fact it has two Hydrogen atoms? The MS also says HF can only form 1 hydrogen bond per molecule, so I'm guessing it's the latter reason.

Thanks.

Reply 1243

Original post by GCSE-help

Guys in the Jan 2012 MS it says Water can form 2 Hydrogen bonds per molecule, but some guys on here seem to think it's four?

Its four, two for the Lone pairs on the oxygen and one per hydrogen, hence why H20 has a much higher boiling point than H-F which only forms two hydrogen bonds per molecule

Reply 1244

posthumus

OP

20

Original post by airheadbuster

May 2010 Unit -1 Question # 18a)iii)

Instead of heating dodecane, you heat a mixture of 2-chlorobutane and alcoholic potassium hydroxide soaked in wool. Aluminium oxide is optional. :smile:

Okay thanks, but do you have an image of what the apparatus looks like ? :frown:

Original post by Linked

State two things that you would see when anhydrous calcium nitrate is heated.

Brown fumes of NO2 for sure ! Possibly bubbles of Oxygen gas. Or if CaO has a particular colour, not sure :tongue:

Reply 1245

Original post by posthumus

Okay thanks, but do you have an image of what the apparatus looks like ? :frown:

Brown fumes of NO2 for sure ! Possibly bubbles of Oxygen gas. Or if CaO has a particular colour, not sure :tongue:

Reply 1246

GCSE-help

Original post by posthumus

Yup stick to two !!! It's four in solid form (crystals).

Can you please explain why this is? Is it something to do with the number of long pairs on the Oxygen atom or is it the fact it has two Hydrogen atoms? The MS also says HF can only form 1 hydrogen bond per molecule, so I'm guessing it's the latter reason.

Thanks.

Original post by bhowland1994

Its four, two for the Lone pairs on the oxygen and one per hydrogen, hence why H20 has a much higher boiling point than H-F which only forms two hydrogen bonds per molecule

Well the mark scheme clearly says two :/

Reply 1247

DrTK278

5

does anyone want to revise ??

Reply 1248

Original post by posthumus

Okay thanks, but do you have an image of what the apparatus looks like ? :frown:

Brown fumes of NO2 for sure ! Possibly bubbles of Oxygen gas. Or if CaO has a particular colour, not sure :tongue:

Here's another better one. :tongue:

@GCSE, there are two hydrogen in a molecule of water. So, there will be two hydrogen bonding per molecule. :smile:

Reply 1249

Gnome :)

Original post by GCSE-help

Guys in the Jan 2012 MS it says Water can form 2 Hydrogen bonds per molecule, but some guys on here seem to think it's four?

One water molecule will form 2 hydrogen bonds due to the 2 lone pairs.

However, the 2 hydrogens can be involved in hydrogen bonds formed by other molecules, giving the appearance of 4 hydrogen bonds around the water molecule.

So one molecule can form 2 hydrogen bonds, but can be involved in up to 2 more.

EDIT: Not sure if it's because of the hydrogens or the lone pairs, but that's the basic idea anyway (forms 2, is involved in 2)

(edited 10 years ago)

Reply 1250

Original post by GCSE-help

Can you please explain why this is? Is it something to do with the number of long pairs on the Oxygen atom or is it the fact it has two Hydrogen atoms? The MS also says HF can only form 1 hydrogen bond per molecule, so I'm guessing it's the latter reason.

Thanks.

Well the mark scheme clearly says two :/

Then we have to go with what the MS says then ..... but the internet disagrees :P http://wiki.answers.com/Q/What_is_the_maximum_number_of_Hydrogen_bonds_a_water_molecule_can_form

Reply 1251

Original post by bhowland1994

Then we have to go with what the MS says then ..... but the internet disagrees :P http://wiki.answers.com/Q/What_is_the_maximum_number_of_Hydrogen_bonds_a_water_molecule_can_form

Don't look for the answers on the internet now. It will only confuse you. :tongue:

Reply 1252

DrTK278

5

Original post by airheadbuster

Here's another better one. :tongue:

@GCSE, there are two hydrogen in a molecule of water. So, there will be two hydrogen bonding per molecule. :smile:

SO all the alkenes produced in this reaction are gases ?

Reply 1253

Original post by Gnome :)

One water molecule will form 2 hydrogen bonds due to the 2 lone pairs.

However, the 2 hydrogens can be involved in hydrogen bonds formed by other molecules, giving the appearance of 4 hydrogen bonds around the water molecule.

So one molecule can form 2 hydrogen bonds, but can be involved in up to 2 more.

This makes sense !!!! THANK YOU :biggrin:

Reply 1254

posthumus

OP

20

Original post by airheadbuster

Here's another better one. :tongue:

@GCSE, there are two hydrogen in a molecule of water. So, there will be two hydrogen bonding per molecule. :smile:

Thank you very much :biggrin:

I think I like the second one better ! :tongue:

Original post by GCSE-help

Can you please explain why this is? Is it something to do with the number of long pairs on the Oxygen atom or is it the fact it has two Hydrogen atoms? The MS also says HF can only form 1 hydrogen bond per molecule, so I'm guessing it's the latter reason.

I just read it somewhere in the book in all honesty. But theoretically it should have 4, but in solution due to reasons such as steric hinderance I'm guessing there can only be 2. Just think of each appropriate bond pair as being able to produce 1 hydrogen bond. There are 2 O-H bonds, therefore 2 hydrogen bonds are possible. Only 1 H-F, therefore 1 hydrogen bond. Now NH3.... 3 hydrogen bonds?? Hmmm :tongue:

I'll need to check that one

Reply 1255

Original post by DrTK278

SO all the alkenes produced in this reaction are gases ?

But-1-ene is a gas at room temperature.

Reply 1256

Original post by airheadbuster

Don't look for the answers on the internet now. It will only confuse you. :tongue:

I know, i was wrong anyway i didnt realise the difference between the word forms and contains .. haha #head slap

Reply 1257

Linked