Edexcel CHEMISTRY DOUBTS!!!!

[Deadly_king]

  b) Compare and explain the conduction of electricity by sodium chloride and copper in terms of structure and bonding. [6 marks]

i) Sodium chloride conducts electricity in the aqueous form only since it is made up of a compact ionic lattice which gives rise to crystals. In water, however, it dissolves to form Na⁺ and Cl^- ions.

It is these ions which enable sodium chloride to conduct electricity.

ii) Copper is a metal which is composed of Cu atoms in a sea of electrons. They have a strong compact shape due to the strong metallic bonds which exist between the atoms. This also gives rise to a high melting point.

The sea of electrons is formed since each copper atom have 2 electrons in their outermost shell. They are free and mobile. Hence they are able to move from one end to the other but they remain within the metal itself. These electrons are responsible for the ability of copper or any other metal to conduct electricity.

I guess this should be enough to score 6 marks but if you want to know more, try this :
http://www.newton.dep.anl.gov/askasci/phy00/phy00697.htm

http://en.wikipedia.org/wiki/Copper#Electrical_properties

4. Give 5 advantages of alloys. [5 marks]

An alloy is a metal composed of more than one element.
Since it has not mentioned any alloy in particular, your answer can vary to a very large extent.

Advantages of alloys
1. Alloys do not rust. (Example : stainless steel)

2. They are stronger. (Example : steel)

3. They are harder and more resistant. (Example : Aluminium alloy used for making cans)

4. They can be cheaper. (Example : Materials composed of aluminium or silver only is much more expensive than their alloys)

5. Alloys give the possibility to construct a material according to the need. The best alloy to make a bicylce frame need to be strong, corrosion-resistant and beautiful to watch. One metal alone would not be able to provide all these characteristics. Here an alloy would be ideal.


If you have some time, take a look here.
http://www.tutorvista.com/topic/advantages-of-alloys-over-pure-metals

http://www.engr.sjsu.edu/WofMatE/Metals&Alloys.htm

[The Golden Girl =D]

No.......you were not being stupid. Actually I need to apologise since my words were quite offensive

Sorry again

Anyway seems you understood the trend of melting point across period 3 well
That was a 5 star explanation

No worries...............i'll take on the rest

Believe they weren't

no problem bro

YESH ....

okay

[Deadly_king]

2. State the type of structure and the nature of the bonding in each of the following elements: [6 marks]
 i) aluminium
 ii) silicon
 iii) chlorine

I think GG already stated the  nature of bonding. I would just like to add some more

You must first observe that all three of the (aluminium, silicon and chlorine) are in period 3.

As we move from sodium to argon across period 3, the ionic characteristics of the element decreases while their covalent characteristics increase. This is noted by the metallic bonds in sodium and the covalent bonds in chlorine.

However aluminium, despite being a metal also has the characteristics of covalent compounds. Al₂Cl₆ is covalent.

Type of structure refers to how they exist in nature.
Aluminium usually exists in its ore bauxite.
Silicon exists as a giant molecular structure while chlorine as a simple molecular structure.

3. a) Using sodium chloride, hydrogen chloride and copper, explain what is meant by covalent, ionic and metallic bonding. [9 marks]

i) Sodium chloride is an ionic compound consisting of ions; Na⁺ and Cl^-. The ios have resulted as one electron from sodium has been transferred to chlorine so that both may acquire stable electronic configuration, i.e their outermost shell gets filled.

ii) Hydrogen chloride is on the contrary a covalent compound since hydrogen does not have the capacity to give electrons. So both the hydrogen and chlorine molecule each share one electron such that they end up with a stable electronic configuration,i.e their outermost shell gets filled.

iii) Copper has a metallic lattice composed of copper ions in a sea of electrons. There exist a strong intermolecular force of attraction between the Cu²⁺ ions and the free delocalised electrons. Hence this gives rise to the compact shape of copper.

This might help you have any doubt :
http://www.beyondbooks.com/psc92/3.asp

Hope it helped

[Deadly_king]

Believe they weren't

no problem bro

YESH ....

okay

*Glad and reassured*

[**RoRo**]

I think GG already stated the  nature of bonding. I would just like to add some more

You must first observe that all three of the (aluminium, silicon and chlorine) are in period 3.

As we move from sodium to argon across period 3, the ionic characteristics of the element decreases while their covalent characteristics increase. This is noted by the metallic bonds in sodium and the covalent bonds in chlorine.

However aluminium, despite being a metal also has the characteristics of covalent compounds. Al₂Cl₆ is covalent.

Type of structure refers to how they exist in nature.
Aluminium usually exists in its ore bauxite.
Silicon exists as a giant molecular structure while chlorine as a simple molecular structure.

i) Sodium chloride is an ionic compound consisting of ions; Na⁺ and Cl^-. The ios have resulted as one electron from sodium has been transferred to chlorine so that both may acquire stable electronic configuration, i.e their outermost shell gets filled.

ii) Hydrogen chloride is on the contrary a covalent compound since hydrogen does not have the capacity to give electrons. So both the hydrogen and chlorine molecule each share one electron such that they end up with a stable electronic configuration,i.e their outermost shell gets filled.

iii) Copper has a metallic lattice composed of copper ions in a sea of electrons. There exist a strong intermolecular force of attraction between the Cu²⁺ ions and the free delocalised electrons. Hence this gives rise to the compact shape of copper.

This might help you have any doubt :
http://www.beyondbooks.com/psc92/3.asp

Hope it helped

Deadly_king, you're a life-saver!

Thank you so much for your help, I really appreciate it!

A question, are you a student? if yes, what subjects are you doing now?

[Deadly_king]

Deadly_king, you're a life-saver!

Thank you so much for your help, I really appreciate it!

A question, are you a student? if yes, what subjects are you doing now?

No problem dude

Anytime

Yeah........am doing Chemistry, Physics and Maths for A2 and Bio and GP for AS. Currently in exams

What about you
It seems you are new here

[**RoRo**]

WOW!
I'm doing a full A-level in Math, an AS in Chem and Bio - that's it!!

Good luck for your exams!! I'm sure you'll do great!

I was here last year but in the IGCSE thread, now I moved on to AS & A2!!

& seriously, you guys are so helpful!

Okay, one more question:
 
Phosphorus and Sulphur exist as molecules of P₄ and S₈, respectively. Explain their difference in melting temperatures. [For P it is 317K and for S it is 386K]

I don't know how to word out my answers, I mean I understand why, but I don't know how to write it down or what exactly to write down! :/

[Deadly_king]

WOW!
I'm doing a full A-level in Math, an AS in Chem and Bio - that's it!!

Good luck for your exams!! I'm sure you'll do great!

I was here last year but in the IGCSE thread, now I moved on to AS & A2!!

& seriously, you guys are so helpful!

Okay, one more question:
 
Phosphorus and Sulphur exist as molecules of P₄ and S₈, respectively. Explain their difference in melting temperatures. [For P it is 317K and for S it is 386K]

I don't know how to word out my answers, I mean I understand why, but I don't know how to write it down or what exactly to write down! :/

I really hope so

The slight difference is the result of the size of the molecules. Phosphorus exists as P₄ which is smaller than S₈. hence it has less Van Der Waal's forces of attraction between the molecules. This is why it has a lower melting point.

This may be useful :
http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top

Scroll down a bit to reach melting points

[**RoRo**]

I really hope so

The slight difference is the result of the size of the molecules. Phosphorus exists as P₄ which is smaller than S₈. hence it has less Van Der Waal's forces of attraction between the molecules. This is why it has a lower melting point.

This may be useful :
http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top

Scroll down a bit to reach melting points

Thanks a lot, the link was really useful, it answered a couple more questions in mind!

[Deadly_king]

Thanks a lot, the link was really useful, it answered a couple more questions in mind!

Anytime mate

Glad it cleared your doubts

[**RoRo**]

Another set of questions again!!

1. Why is diamond shiny?

2. Why does PCl₃ form a stable compound with BCl₃?

3. Urea (NH₂)₂C=O is commonly used as a fertiliser in most of Europe, whereas ionic ammonium nitrate NH₄NO₃is the most popular fertiliser in the UK.
Suggest 2 advantages of using urea as a fertilizer compared with ammonium nitrate.

4. Graphite fibres are often used for the brushes [contacts] in electric motors.
i) Give two reasons why graphite fibres are used this way.

ii) Give three reasons why diamonds would be unsuitable for this use.

THANKS A LOT IN ADVANCE!!

[Deadly_king]

4. Graphite fibres are often used for the brushes [contacts] in electric motors.
i) Give two reasons why graphite fibres are used this way.

ii) Give three reasons why diamonds would be unsuitable for this use.

i) 1. Graphite is a very good conductor of electricity since it has free mobile electrons within its structure.
   2. Graphite is made up of carbon which is very common in our daily life. Hence it is readily available.

ii) 1. Diamond is a very bad conductor of electricity since it does not have free delocalised electrons as the carbon atoms are all bonded to four other carbon atoms.
   2. Diamond is a very expensive material due to its beauty and use in jewelleries have increased its value.
   3. Diamond is one of the hardest substance known on Earth. Moreover it is shiny which makes it a worse radiator of heat.

I'll work out the rest asap

[Uchia]

could anyone help me in question 2 page 49 of the edexcel A2 book and thanks

part a only

[Deadly_king]

1. Why is diamond shiny?

I don't think you need to know that, buddy I had to carry out some research before finding this :

There are 3 properties of a diamond in relation to light :

1. Brilliance : the light reflections caused by the white light that enters the diamond bouncing off its facets inside and exiting the diamond AND also the light that reflects from its surface

2.Fire : the flashes of color, like a rainbow of colors, that you can see in a polished diamond when you move the stone or when you or the light moves. The different colors that make up together the white light that enter the stone are faster or slower than others. When the get reflected inside the gem by its facets and exits the stone, there is a difference in angle between these color rays so you can see separate colors. This creates fire, and it is because of the unique refractive quality diamond has.

3. Scintillation : the flashes of light and the contrasting areas you see when the diamond, the light or the observer moves.

Try not be so curious about things outside the syllabus

2. Why does PCl₃ form a stable compound with BCl₃?

Such a compound would be theoretically stable because PCl₃ has a free lone pair of electrons, while BCl₃ is missing a pair of electrons. The lone pair on PCl₃ can coordinate to the empty space on BCl₃, giving all the atoms an octet.

Hence a coordinate covalent bond is formed between the two molecules to form a rather stable compound which is however quite rare

3. Urea (NH₂)₂C=O is commonly used as a fertiliser in most of Europe, whereas ionic ammonium nitrate NH₄NO₃is the most popular fertiliser in the UK.
Suggest 2 advantages of using urea as a fertilizer compared with ammonium nitrate.

1. Urea is readily available through excrements of most organisms. Hence it is cheaper.
2. The yield is extremely high and it has no side-effects on any plants.

If you have time check these :
http://ezinearticles.com/?Beneficial-Uses-of-the-Urea-Fertilizer&id=5229780

http://www.extension.umn.edu/distribution/cropsystems/dc0636.html

Hope it helps

[Deadly_king]

could anyone help me in question 2 page 49 of the edexcel A2 book and thanks

part a only

Hmm............actually I don't have the book right now.

Would you mind to post the question