Edexcel CHEMISTRY DOUBTS!!!!

[Deadly_king]

Jazaka allahu kulla kari dude for helping me out

Anytime

I just hope you understood the basic principles so that you can do such questions on your own in the future 

[The Golden Girl =D]

Anytime

I just hope you understood the basic principles so that you can do such questions on your own in the future 

I did , don't worry

[Deadly_king]

I did , don't worry

Now, I can rest in peace 

[**RoRo**]

Here's a question that our teacher gave to us on a test:

A mixture of 10cm³ methane and 10cm³ ethane has sparked with an excess of oxygen. After cooling to room temperature, the residual gas was passed through aqueous potassium hydroxide. Calculate the volume of gas absorbed by the alkali.

Any help in solving it please?

[ashish]

ok CH4 + 2O2----> CO2 + 2H2O
     10cm^3            10cm^3

C2H6 + 2.5 O2 -----> 2CO2 + 3H2O 
10cm^3                    20cm^3

in total 30 cm^3 CO2 was released which reacted with alkali         

[Deadly_king]

ok CH4 + 2O2----> CO2 + 2H2O
     10cm^3            10cm^3

C2H6 + 2.5 O2 -----> 2CO2 + 3H2O 
10cm^3                    20cm^3

in total 30 cm^3 CO2 was released which reacted with alkali         

Yeah......Ashish is right

From the 1st equation we note that :
1 mole of CH₄ burns completely on oxygen to form 1 mole of CO₂
I mole is equal to 24dm³ = 24000cm³
Therefore 24000cm³ of methane produces 24000cm³ CO₂
Hence 10 cm3 of methane will produce 10cm3 of CO₂

Same principle is applied for ethane 

Total volume absorbed : 30cm³

[The Golden Girl =D]

here is a part in the syllabus that i tried to understand but I can't seem to understand it :S

j represent data , in a graphical form , for elements 1 to 36 and use this to explain the meaning of the term " periodic property "

this is in the Chapter "atomic structure and the periodic table" --> mass spectrometer

Thank you in advance

[Deadly_king]

here is a part in the syllabus that i tried to understand but I can't seem to understand it :S

j represent data , in a graphical form , for elements 1 to 36 and use this to explain the meaning of the term " periodic property "

this is in the Chapter "atomic structure and the periodic table" --> mass spectrometer

Thank you in advance

I am not sure but I think it's talking about the different trends across a period in the periodic table.

Example : You should know the graph describing the trend of melting points across period 3. There are many graphs each describing a physical property across the period, namely atomic radius, ionic radius, electrical conductivity and first ionisation energy.

You should be able to explain the graph, that is the trend it takes from sodium to chlorine in period 3. The trends will be almost the same across each period and for the same reasons.

I can't seem to link it with mass spectrometry though

[The Golden Girl =D]

I am not sure but I think it's talking about the different trends across a period in the periodic table.

Example : You should know the graph describing the trend of melting points across period 3. There are many graphs each describing a physical property across the period, namely atomic radius, ionic radius, electrical conductivity and first ionisation energy.

You should be able to explain the graph, that is the trend it takes from sodium to chlorine in period 3. The trends will be almost the same across each period and for the same reasons.

I can't seem to link it with mass spectrometry though

Aha Okay can u give me an example so that I know what I Exactly Need to know :S

Jazaka Allahu Kulla kair

[Deadly_king]

Aha Okay can u give me an example so that I know what I Exactly Need to know :S

Jazaka Allahu Kulla kair

Ok.......i'll elaborate a bit on melting points. You may be asked to plot a graph of melting points against the different elements across the period 3. Find attached a graph, though we are not concerned about boiling points Moreover you need not provide so much detail. A sketch will be more than enough

1. Sodium, Magnesium and Aluminium are metals with strong metallic bonds. The melting point increases from Sodium to Aluminium because of stronger metallic bonds due to increase in number of electrons. Hence melting point increases accordingly.

2. Silicon has the highest melting point because a large amount of energy is required to break the strong covalent bonds holding the silicon atoms together in its giant molecular structure.

3. The other elements exist as simple molecules with weak van der Waal's forces holding the molecules together. These forces can be easily broken down leading to a low boiling point.
Among these molecules Sulfur has a slightly higher melting point because it exists as S₈ molecules with greater van der Waal's forces of attraction.

You need to know the trend across the period. Most of the time they'll either ask you to plot the graph or you're given the graph and is asked to describe the trend.

Here's a link which explains the other trends
http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top

I know it seems to be bulky..............but once you understand the principle it becomes easy

Anytime sis

[The Golden Girl =D]

Thanks Again

[Deadly_king]

Thanks Again

Rafwan ukhtii 

[The Golden Girl =D]

I don't get this part :S

http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top

Fall at Aluminium:
 
and partially screened by the 3s electrons as well as the inner electrons

[Deadly_king]

I don't get this part :S

http://www.chemguide.co.uk/inorganic/period3/elementsphys.html#top

Fall at Aluminium:
 
and partially screened by the 3s electrons as well as the inner electrons

As you must be aware Aluminium contains more electrons and the latter fills up orbitals in this order :
  s ---> p ----> d

The s-orbitals are closer to the nucleus, hence the force of attraction between the nucleus and the electrons from the s-orbitals is stronger.

The p-orbitals are next, hence hence the force of attraction between the nucleus and the electrons from the p-orbitals is stronger than those from the d-orbitals but weaker than those from the s-orbitals.

Moreover the s-orbital being inner the p-orbital acts as a barrier and this reduces the force of attraction between the nucleus and the electrons from the p-orbitals, This is the shielding effect or partially screened.

That is why Aluminium whose outermost electrons are found in p-orbitals have a lower ionisation energy than sodium and magnesium.

Hope it's clear enough

[The Golden Girl =D]

Ya so it's because of the More shielding that's caused by the P-orbital ..Nice  

Thank u D