View Single Post
  #41  
Old Tuesday, November 15, 2011
Roshan wadhwani's Avatar
Roshan wadhwani Roshan wadhwani is offline
40th CTP (FSP)
Medal of Appreciation: Awarded to appreciate member's contribution on forum. (Academic and professional achievements do not make you eligible for this medal) - Issue reason: CSP Medal: Awarded to those Members of the forum who are serving CSP Officers - Issue reason: CE 2012 Merit 101
 
Join Date: Mar 2011
Location: Islamabad, MoFA
Posts: 2,322
Thanks: 482
Thanked 1,691 Times in 640 Posts
Roshan wadhwani is a glorious beacon of lightRoshan wadhwani is a glorious beacon of lightRoshan wadhwani is a glorious beacon of lightRoshan wadhwani is a glorious beacon of lightRoshan wadhwani is a glorious beacon of light
Default

DIFFERENCES FROM PAST PAPERS (2003)


1. Lava & Magma

• Magma is the molten rock material deep inside earth’s crust, while the same magma, when it finds its way to a volcano through fissures and cracks, and comes out of the mouth of the volcano, is referred to as lava.

• So magma is deep underground, while lava is the hot mixture of gases and molten rocks that comes out of the volcano.

• The most notable difference between magma and lava pertains to their location.


2. Fold & Fault

Fold:
A fold is a bend in a rock layer caused by forces within the crust of the earth. Folds usually occur in a series and look like waves in the rock.

Fault:
Rock layers can also break, in which case a fault occurs. A fault zone is where the sides of broken rock have moved relative to each other.

3. Caustic Soda and Caustic Potash

Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are both strongly alkaline, corrosive solids. As chemical re-agents, they are mostly interchangeable, although some differences exist in specific applications.

1. Chemistry in Air

o Sodium hydroxide, also known as lye or caustic soda, and potassium hydroxide, also known as caustic potash, are both white solids. They are hygroscopic, meaning they will absorb water from the air.
Sodium hydroxide will form sodium carbonate (Na₂CO₃, washing soda) by absorption of carbon dioxide (CO₂):
2 NaOH + CO₂ ' Na₂CO₃ + H₂O
Potassium hydroxide, however, will form potassium bicarbonate (KHCO₃):
KOH + CO₂ ' KHCO₃

2. Solubility
o Sodium and potassium hydroxide are strong bases. At room temperature, they exhibit almost identical solubilities in water - 111 grams of sodium hydroxide will dissolve in 100 millilitres of water vs. 110 grams of potassium hydroxide.

Applications
o Both hydroxides can be used in the saponification of fats to form soap. Soaps prepared from potassium hydroxide tend to exhibit greater solubility and are commonly referred to as "soft" soaps.

Manufacture
o Sodium and potassium hydroxides are prepared commercially by electrolysis of sodium chloride (NaCl, table salt) or potassium chloride (KCl):
2 NaCl + H₂O ' H₂ + Cl₂ + NaOH
2 KCl + H₂O ' H₂ + Cl₂ + KOH

Differences

o In many applications, potassium and sodium hydroxide can be freely interchanged. The primary difference between them is cost. In ton quantities, potassium hydroxide is about three times more expensive than sodium hydroxide.

4. SEM & TEM

SEM:
SEM involves shooting an electron beam at a specimen and observing the reactions on the specimen surface. When the electron hits a molecule on the surface, its energy is absorbed by the molecule, which in turn emits a lower amount of energy. This energy can be in the form of a secondary, less energetic electron, a photon of light, or x-rays. Differentiation between these emissions is used to produce image contrast. However, in order to produce a coherent image, the sample must often be prepared with a conductive coating or by embedding a resin for many biological samples.

TEM:
TEM acts much like a typical bright field microscope in the sense that it sends electrons through a specimen. As it propagates through the specimen, some of the electrons are scattered and some are transmitted. The transmitted electrons is passed through an objective lens and then projected onto a scintillating material which can then be recorded photographically. This requires samples to be prepared in very thin slices in order to allow transmission of the electrons through transparent sections.

OR


A SEM (scanning electron microscope) images using the electrons reflected from a specimen. A TEM (transmission electron microscope) images using the electrons that pass through it.

The image from an SEM thus looks somewhat like a normal photo (we're used to imaging using the light reflected from objects). However, a TEM image takes a bit more interpretation as we're not used to seeing images of light that's passed through things - think of silhouettes or slide projectors.
Reply With Quote
The Following 2 Users Say Thank You to Roshan wadhwani For This Useful Post:
madiha alvi (Sunday, September 08, 2013), student (Thursday, October 11, 2012)