(I) Read the passage given below and answer the following questions: In spite of the predictions of stable noble gas compounds since at least 1902, unsuccessful attempts at their synthesis gave rise to the widely held opinion that noble gases are not only noble but also inert.
It was not until 1962 that this dogma was shattered when Bartlett in Canada published the first stable noble gas compound XePtF6 . This discovery triggered a worldwide frenzy in this area, and within a short time span many new xenon, radon, and krypton compounds were prepared and characterized. The recent discoveries show the ability of xenon to act as a ligand.
The discovery by Seppelt’s group that more than one xenon atom can attach itself to a metal center which in the case of gold leads to surprisingly stable Au- Xe bonds. The bonding in [AuXe4]2+ involves 4 Xe ligands attached by relatively strong bonds to a single Au(II) center in a square planar arrangement with a Xe-Au bond length of about 274 pm This discovery provides not only the first example of multiple xenon ligands but also represents the first strong metal – xenon bond.
1.Compounds of noble gases except _______ are known. a. Krypton b. Radon c. Helium d. Xenon
2. Xe is a ___________ ligand a. ambidentate b. bidantate c. unidentate d. hexadentate
Answers : 1. c 2. c
(II) Read the passage given below and answer the following questions: Boiling point or freezing point of liquid solution would be affected by the dissolved solids in the liquid phase. A soluble solid in solution has the effect of raising its boiling point and depressing its freezing point. The addition of non-volatile substances to a solvent decreases the vapor pressure and the added solute particles affect the formation of pure solvent crystals.
According to many researches the decrease in freezing point directly correlated to the concentration of solutes dissolved in the solvent. This phenomenon is expressed as freezing point depression and it is useful for several applications such as freeze concentration of liquid food and to find the molar mass of an unknown solute in the solution. Freeze concentration is a high quality liquid food concentration method where water is removed by forming ice crystals.
This is done by cooling the liquid food below the freezing point of the solution. The freezing point depression is referred as a colligative property and it is proportional to the molar concentration of the solution (m), along with vapor pressure lowering, boiling point elevation, and osmotic pressure.
These are physical characteristics of solutions that depend only on the identity of the solvent and the concentration of the solute. The characters are not depending on the solute’s identity.
1. When a non volatile solid is added to pure water it will: a. boil above 100oC and freeze above 0oC b. boil below 100oC and freeze above 0oC c. boil above 100oC and freeze below 0oC d. boil below 100oC and freeze below 0oC
2. Colligative properties are: a. dependent only on the concentration of the solute and independent of the solvent’s and solute’s identity. b. dependent only on the identity of the solute and the concentration of the solute and independent of the solvent’s identity. c. dependent on the identity of the solvent and solute and thus on the concentration of the solute. d. dependent only on the identity of the solvent and the concentration of the solute and independent of the solute’s identity.
3. Assume three samples of juices A, B and C have glucose as the only sugar present in them. The concentration of sample A, B and C are 0.1M, .5M and 0.2 M respectively. Freezing point will be highest for the fruit juice: a. A b. B c. C d. All have same freezing point
4. Identify which of the following is a colligative property : a. freezing point b. boiling point c. osmotic pressure d. all of the above
Answers : 1 (b) 2 (d) 3 (a) 4(c)
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Assesstion and reasoning