i. The boiling points of hydrides of group 16 are in the order
a) H2O > H2Te > H2S > H2Se b) H2O > H2S > H2Se > H2He
c) H2O > H2Te > H2Se > H2S d) None of these
ii. Affinity for hydrogen decreases in the group from fluorine to iodine. What
of the halogen acids should have highest bond dissociation enthalpy?
a) HF b) HCl c) H Br d) HI
iii. If cone, of reactant 'A' is increased 10 times and rate of reaction becomes
100 times. What is order to 'A'?
a) 1 b) 2 c) 3 d) 4
iv. The half life period of first order reaction is 1386 seconds. The specific rate
constant of the reactions is.
a) 0.5x10-2
s
-1
b) 0.5x10-3
s
-1
c) 5.0x10-2
s
-1
d) 5.0x10-3
s
-1
v. The change required for the reductions of 1 mol of MnO2
-
to MnO2 is
a) 1 F b) 3 F c) 5 F d) 6 F
vi. Which of the following statement is correct?
a) E cell and of cell reaction both are extensive properties.
b) E cell and of cell reaction both are intensive properties
c) E cell is an intensive property while of cell reaction is an extensive
property.
d) E cell is an extensive property while of cell reaction is an intensive
property.
Answers
Answer:
Explanation:Oxygen is a gas at room temperature and is colorless, odorless, and tasteless. It is the most abundant element by mass in both the Earth’s crust and the human body. It is second to nitrogen as the most abundant element in the atmosphere (21%).
Oxygen has two allotropes, dioxygen (O2) and trioxygen (O3) (see in Activity 11.1). In general, O2 (or dioxygen) is the form referred to when talking about the elemental or molecular form because it is the most common form of the element. The O2 bond is very strong, and oxygen can also form strong bonds with other elements. However, compounds that contain oxygen are considered to be more thermodynamically stable than O2 itself.
Dioxygen is a colourless and odourless gas. It liquefies at 90 K (-183oC) and freezes at 55 K (-218oC). Oxygen atom has three stable isotopes: 16O, 17O and 18O. Dioxygen directly reacts with nearly all metals and non-metals except some metals (e.g., Au, Pt) and some noble gases. Its combination with other elements is often strongly exothermic which helps in sustaining the reaction. However, to initiate the reaction, some external heating is required as bond dissociation energy of oxygen-oxygen double bond is high (493.4 kJmol–1).
The other allotrope, ozone, O3, is a pale-blue poisonous gas with a strong odor. It is a very good oxidizing agent, stronger than dioxygen, and can be used as a substitute for chlorine in purifying drinking water without giving the water an odd taste. However, because of its unstable nature it disappears and leaves the water unprotected from bacteria. A layer of Ozone at very high altitude in the atmosphere is responsible for protecting the Earth’s surface from ultraviolet radiations; however, at lower altitudes it is poisoneous and becomes a major component of smog.
Destruction of the ozone layer
Human activities are rejecting in the atmosphere substances that have the capacity of destroying the ozone layer.The most destructrive substances are the chlorofluorocarbons (CFCs). That is why CFCs have been banned. We can contribute to the protection of the ozone layer by avoiding to use ozone destroying substances in our daily activities.
a. Sulphur
Sulphur occurs in native state, in volcanic lands and some sedimentary lands. Sulphur occurs as free element underground in some countries such as USA and Japan. Sulphur also occurs in many important metallic sulphides (0.05% of earth’s crust), such as lead sulfide, or galena, PbS; zinc blende, ZnS; copper pyrite, (CuFe)S2; cinnabar, HgS; stibnite, Sb2S3; and iron pyrite FeS2. It is also combined with other elements in the form of sulfates such as barite, BaSO4; celestite, SrSO4; and gypsum, CaSO4.2H2O, and it is present in the molecules of many organic substances such as
mustard, eggs, hair, proteins, oil of garlic, in petrol and coal.
Sulfur exists in a variety of forms called allotropes, which consist of several solid varieties, of which the most familiar are rhombic sulfur and monoclinic sulfur.
Rhombic sulphur (α-sulphur) (see figure in Activity 11.1)
Rhombic sulphur consists of yellow, translucent, octahedral crystals. It is stable below 96oC and it slowly changes to monoclinic at temperatures above 96oC. The temperature of 96oC is the transition temperature. It melts at 113oC. It has a density of 2.06 gcm-3
Monoclinic Sulphur (β-sulphur) (see figure in Activity 11.1)
Monoclinic Sulphur is stable above 96oC up to its melting point of 119oC. It consists of needle-shaped amber transparent crystals with density of 1.98gcm-3. Below 96oC, monoclinic sulphur changes to rhombic sulphur. This type of allotropy, in which one form changes to the other depending on the temperature, is called enantiotropy.
The most common naturally occurring allotrope, S8, cyclo-octasulphur, has a zigzag arrangement of the atoms around the ring, also called crown.
All forms of sulfur are insoluble in water, but the crystalline forms are soluble in carbon disulfide.
The most stable variety of the element is rhombic sulfur, a yellow, crystalline solid with a density of 2.06 g/cm3 at 20°C. Rhombic sulfur is slightly soluble in alcohol and ether, moderately soluble in oils and extremely soluble in carbon disulfide. When kept at temperatures above 94.5°C but below 120°C the rhombic form changes into monoclinic sulfur.
When ordinary sulfur melts, it forms a straw-colored liquid that turns darker with additional heating and then finally boils. When molten sulfur is slowly cooled, its physical properties change in accordance with the temperature, pressure, and method of crust formation.
Answer:
Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. ... Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell.