# 215 - Chemistry Questions Answers

THE PYKNOMETRIC DENSITY OF NaClis 2.165X 10-3 wHILE ITS Xray density  IS 2.178X103 kgm-3 the fraction of unoccupied sites in NaCl crystal is?ans) 5.96x 10-3.   how we will caculate this fraction

Joshi sir comment

Pyknometer is a device to measure density of substance. Density measured by pyknometer is called pyknometric density. In porous solids this density may be different from true density of solid if the liquid used is unable to fill the pores of solid.

I think that the first density will be 2.165 * 103

difference of density = 2178-2165 = 13 kg/m3

so fraction of unoccupied site = 13/2178 =  5.96 * 10-3

CRYSTALLINE  SOLIDS HAVE

a) SHORT RANGE  ORDER

b) ANISOTROPIC DISTRIBUTn

c) LONG RANGE ORDER

D)  NO ORDER

AIIMS2001

SIR AS WE KNOW THAT BOTH THE OPTION B) & C) ARE CORRECT BUT IN THIS QUES WHICH OPTn WOULD BE MORE APPROPRIATE FOR CORRET ANS

.

Joshi sir comment

According to me it should be b

for anisotropic character is a basic property of crystalline solids

Trick to remember al elements of inner transition
Joshi sir comment

remember these elements by dividing these two lines in the pairs of 7-7

## what resion  behind  tritium is B- emmiter ..??  where B- is beeta with negative sign

Joshi sir comment

1H3 ----------->  2He3-1β0

so by this equation it is clear that by emitting beta particle tritrium will be converted to more stable helium

## sir, what is the basiq  principle of  'hydrogen econmy' ???  plese write a small topic on it.

Joshi sir comment

The hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors(GM) Technical Center.

Hydrogen advocates promote hydrogen as a potential fuel for motive power (including cars and boats), the energy needs of buildings and portable electronics. Free hydrogen does not occur naturally in quantity, and thus must be generated from some other energy source by steam reformation of natural gas or another method. Hydrogen is thus an energy carrier (like a battery), not a primary energy source (like coal). The feasibility of a hydrogen economy depends on issues of energy sourcing, including fossil fuel use, climate change, and sustainable energy generation.

## Rationale

A hydrogen economy is proposed to solve some of the negative effects of using hydrocarbon fuels where the carbon is released to the atmosphere. Modern interest in the hydrogen economy can generally be traced to a 1970 technical report by Lawrence W. Jones of theUniversity of Michigan.

In the current hydrocarbon economy, transportation is fueled primarily by petroleum. Burning of hydrocarbon fuels emits carbon dioxideand other pollutants. The supply of economically usable hydrocarbon resources in the world is limited, and the demand for hydrocarbon fuels is increasing, particularly in ChinaIndia, and other developing countries.

Proponents of a world-scale hydrogen economy argue that hydrogen can be an environmentally cleaner source of energy to end-users, particularly in transportation applications, without release of pollutants (such as particulate matter) or carbon dioxide at the point of end use. A 2004 analysis asserted that "most of the hydrogen supply chain pathways would release significantly less carbon dioxide into the atmosphere than would gasoline used in hybrid electric vehicles" and that significant reductions in carbon dioxide emissions would be possible if carbon capture or carbon sequestration methods were utilized at the site of energy or hydrogen production.

Hydrogen has a high energy density by weight. An Otto cycle internal-combustion engine running on hydrogen is said to have a maximum efficiency of about 38%, 8% higher than a gasoline internal-combustion engine.

The combination of the fuel cell and electric motor is 2-3 times more efficient than an internal-combustion engine. However, the high capital costs of fuel cells, about $5,500/kW in 2002, are one of the major obstacles of its development, meaning that the fuel cell is only technically, but not economically, more efficient than an internal-combustion engine. Other technical obstacles include hydrogen storage issues and the purity requirement of hydrogen used in fuel cells – with current technology, an operating fuel cell requires the purity of hydrogen to be as high as 99.999%. On the other hand, hydrogen engine conversion technology is more economical than fuel cells. ## Perspective: current hydrogen market (current hydrogen economy)There are two primary uses for hydrogen today. About half is used in the Haber process to produce ammonia (NH3), which is then used directly or indirectly as fertilizer. Because both the world population and the intensive agriculture used to support it are growing, ammonia demand is growing. The other half of current hydrogen production is used to convert heavy petroleum sources into lighter fractions suitable for use as fuels. This latter process is known as hydrocracking. Hydrocracking represents an even larger growth area, since rising oil prices encourage oil companies to extract poorer source material, such as tar sands and oil shale. The scale economies inherent in large-scale oil refining and fertilizer manufacture make possible on-site production and "captive" use. Smaller quantities of "merchant" hydrogen are manufactured and delivered to end users as well.Hydrogen production is a large and growing industry. Globally, some 50 million metric tons of hydrogen, equal to about 170 million tons of oil equivalent, were produced in 2004. The growth rate is around 10% per year. Within the United States, 2004 production was about 11 million metric tons (MMT), an average power flow of 48 gigawatts. (For comparison, the average electric production in 2003 was some 442 gigawatts.) As of 2005, the economic value of all hydrogen produced worldwide is about$135 billion per year.

If energy for hydrogen production were available (from wind, solar, fission or fusion nuclear power etc.), use of the substance for hydrocarbon synfuel production could expand captive use of hydrogen by a factor of 5 to 10. Present U.S. use of hydrogen for hydrocracking is roughly 4 million metric tons per year (4 MMT/yr). It is estimated that 37.7 MMT/yr of hydrogen would be sufficient to convert enough domestic coal to liquid fuels to end U.S. dependence on foreign oil importation, and less than half this figure to end dependence on Middle East oil. Coal liquefaction would present significantly worse emissions of carbon dioxide than does the current system of burning fossil petroleum, but it would eliminate the political and economic vulnerabilities inherent in oil importation.

Currently, global hydrogen production is 48% from natural gas, 30% from oil, and 18% from coal; water electrolysis accounts for only 4%.[12] The distribution of production reflects the effects of thermodynamic constraints on economic choices: of the four methods for obtaining hydrogen, partial combustion of natural gas in a NGCC (natural gas combined cycle) power plant offers the most efficient chemical pathway and the greatest off-take of usable heat energy.

The large market and sharply rising prices in fossil fuels have also stimulated great interest in alternate, cheaper means of hydrogen production. As of 2002, most hydrogen is produced on site and the cost is approximately $0.32/lb and, if not produced on site, the cost of liquid hydrogen is about$1.00/lb to \$1.40/lb.

## when ortho boric acid is treated with  H2O2.  product is  ...?  answer is monoperoxoboric acid.  explain plese........

Joshi sir comment

H3BO3 + H2O2 -------->  HBO3 + 2H2O

## Na2  [B4O5(OH)4].8H2Oreacts with HCl  forms X and X is heated forms Y  and y react with Na forms Z  ...   determine  Z  ?    answer is B ( where B is boron ) plese write mechanism.......

Joshi sir comment

Borax + HCl --------------> H3BO3  + NaCl   + H2O

H3BO3  ----------------Heated---------->   B2O3   +   H2O

B2O3  +  Na   ---------------->    B  +  Na2O

## (1) The same number of atoms as in B , (2) same weight of gasas in B , (3) dubble the number of atoms asin  A  (4)half of the  number of atoms in A , ?

Asked By: SHUBHAM VED Solved By: NIKHIL VARSHNEY
Joshi sir comment

Iodoform test is used for-

a) starch

b) maltose

c) glucose

d) sucrose

MANIPAL 2012

Joshi sir comment

starch turns iodine blue

Q IN THAT Fe QUES ANSWER GIVEN IS -VE 0.405 BUT ACC. TO THIS METHOD ANSWER DO NOT MATCH

Q I STILL DIDNOT  UNDERSTAND  CO & CO2 RELATION

Joshi sir comment

Fe                ----->  Fe++  + 2e-

so E for the new reaction = [1F(0.77) + 3F(0.04)]/2F = 0.89/2 = 0.445

so it will be -0.445 for the reverse, you are asking for reduction and i submitted the answer for oxidation so the duality created.

according to the given reaction we get 2L monooxide by 1L dioxide,

initially litres of CO2  = x so it will form 2x litres of CO

and 1-x litres CO are present from the start so total litres of CO = 2x+1-x = 1+x