- Organic Chemistry
- Aldehydes and Ketones
- Alkyl Halides, Alcohols and ethers
- Amines and other nitrogen compounds
- Aromatic Chemistry
- Carbohydrates, Amino acids, protein, Vitamin and Fat
- Carboxylic acids and its derivatives
- Chemistry in daily life
- General Mechanism in organic compounds
- Hydrocarbons
- Nomenclature and isomerism
217 - Chemistry Questions Answers
a carbon sample from the frame of a picture gives 7 counts of C-14 per minute per gram of carbon . if freshly cut wood gives 15.3 counts of C-14 per minute. calculate the age of frame (t½ of C-14 = 5570 yrs)
(a) 6286 yrs
(b) 5527 yrs
(c) 5570 yrs
(d) 4570 yrs
use t = 2.303/k * log(15.3/7)
k = 0.6932/t1/2
the binding energy per nucleon for C-12 is 7.68 MeV and that for C-13 is 7.47 MeV. calculate the energy required to remove a neutron from C-13
(a) 4.5MeV
(b) 45MeV
(c) 0.45MeV
(d) 0.045MeV
7.47*13-7.68*12 = 97.11-92.16 = 4.5 Mev approx
1gm of 94Pu-239 is an α-emitter with a half life of 24400 yrs. given 1g sample of this plutonium how many α-particles will it emit per second?
(a) 2.27*10^9
(b) 2.27*10^10
(c) 2.27*10^11
(d) 2.27*10^12
dn/dt = kn
so dn = (0.6932/24400*3.1*107)*(1/239)*6.023*1023*1
solve
a radioactive substance (M= 100g/mol) have t½ of 5 days. if today 0.125mg is left over what was its activity 20 days earlier?
(a) 522.8 Ci
(b) 1.93*10^7 Rd
(c) 1.93*10^13 Bq
(d) all of these
20 day means 4 half lifes so today 0.125mg means 0.125*24 = 2gm earlier
so activity dn/dt = kn
solve and convert in required units
a uranium mineral contains U-238 and Pb-206 in the ratio 4:1 by weight. Calculate the age of mineral (t½ for U-238 = 4.5 *10^9 years)
(a) 1.45*10^9 yrs
(b) 16.6*10^9 yrs
(c) 16.6*10^10 yrs
U:Pb = 4:1
taking these ratio as mass
we get the initial mass of U = 4+(1*235/208)
and present mass of U = 4
now use the first order equation of radioactivity
for an endothermic rx, higher value of energy of activation will be
(a) less than enthalpy of rx.
(b) 0
(c) more than enthalpy of rx.
(d) equal to enthalpy of rx.
(c) numerically it will be (c)
What is the volume of a gas at NTP and STP ?
question is irrelevant, amount of gas is not given
how can we find log and antilogs without the help of log and antilogs tables
there are methods but these are not good for all cases
16 kg oxygen gas expands at STP isobarically to occupy double of its original volume. The work done during the process is 244 kcal. HOW????????
W = PdV = nRdT = (16*1000/32)*(8.31/4.18)*273
now solve
What is the difference b/w metalloids & semimetals.
A metalloid is a chemical element that has properties that are in between or a mixture of those of metals and nonmetals and is consequently difficult to classify unambiguously as either a metal or a nonmetal. There is no standard definition of a metalloid, nor is there agreement as to which elements are appropriately classified as such. Despite this lack of specificity the term remains in use in chemistry literature.The six elements commonly recognised as metalloids are B, Si, Ge, As, Sb, Te
A semimetal is a material with a very small overlap between the bottom of the conduction band and the top of the valence band. A semimetal thus has no band gap and a negligible density of states at the fermi level. A metal, by contrast, has an appreciable density of states at the Fermi level because the conduction band is partially filled.