The dot at the rnd f this sentences has a mass of about one microgram assuming that black stuff is carbon calculate approximate atoms of carbon needed to make such a dot
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9)
15 gm of a compound Na
2
SO
4
. xH
2
0 contains 2.36 x 10^23 H
2
0 molecules.Find out the value of x.
10)
Aluminium carbide contains 75% of Al. Aluminium oxide contains 52.9% of Al and C0
2
contains 27.27% of C. Show that these figures illustrate the lawof reciprocal proportion.
11)
Weight of one atom of an element is 6.644 x 10^-23 g. Calculate g atom of element in 40 kg.
(IIT - 1975)
12)
O
2
is present in a litre flask at a pressure of 7.6 x 10 ^10 mm of Hg.Calculate number Of 0
2
molecules in the flask at 0C.
(IIT - 1983)
13)
It was found that 380 ml of a gas at 27C and 800 mm of Hg was weighed0.455 g. Find out molecular weight of gas
(IIT - 1975)
14)
Carbon forms two gaseous oxides. One of these oxides contain 42.8%carbon. While the other contains 27.27% carbon. Explain which of the lawsof chemical combination this data illustrates. State the law.
15)
Hydrogen and oxygen are known to form two compounds. The hydrogencontent in one of these is 5.93%. While in the other it is 11.2%. Show thatthis data illustrates the law of multiple proportion.

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Note: (^)-stands for raise to the power. (A)-angstronm
Answers-I
1.(a) 200g ; (b)27g
2. 2 x 10^-4 g-atoms ; 1 x 10^-4 g-atoms
3. 15.312Kg
4. 18cc
5. 44g
6. The no. fo oxygen atoms will be same.But A will have more no. of molecules.
7. C
6
H
12
8. 90g & O
2
is limiting agent
9. 7
11. 10^3 g-atoms
12. 2.69 x 10^10 moleclues
13. 28.02g
Note: (^)-stands for raise to the power. (A)-angstronm
Assignment Level-II
1.A complex of iron contains 45.6% iron by mass. Find out the number of ironatoms
in
5.00 gm of this complex.
2.An organic compound on analysis is found to have th-e followingcompos't'
i
ions: C = 41.4%, H=5.75%, N = 16.081% and rest is oxygen find outthe empirical formula of the Compound
.
3.An organic compound has the following percentage composition, C = 12.36%, H= 2. 13%, Br = 85%. Its vapour density is 94. Find its molecular formula.
4. A compound of carbon, hydrogen and nitrogen contains these elements in therespective ratio 9:1:3:5. Calculate the empirical formula. If the molecular weight is108, what is its molecular formula?
5. 1. 00 g of a hydrated salt contains 0.2014 g of iron, 0. 1153 g of sulphur, 0.2301g of oxygen and 0.4532 g. of water of crystrallisation find the empirical formula.(Fe = 56, S = 32, 0=16).
6. Nitrogen occurs in nature in the form of two isotopes with atomic mass 14 and15 respectively. If average atomic mass of nitrogen is 14.0067. What is thepercentage abundance of the two isotopes.
7. The relative abundance of various isotopes of silicon is as : Si - 28 = 92.23%, Si- 29 = 4.67 % Si-30 = 3. 10%. What is the average atomic mass of silicon.
8. An impure sample of sodium chloride which weighed 0.50 g gave on treatmentwith excess of silver nitrate solution, 0.90 g of silver chloride as precipitate.Calculate the percentage purity of the sample.
9.
(a) A hydrated sulphate of a divalent metal (atomic weight 24) contains 51.22%water of crystallisation. Calculate the number of molecules of water of crystalisation of the hvdrated salt.

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(b) A sample of Epsom salt, MgSO
4
. 7H
2
0 was found to contain, onanalysis, 7.32% of Mg. Calculate the percentage purity of the sample(Atomic weight H = 1, 0 = 16,Mg=24, S = 32)
(c) Which of the following compounds has the higher percentage of nitrogen. Ca(NO
3
)
2
; CaCN
2
; (NH
4
)
2
SO
4
. (H = 1 , C = 12, N = 14, 0 = 16, Ca= 40)
10. A crystalline salt is mixed with sand and gives on analysis the followingresults -, Cu = 22.905 %-, S= 11.52% 0 = 23.085%' H
2
0
=
32.463% andthe rest sand. Determine the percentage composition of the crystalline saltand deduce its molecular formula ( Cu = 53. 5, S = 32)
11. A certain compound containing only carbon and oxygen has a approximatemolecular weight of 290. On analysis it is found to contain exactly 50% by weightof each element. What is the molecular formula of the compound.
12. How many iron atoms are present in a stainless steel ball bearing having aradius of 0. 1 inch (1 inch = 2.54 cm). The stainless steel contains 85.6% Fe, byweight and has a density of 7.75 g / CC.
13. A sample of potato starch was ground in a ball mill to give a strach likemolecule of lower molecular weight. The product analysed 0.086% phosphorus. If each molecule is assumed to contain one atoi-n of phosphorus, what is themolecular weight of the material.
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