81. For a reaction \(A+2B\rightarrow C\), the amount of C formed by starting the reaction with 5 moles of A and 8 moles of B is
82. 100 mL of \(PH_{3}\) on heating forms P and \(H_{2}\). The volume change in the reaction is
A. an increase of 50 mL
B. an increase of 100 mL
C. an increase of 150 mL
D. a decrease of 50 mL
Answer : Option A
Explanation :
\(2PH_{3(g)}\rightarrow 2P_{(s)}+3H_{2(g)}\)
2 mL 3mL
\(\therefore \) 100 mL (?)
\(=\frac{100\times 3}{2}=150\ mL\)
\(\therefore \) Increase = 50 mL
83. An organic compound made of C, H, and N contains 20% nitrogen. Its molecular weight is (WB JEE 2009)
84. Volume occupied by one molecule of water \(\left ( d=1\ gm\ cm^{-3} \right )\) is
A. \(9\times 10^{-23}\ cm^{3}\)
B. \(6.02\times 10^{-23}\ cm^{3}\)
C. \(3\times 10^{-23}\ cm^{3}\)
D. \(5.5\times 10^{-23}\ cm^{3}\)
Answer : Option C
85. Calculate the number of moles in \(1\ m^{3}\) gas at STP.
A. 4.46
B. 44.6
C. 446
D. 4460
Answer : Option B
Explanation :
\(1\ m^{3}\) = 1000L
At STP, 22.4 L = 1 mol
\(\therefore \) 1000 L = \(\frac{1000}{22.4}\) = 44.6
86. An ore contains 1.24% of the mineral argentite \(Ag_{2}S\) by mass. How many grams of this ore would have to be processed in order to obtain 1.0 g of pure solid silver ?
A. 23.15 g
B. 69.45 g
C. 92.6 g
D. 46.3 g
Answer : Option C
Explanation :
\(Ag_{2}S\) \(Ag\)
248 g 216 g
(?) \(\therefore \) 1.0 g
= 1.148 g
\(ore\) \(Ag_{2}S\)
100 g 1.24 g
(?) \(\therefore \) 1.148 g
= 92.58 ≈ 92.6 g
87. Find the electric charge in coulomb of 9.0 gm of \(Al^{3+}\) ions.
A. \(9.6\times 10^{4}\)
B. \(6.9\times 10^{4}\)
C. \(2.9\times 10^{5}\)
D. \(4.8\times 10^{-19}\)
Answer : Option A
Explanation :
No of moles of \(Al^{3+}\) = \(\frac{9}{27}\) = 0.33
\(\therefore \) No of \(Al^{3+}\) ions = \(0.33\times 6.022\times 10^{23}\) = \(2\times 10^{23}\)
\(\therefore \) Electric charge = \(3\times 1.602\times 10^{-19}\times 2\times 10^{23}\) = \(9.6\times 10^{4}\) Coulomb
88. Which of the following is not a homogeneous mixture ?
89. Which of the following has the largest number of atoms ?
A. 0.5 g atom of Cu
B. 0.635 g of Cu
C. 0.25 moles of Cu atom
D. 1 g of Cu
Answer : Option A
90. 27 g of Al (at mass = 27) will react with oxygen equal to (IIT 1978)