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Practice each question, then open the answer or worked solution.
Which of the following correctly represents 360 g of water?
Choose the option :
(a) (i)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer is (d) (ii) and (iv)
Explanation:
Number of moles = Mass of water / Molar mass of water
Number of moles = 360g / 18g/mol
Number of moles = 20
Number of molecules = 20 x 6.022 x 1023 = 1.2044 x 1025 molecules of water
Thus, option (d) is correct.
Which of the following statements is not true about an atom?
Answer is (a) Atoms are not able to exist independently
The chemical symbol for nitrogen gas is
Answer is (b) N2
Explanation:
The chemical formula of Nitrogen is N but Nitrogen exist in molecule of two ions hence chemical symbol of Nitrogen gas is written as N2.
The chemical symbol for sodium is
Answer is (d) Na
Explanation:
Sodium word is derived from Latin word Natrium hence the chemical name of sodium is Na.
Which of the following would weigh the highest?
Answer is (c) 2 moles of CaCO3
Explanation:
The molecular mass of C₁₂H₂₂O₁₁ is = 12(12) + 22(1) + 11(16) gm = 342 gm
0.2 moles of it weigh = 0.2 x 342 gm = 68.4gm
The molar mass of CO₂ is = 12 + 2(16) gm = 44gm
2 moles of it weigh = 2 x 44 = 88gm
The molar mass of CaCO₃ weigh = 40 + 12 + 3(16) = 100gm
2 mole of it weigh = 2 x 100 gm = 200gm
Molar mass of H₂O is = 2(1) + 16 = 18gm
10 mole of it weigh = 10 x 18 gm = 180gm
Which of the following has maximum number of atoms?
Answer is (d) 18g of CH4
Explanation:
Number of atoms = Mass of substance × Number of atoms in the molecule/ Molar mass × NA
(a) 18 g of water =18 x3/18 ×NA = 3 NA
(b) 18 g of oxygen = 18 x2 /32 × NA = 1.12 NA
(c) 18 g of CO2 = 18 x3/44 × NA = 1.23 NA
(d) 18 g of CH4 =18 x5 /16 × NA = 5.63 NA
Note: NA = 6.023×1023
Which of the following contains maximum number of molecules?
Answer is (c) 1g H2
Note: NA = 6.023×1023