Atomic and molecular masses, mole concept, molar mass
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See all →- Among the following, choose the ones with equal number of atoms.A. 212 g of Na_2CO_3 (s) [molar mass = 106 g]B. 248 g of Na_2O (s) [molar mass = 62 g]C. 240 g of NaOH (s) [molar mass = 40 g]D. 12 g of H_2 (g) [molar mass = 2 g]E. 220 g of CO_2(g) [mo… Answer: 2. A, B, and D only Key idea: number of atoms = moles × atoms per formula unit × N_A . A: 212 g = 2 mol × 6 = 12 mol atoms. B: 248 g... 1
- The highest number of helium atoms is in Answer: 2. 4 mol of helium Key idea: convert each to number of atoms (He is monoatomic). 2.271098 L at STP (22.7 L/mol): 0.1 mol. 4 mol: 4 m... 1
- A 10.0 L flask contains 64 g of oxygen at 27°C. (Assume O_2 gas is behaving ideally). The pressure inside the flask in bar is(Given R = 0.0831 L bar K^-1 mol^-1) Answer: 1. 4.9 Key idea: use PV=nRT . n=64/32=2 mol, T=300 K. P=nRT/V=2×0.0831×300/10=4.986≈4.9 bar (nearest option is 4.9; 4.986 bar is 4.9... 1
- Copper crystallises in fcc unit cell with cell edge length of 3.608 × 10^-8 cm. The density of copper is 8.92 g cm^-3. Calculate the atomic mass of copper. Answer: 2. 63.1 u Key idea: density ρ=ZM/a³N_A , so M=ρ a³N_A/Z . fcc has Z = 4. a³=(3.608×10⁻⁸)³=4.697×10⁻²³\ cm³ . M=dfrac8.92×4.697×10⁻²³... 1
- Which one is not correct mathematical equation for Dalton's Law of partial pressure ? Here p = total pressure of gaseous mixture Answer: 1. p_i = chi_i p_i^° , where chi_i = mole fraction of i^th gas in gaseous mixture, p_i^° = pressure of i^th gas in pure state Key id... 1
- Tritium, a radioactive isotope of hydrogen, emits which of the following particles ? Answer: 1. Beta ( β^- ) Key idea: tritium ( ³₁H ) is a beta emitter. ³₁H→³₂He+β^-+barν : a neutron changes into a proton, emitting a β^- par... 1