Some Basic Concepts in Chemistry
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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
- Dalton's Atomic theory could not explain which of the following? Answer: 4. Law of gaseous volume Key idea: Dalton's theory was about atoms combining in fixed whole-number ratios, with no concept of gas vo... 1
- A compound X contains 32% of A, 20% of B and remaining percentage of C. Then, the empirical formula of X is :(Given atomic masses of A = 64; B = 40; C = 32 u) Answer: 3. ABC₃ Key idea: empirical formula from percentage: divide by atomic mass, then by the smallest value. C% = 100 - 32 - 20 = 48. Ele... 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
- 1 gram of sodium hydroxide was treated with 25 mL of 0.75 M HCl solution, the mass of sodium hydroxide left unreacted is equal to Answer: 3. 250 mg Key idea: find the limiting reagent for NaOH+HCl→ NaCl+H₂O . NaOH: 1/40=0.025 mol = 25 mmol. HCl: 25×0.75=18.75 mmol. Left... 1
- Which amongst the following options is correct graphical representation of Boyle's Law?(1) P vs T, straight lines through origin labelled V_1, V_2, V_3 with V_1<V_2<V_3; (2) P vs V, hyperbolas labelled T_1, T_2, T_3 with T_3>T_2>T_1; (3) P vs 1/V, st… Answer: 3. P vs 1/V lines, T ₃ >T ₂ >T ₁ (graph) Key idea: Boyle's law: at constant T, P ∝ 1/V , so P plotted against 1/V is a straight line... 1