Elemental Composition Of Pure Substances
A compound is analysed and found to contain 52.14% carbon, 13.13% hydrogen, and 34.73% oxygen by mass. What is the empirical formula of this compound?
Which of the following statements best explains why the formula NaCl does not represent a discrete molecule?
Silicon dioxide (SiO₂) and carbon dioxide (CO₂) both contain two oxygen atoms per non-oxygen atom in their formulas. Which statement correctly distinguishes their structural descriptions?
A chemist analyses two samples of a compound: a 2.00 g sample prepared in a laboratory and a 500.0 g sample extracted from a natural mineral deposit. Both are confirmed to be pure. According to the law of definite proportions, which prediction is correct?
A student determines the empirical formula of a compound and obtains the mole ratio Fe : O = 1.00 : 1.33 after dividing by the smallest mole value. What should the student do next?
Three compounds — formaldehyde, acetic acid, and glucose — all share the empirical formula CH₂O. A student concludes that they must therefore have identical chemical properties. Which statement best evaluates this conclusion?
A compound is 26.57% potassium, 35.36% chromium, and 38.07% oxygen by mass. What is its empirical formula?
An unknown compound has the empirical formula CH₂O and a molar mass of 180.16 g mol⁻¹. What is its molecular formula?
A forensic chemist analyses a white powder and determines it is 39.32% sodium, 60.68% chlorine by mass. The chemist compares this to the known composition of pure NaCl (39.34% Na, 60.66% Cl). Which interpretation is most justified?
A compound contains 43.64% phosphorus and 56.36% oxygen by mass. What is its empirical formula?
A student has a sample of an unknown molecular compound with empirical formula NO₂. Without knowing the molar mass, which of the following molecular formulas can the student eliminate as impossible?
A Mars rover analyses a mineral sample and finds it contains 69.94% iron and 30.06% oxygen by mass. On Earth, the mineral magnetite (Fe₃O₄) has a known composition of 72.36% Fe and 27.64% O. What should the mission scientists conclude?
A student attempts to determine the empirical formula of a compound that is 30.45% nitrogen and 69.55% oxygen by mass. The student calculates moles: N = 2.174 mol, O = 4.347 mol. After dividing by the smallest, the student obtains the ratio N : O = 1.00 : 2.00 and reports the empirical formula as NO₂. The student’s molar mass data later reveals the compound’s molar mass is 92.02 g mol⁻¹. What is the molecular formula?
Which of the following compounds has an empirical formula that is identical to its molecular formula?
A newly synthesised pharmaceutical compound is analysed and found to have the following percent composition: 49.48% carbon, 5.19% hydrogen, 28.85% nitrogen, and 16.48% oxygen. Determine its empirical formula.