Composition Of Mixtures
A student claims that sodium chloride (NaCl) is a mixture because it contains two different elements. Which statement best explains why this claim is incorrect?
Iron(III) oxide, Fe₂O₃, has a molar mass of 159.69 g mol⁻¹. What is the percent composition by mass of iron in Fe₂O₃? (Molar mass of Fe = 55.85 g mol⁻¹)
A mixture contains only CH₄ and CO₂. If additional CO₂ is added to the mixture while the amount of CH₄ remains constant, what happens to the overall percent composition by mass of carbon in the mixture?
A 5.00 g sample believed to be pure CaCO₃ undergoes elemental analysis and is found to contain 38.50% calcium by mass. The theoretical mass percent of calcium in pure CaCO₃ is 40.04%. What mass of calcium was detected in the sample, and what does this suggest?
A 10.00 g mixture contains only NaCl (M = 58.44 g mol⁻¹) and KCl (M = 74.55 g mol⁻¹). Elemental analysis reveals that the mixture contains 5.200 g of chlorine. What is the mass of NaCl in the mixture?
Which of the following correctly explains why a pure compound always has a fixed percent composition by mass?
A forensic chemist analyzes a white powder and finds it contains 39.00% sodium and 61.00% chlorine by mass. The theoretical percent composition of pure NaCl is 39.34% Na and 60.66% Cl. Which interpretation of these data is most justified?
An environmental scientist collects a water sample from a saline lake and determines that the dissolved solids are a mixture of NaCl and MgCl₂. If the proportion of MgCl₂ in the mixture increases, what happens to the overall mass percent of chlorine in the dissolved solids?
A student needs to determine the empirical formula of an unknown pure compound. Elemental analysis shows the compound is 52.14% carbon, 13.13% hydrogen, and 34.73% oxygen by mass. Which step is necessary immediately after converting mass percentages to moles of each element?
A geologist analyzes an 8.00 g mixture of MgO (M = 40.30 g mol⁻¹) and CaO (M = 56.08 g mol⁻¹) and finds it contains 2.85 g of oxygen. What is the mass of MgO in the mixture?
Two sealed containers each hold 20.0 g of white solid. Container X holds pure NaCl. Container Y holds a mixture of NaCl and KCl. A student analyzes both and finds that Container X contains 12.13 g of chlorine. Which chlorine mass in Container Y would confirm it is a mixture and not pure NaCl?
A research lab synthesizes a batch of aspirin (C₉H₈O₄, M = 180.16 g mol⁻¹) and runs elemental analysis. The theoretical mass percent of carbon in pure aspirin is 60.00%. The analysis returns a carbon mass percent of 62.5%. Which conclusion is best supported?
Calculate the mass percent of oxygen in magnesium oxide, MgO. (Molar masses: Mg = 24.31 g mol⁻¹, O = 16.00 g mol⁻¹)
A bronze alloy is a mixture of copper (Cu) and tin (Sn). A 50.0 g sample of bronze is found to contain 44.0 g of copper. If a second 50.0 g sample of bronze from a different source contains 40.0 g of copper, what does this demonstrate about the nature of bronze?
A chemist has a 12.00 g mixture of CaCO₃ (M = 100.09 g mol⁻¹) and SiO₂ (M = 60.08 g mol⁻¹). The mixture is found to contain 2.40 g of calcium. Determine the mass of CaCO₃ in the mixture. (Molar mass of Ca = 40.08 g mol⁻¹)
An atmospheric scientist studying air composition notes that air is approximately 78% N₂ and 21% O₂ by volume, with the remainder being argon and trace gases. A sample of air from a high-altitude balloon shows 75% N₂ and 24% O₂. What does this finding indicate?