A historian discovers a nineteenth-century notebook in which some observations, dated 1822, were recorded on a substance thought to be a new element. Here are some of the data recorded in the notebook: 'Ductile, silver-white, metallic looking. Softer than lead. Unaffected by water. Stable in air. Melting point: 153 °C. Density: 7.3 g>cm3. Electrical conductivity: 20% that of copper. Hardness: About 1% as hard as iron. When 4.20 g of the unknown is heated in an excess of oxygen, 5.08 g of a white solid is formed. The solid could be sublimed by heating to over 800 °C.' (a) Using information in the text and the CRC Handbook of Chemistry and Physics, and making allowances for possible variations in numbers from current values, identify the element reported.
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Identify the physical properties of the unknown element: ductile, silver-white, metallic, softer than lead, unaffected by water, stable in air, melting point of 153 °C, density of 7.3 g/cm³, electrical conductivity 20% of copper, hardness 1% of iron.
Compare these properties with known elements from the CRC Handbook of Chemistry and Physics, focusing on elements with similar melting points, densities, and conductivity.
Consider the chemical reaction: 4.20 g of the unknown element reacts with oxygen to form 5.08 g of a white solid. Calculate the mass of oxygen that reacted by subtracting the mass of the unknown from the mass of the product.
Determine the molar mass of the unknown element by using the mass of the unknown and the mass of oxygen to find the empirical formula of the oxide formed.
Cross-reference the calculated molar mass and empirical formula with known elements to identify the element that matches the properties and reaction data.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Physical Properties of Metals
The observations recorded in the notebook describe several physical properties of the unknown element, such as ductility, density, and melting point. Metals typically exhibit high electrical conductivity, malleability, and a shiny appearance. Understanding these properties helps in identifying the element, as they can be compared to known metals to narrow down possibilities.
The reaction of the unknown element with oxygen, resulting in a white solid, indicates its chemical reactivity. The formation of a solid product upon heating in excess oxygen suggests that the element may form an oxide. Analyzing the mass change during the reaction can provide insights into the element's identity and its oxidation state.
Density is a critical physical property used to identify elements. The recorded density of 7.3 g/cm³ can be compared to known densities of metals to help pinpoint the unknown element. Since density is a characteristic property, it can significantly narrow down the list of potential candidates when combined with other observed properties.
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