A historian discovers a nineteenth-century notebook in which...

A historian discovers a nineteenth-century notebook in which some observations, dated 1822 , on a substance thought to be a new element, were recorded. Here are some of the data recorded in the notebook: Ductile, silverwhite, metallic looking. Softer than lead. Unaffected by water. Stable in air. Melting point: $153^{\circ} \mathrm{C}$ Density: $7.3 \mathrm{~g} / \mathrm{cm}^{3} .$ Electrical conductivity: $20 \%$ that of copper. Hardness: About $1 \%$ as hard as iron. When $4.20 \mathrm{~g}$ of the unknown is heated in an excess of oxygen, $5.08 \mathrm{~g}$ of a white solid is formed. The solid could be sublimed by heating to over $800^{\circ} \mathrm{C}$. (a) Using information in the text and a handbook of chemistry, and making allowances for possible variations in numbers from current values, identify the element reported. (b) Write a balanced chemical equation for the reaction with oxygen. (c) Judging from Figure $7.2$, might this nineteenth-century investigator have been the first to discover a new element?

A historian discovers a nineteenth-century notebook in which some observations, dated 1822 , on a substance thought to be a new element, were recorded. Here are some of the data recorded in the notebook: Ductile, silverwhite, metallic looking. Softer than lead. Unaffected by water. Stable in air. Melting point: $153^{\circ} \mathrm{C}$ Density:
$7.3 \mathrm{~g} / \mathrm{cm}^{3} .$ Electrical conductivity: $20 \%$ that of copper. Hardness: About $1 \%$ as hard as iron. When $4.20 \mathrm{~g}$ of the unknown is heated in an excess of oxygen, $5.08 \mathrm{~g}$ of a white solid is formed. The solid could be sublimed by heating to over $800^{\circ} \mathrm{C}$. (a) Using information in the text and a handbook of chemistry, and making allowances for possible variations in numbers from current values, identify the element reported. (b) Write a balanced chemical equation for the reaction with oxygen. (c) Judging from Figure $7.2$, might this nineteenth-century investigator have been the first to discover a new element?

Key Concepts

Elemental Identification through Physical and Chemical Properties

This concept involves determining the identity of an element by comparing measured physical properties such as melting point, density, conductivity, and mechanical characteristics against known values. It is a crucial technique in chemistry for identifying unknown substances by matching observable experimental data with entries in chemical databases or handbooks.

Chemical Reaction Stoichiometry

Stoichiometry is the branch of chemistry dealing with the quantitative relationships of reactants and products in chemical reactions. It requires the use of mass conservation principles to balance chemical equations, ensuring that the number of atoms for each element is the same on both sides of a reaction.

Redox Reactions and Oxide Formation

This concept pertains to reactions in which a substance reacts with oxygen to form an oxide. It highlights the transformation of an element through oxidation, where electrons are transferred, leading to the formation of a compound that typically has properties such as sublimation under high temperatures.

Historical Perspectives on Scientific Discovery

Understanding the historical context of scientific discoveries involves evaluating how earlier observations and experiments contributed to the eventual identification and classification of elements. It also includes assessing claims of discovery and recognizing that measurement techniques, instrumentation, and theoretical frameworks have evolved over time, which sometimes recontextualizes pioneering work.

Transcript

00:01 This is sort of a fun problem.

00:03 We're given the following information.

00:05 A historian discovers a 19th century notebook in which some observations dated, whoops my bad, dated 1822 on a substance thought to be a new element we recorded.

00:19 Here's some of the data.

00:22 Was ductile, silver, white, metallic -looking, softer than lead, unaffected by water, stable in air, melting point 153 degrees celsius, density is 7 .3 grams per cubic centimeter.

01:42 Electrical conductivity is 20 % that of copper.

01:56 Hardness, 1 % hard as iron.

02:12 And then we're also given 1 .20 grams of the unknown reacts in air, she reacts with oxygen.

02:30 5 .08 grams of a weight solid is formed.

02:45 What else? solid was sublimed by heating over 800 degrees celsius.

03:08 So we're asked to use the information in the text and a handbook of chemistry, so i'll just say, just say sources, other sources, making possible allowances for various discrepancies, id the element.

03:44 Then we're going to write the balanced chemical equation for the reaction with oxygen.

04:10 And third, we are going to say, might the notebook investigator have found a new discovered a new element okay that's it might have been the first to discover a new element so on our first order of business here i sort of cheated a little bit and got some help and figured out that melting points would be quick and we were gonna look i decided to look around the elements around the p .b.

05:03 Issue the lead area so looking at our information we have thallium is 303 .5.

05:19 These are melting points.

05:24 Indian is 156 .1 degrees celsius.

05:33 10 is 232.

05:39 Antimony is 630 .5.

05:47 Bismith is 271 .3.

05:56 So then i saw that indian was pretty close there and i checked the density and the density given for indian was 7.

06:06 Indian was 7 .3 grams per centimeter cubed.

06:11 So i chose indian.

06:15 I didn't really need all that information but that's all i figured that one out.

06:22 I'm going to go to the next page to do my equation.

06:25 So in order to do the equation, i was given 5 .08 grams of the oxide were formed and i started with 4 .20 grams of my indium, which means i have 0 .88 grams of oxygen.

06:47 Those are my two values...

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