You and a partner are asked to complete a lab entitled...

You and a partner are asked to complete a lab entitled "Oxides of Ruthenium" that is scheduled to extend over two lab periods. The first lab, which is to be completed by your partner, is devoted to carrying out compositional analysis. In the second lab, you are to determine melting points. Upon going to lab you find two unlabeled vials, one containing a soft yellow substance and the other a black powder. You also find the following notes in your partner's notebook-Compound 1: $76.0 \%$ Ru and $24.0 \%$ O (by mass), Compound 2: $61.2 \%$ Ru and $38.8 \% \mathrm{O}$ (by mass). (a) What is the empirical formula for Compound $1 ?$ (b) What is the empirical formula for Compound 2? (c) Upon determining the melting points of these two compounds, you find that the yellow compound melts at $25^{\circ} \mathrm{C}$, while the black powder does not melt up to the maximum temperature of your apparatus, $1200^{\circ} \mathrm{C}$. What is the identity of the yellow compound? What is the identity of the black compound? Be sure to use the appropriate naming convention depending upon whether the compound is better described as a molecular or ionic compound.

You and a partner are asked to complete a lab entitled "Oxides of Ruthenium" that is scheduled to extend over two lab periods. The first lab, which is to be completed by your partner, is devoted to carrying out compositional analysis. In the second lab, you are to determine melting points. Upon going to lab you find two unlabeled vials, one containing a soft yellow substance and the other a black powder. You also find the following notes in your partner's notebook-Compound 1: $76.0 \%$ Ru and $24.0 \%$ O (by mass), Compound 2: $61.2 \%$ Ru and $38.8 \% \mathrm{O}$ (by mass).
(a) What is the empirical formula for Compound $1 ?$
(b) What is the empirical formula for Compound 2?
(c) Upon determining the melting points of these two compounds, you find that the yellow compound melts at $25^{\circ} \mathrm{C}$, while the black powder does not melt up to the maximum temperature of your apparatus, $1200^{\circ} \mathrm{C}$. What is the identity of the yellow compound? What is the identity of the black compound? Be sure to use the appropriate naming convention depending upon whether the compound is better described as a molecular or ionic compound.

Key Concepts

Ionic vs Molecular Compound Nomenclature

The nomenclature of compounds depends on their bonding nature. Ionic compounds, typically formed between metals and nonmetals, are named using systematic rules that denote the ions involved, while molecular compounds, usually composed of nonmetals, are named with prefixes indicating the number of atoms. This differentiation is vital for clear communication and accurate description of chemical substances in the scientific community.

Physical Properties and Melting Point Analysis

Using physical properties, such as melting points, is a key method in identifying and characterizing compounds. The melting point not only indicates a compound’s thermal stability but also supports the identification of a compound by revealing differences in bonding type and structural integrity, which are especially useful when distinguishing between molecular substances and ionic solids.

Empirical Formula Determination

This concept involves converting the percentage composition by mass of each element in a compound into moles, and then finding the simplest whole-number ratio of these moles. It is a fundamental aspect in analytical chemistry that helps establish the basic composition of a compound from experimental data, which is essential for further chemical characterization and synthesis.

Percent Composition Analysis

Percent composition analysis is the process of determining the mass percentages of each element present in a compound. This technique is critical in both analytical and inorganic chemistry as it provides the data necessary for deriving empirical formulas, assessing purity, and verifying the composition of substances in a laboratory setting.

Transcript

00:01 This problem wasn't very hard, but it did take a little bit of time.

00:05 Okay.

00:06 So in this problem, you and a lab partner are doing a two -day lab.

00:21 Day one is compositional analysis.

00:35 And day two is melting points.

00:48 You are doing day two.

00:51 Your lab partner does day one.

00:53 So on day two, you go into the lab and you find in your lab drawer or your lab box, two unlabeled vials.

01:13 One vial is a yellow substance, and the other substance is a black powder.

01:37 I'll go back to this.

01:38 You find a note that tells you the compositional analysis.

01:42 You do your melting point, and you find that the melting point for the soft yellow substance is about 25 degrees celsius, and you find that your black powder doesn't melt at all.

01:58 So your apparatus goes up to 1 ,200 degrees and it doesn't melt.

02:05 Your melting point is somewhere greater than 1 ,200 degrees, which indicates that this substance is either ionic or a network solid.

02:20 Those are the only substances that have melting points that high.

02:25 This is most likely molecular.

02:35 Okay.

02:35 Now, so this is a bunch of the information that's given.

02:43 You are also told that compound one, this will be compound one, but we don't know which is which.

02:50 Sorry.

02:52 Compound one has the composition of 70%, 76 .0 % ruthenium and 24 .0 % oxygen.

03:16 Your second substance has a composition of 61 .2 % ruthenium and 38 .8 % oxygen.

03:35 For both of these, you are asked to find the empirical formula.

03:41 So the empirical formula.

03:47 The empirical formula is found by changing percent to mass, which will just be like changing percent to grams, and we'll make the assumption that this is a 100 gram sample for all of these...

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