Chapter 27: Gravimetric and Combustion Analysis

If reproducibility is$\mathbf{\pm }\mathbf{0}\mathbf{.}\mathbf{5}\mathbf{}\mathbf{mg}$, product mass might have been0.1339to 0.1349 g. Find wt\% $\mathbf{Al}\mathbf{(}{\mathbf{C}}_{\mathbf{9}}{\mathbf{H}}_{\mathbf{6}}\mathbf{NO}{\mathbf{)}}_{\mathbf{3}}$if the product weighed 0.1339 g.

Why is it less desirable to wash AgCl precipitate with aqueous NaNO3 than with HNO3 solution?

A 6.234-mg sample produced 12.123 mg${\mathbf{CO}}_{\mathbf{2}}$and 2.529mg of${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$.

Find the wt%of C and H in the sample.

Why would a reprecipitation be employed in a gravimetric analysis?

Explain what is done in thermogravimetric analysis.

Explain how the quartz crystal microbalance at the opening of Chapter 2 measures small masses

An organic compound with a formula mass of 417g/molwas analyzed for ethoxyl $\mathbf{(}{\mathbf{CH}}_{\mathbf{y}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{O}\mathbf{-}\mathbf{)}$groups by the reactions

$$\begin{gathered} {\mathbf{ROCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{3}}\mathbf{+}\mathbf{HI}\mathbf{\to }\mathbf{ROH}\mathbf{+}{\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{I} \\ {\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{I}\mathbf{+}{\mathbf{Ag}}^{\mathbf{+}}\mathbf{+}{\mathbf{OH}}^{\mathbf{-}}\mathbf{\to }\mathbf{AgI}\mathbf{\left(}\mathbf{s}\mathbf{\right)}\mathbf{+}{\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH} \end{gathered}$$

A 25.42-mg sample of compound produced How many ethoxyl groups are there in each molecule?

A 0.649-g sample containing only ${\mathbf{K}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}\mathbf{(}\mathbf{FM}\mathbf{174}\mathbf{.}\mathbf{27}\mathbf{)}$and $\mathbf{\left(}{\mathbf{NH}}_{\mathbf{4}}{\mathbf{)}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}\mathbf{\right(}\mathbf{FM}\mathbf{132}\mathbf{.}\mathbf{14}\mathbf{)}$was dissolved in water and treated with$\mathbf{Ba}\mathbf{(}{\mathbf{NO}}_{\mathbf{3}}{\mathbf{)}}_{\mathbf{2}}$to precipitate all${\mathbf{SO}}_{\mathbf{4}}^{\mathbf{-}\mathbf{2}}{\mathbf{asBaSO}}_{\mathbf{4}}\mathbf{(}\mathbf{FM}\mathbf{233}\mathbf{.}\mathbf{39}\mathbf{)}$. Find the weight percent of${\mathbf{K}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$in the sample if 0.977 g of precipitate was formed.

${\mathbf{LaCoO}}_{\mathbf{3}\mathbf{+}\mathbf{x}}$, has a perovskite structure (Box 19-1) with variable oxygen content. The figure shows the thermogravimetric curve observed when 41.8724m gwere heated in role="math" localid="1665035505591" $\mathbf{5}\mathbf{}\mathbf{vol}\mathbf{\%}\mathbf{}\mathbf{}{\mathbf{H}}_{\mathbf{2}}\mathbf{}\mathbf{in}\mathbf{}\mathbf{Ar}\mathbf{.}\mathbf{La}\left(\mathrm{II}\right)$does not react, but cobalt is reduced to Co(s)

(a) What is the oxidation state of cobalt in the ideal formula ${\mathbf{LaCoO}}_{\mathbf{3}}$

(b) Write the reaction of role="math" localid="1665035588740" ${\mathbf{LaCoO}}_{\mathbf{3}}\mathbf{}\mathbf{with}\mathbf{}{\mathbf{H}}_{\mathbf{2}}$ to produce ${\mathbf{La}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}\mathbf{}\mathbf{with}\mathbf{}\left(s\right)\mathbf{,}\mathbf{Co}\left(s\right)\mathbf{,}\mathbf{and}\mathbf{}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\left(s\right)$

(c) If $\mathbf{41}\mathbf{.}\mathbf{8724}\mathbf{mg}\mathbf{}\mathbf{of}\mathbf{}{\mathbf{LaCoO}}_{\mathbf{3}}$ react completely, what will be the mass of product$\mathbf{(}{\mathbf{La}}_{\mathbf{2}}\mathbf{}{\mathbf{O}}_{\mathbf{3}}\mathbf{+}\mathbf{(}\mathbf{Co}\mathbf{)}$?

(d) Write the balanced reaction of role="math" localid="1665035782894" ${\mathbf{LaCoO}}_{\mathbf{3}\mathbf{+}\mathbf{x}}\mathbf{}\mathbf{with}\mathbf{}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}$ to produce ${\mathbf{La}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}\mathbf{,}\mathbf{Co}\mathbf{,}\mathbf{}\mathbf{and}\mathbf{}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{.}\mathbf{}\mathbf{If}\mathbf{}\mathbf{41}\mathbf{.}\mathbf{8724}\mathbf{mg}\mathbf{}\mathbf{of}\mathbf{}{\mathbf{LaCoO}}_{\mathbf{3}\mathbf{+}\mathbf{1}}$react completely; what will be the mass of solid product? Your answer will be an expression with x in it.

(e) From the observed product mass $\left(37.767\mathrm{mg}\right)\mathbf{}\mathbf{at}\mathbf{}\mathbf{700}\mathbf{°}\mathbf{c}$, find x in${\mathbf{LaCoO}}_{\mathbf{3}\mathbf{+}\mathbf{x}}$ Write the formula of the starting solid.

(f) In part (c), the mass lost from the ideal formula ${\mathbf{LaCoO}}_{\mathbf{3}\mathbf{+}\mathbf{x}}$, is 4.0877 mg. What is the product nearrole="math" localid="1665035980286" $\mathbf{500}\mathbf{°}\mathbf{C}$where the mass is -40.51 mg?