<ol>
<li>A compound found in cast iron is cementite, which contains iron and carbon. A 3.113 g sample of cementite was heated in air, producing 4.153 g of Fe2O3. The CO2 gas, another reaction product, escaped. What is the empirical formula of cementite?
Answer: Fe3C</li>
<li>Reaction of rhenium metal with Re2O7 gives a solid of metallic appearance which conducts electricity almost as well as copper. A .788 g sample of this material, which contains only rhenium and oxygen was oxidized in an acidic solution of hydrogen peroxide. Addition of an excess of KOH gave .973 g of KReO4. What is the equation for the reaction of Re with Re2O7?
Answer: Re + Re2O7 -> 7ReO3</li>
<li>A 25 mL volume of .100 M H2Cr2O7 was added to 75 mL of .100 M H2FeCl4. The reaction is as follow: H2Cr2O7 + 6H2FeCl4 -> 2(Cr(H20)6)Cl3 + 6FeCl3 What mass of (Cr(H20)6)Cl3 was produced?
Answer: .66 g</li>
</ol>
<p>Please provide explanations! </p>
<p>I’ll explain #3 since it looks the most straightforward, not sure if I’ll get to the others. This is written with the expectation that you have taken a previous chemistry course and are familiar with the terminology and calculation processes. If there is anything that is unclear, please don’t hesitate to ask.</p>
<p>First use the given quantities and the equation Molarity=moles/liters to calculate the number of moles for both the reactants (ie for H2Cr2O7 do .1M=moles/.025L and solve for moles) </p>
<p>Remember to convert milliliters to liters when doing this.</p>
<p>After this is done, you must determine the limiting reactant. There’s a couple methods to do this, so I’ll use the one that makes the most sense intuitively (though there is a shorter method, depending on what the question asks. </p>
<p>Use stoichiometry to determine how many moles of (Cr(H20)6)Cl3 is produced from each reactant. (for H2Cr2O7 do mol H2Cr2O7*(2 mol (Cr(H20)6)Cl3/1 mol H2Cr2O7)</p>
<p>After you have determined how much product each reactant creates, take the smaller amount, as that is how much product can be created before one of the reactants is completely consumed.</p>
<p>Then convert the quantity of (Cr(H20)6)Cl3 from moles to grams</p>