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A student attempts to identify an unknown compound by reactions to calculate mass relationships....

Question:

A student attempts to identify an unknown compound by reactions to calculate mass relationships. After heating a sample weighing 0.4107g, the mass decreased to 0.2957g. when the product was reacted to from a chloride, the resulting mass was 0.2793g. a. Is the unknown a carbonate or hydrogen carbonate? state your reason. b. given the answer to part a, the unknown is one of the what compounds? c. how many moles of chloride salt would be produced from one mole of the original unknown compound?

Molarity and Molality:

Molarity (M) is defined as the number of moles of solute per liter of solution. molarity = moles of solute/liters of solution. Molality (m) is defined as the number of moles of solute per kilogram of solvent.

molality = moles of solute/kilograms of solvent.

Answer and Explanation: 1

(A) Unknown compound is hydrogen carbonate

{eq}2 NaHCO_{3}\rightarrow Na_{2}CO_{3}+H_{2}O+CO_{2} {/eq}

(B) {eq}Na_{2}Co_{3}+2HCl\rightarrow 2Nacl+H_{2}o+co_{2} {/eq}

{eq}K_{2}CO_{3}+2HCL\rightarrow 2KCl+H_{2}o+CO_{2} {/eq}

It may be a potassium or sodium salt.

(c) One mole of chloride salt would be produced from one mole of the Original unknown compound.

experiment yield {eq}=\frac{0.2793(g)}{0.4107(g)}\times100\\ =0.68005\times100\\ =68% {/eq}

2 moles of KCl {eq}\Rightarrow 2\times74.5=149.1 {/eq} g\mole

2 moles of NaCl {eq}\Rightarrow 2\times58.5=117 {/eq}g\mol

2 moles of {eq}KHCO_{3} {/eq}{eq}\Rightarrow 2\times100=200 {/eq} g\mole

2 moles of {eq}NAHCO_{3} {/eq}{eq}\Rightarrow 2\times84=168 {/eq}

% of yield of KCl{eq}\Rightarrow \frac{149.1}{200}\times100=74.5 {/eq}%

% of yield of NaCl {eq}\Rightarrow \frac{117}{168}\times100=69.64 {/eq}%

So our given unknown compound is NAHCO_{3}


Learn more about this topic:

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Calculating Molarity and Molality Concentration

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Chapter 8 / Lesson 4
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What is molarity? What is molality? Compare molarity vs molality by viewing molality and molarity formulas, how to calculate molarity and molality, and examples.


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