Question

name
warm up sept 18th
be prepared for a quiz tomorrow (sept 19th friday).
coverage: stoichiometry, limiting reagent, % yield, avogadro’s number, grams to moles, moles to grams, etc.
a student has a 1 g sample of each of the following compounds: nacl, kbr, and kcl. which of the following lists the samples in order of increasing number of moles in the sample?

Explanation:

Step1: Calculate molar masses

The molar mass of $NaCl$: $M_{NaCl}=22.99 + 35.45=58.44\ g/mol$.
The molar mass of $KBr$: $M_{KBr}=39.098 + 79.904 = 119.002\ g/mol$.
The molar mass of $KCl$: $M_{KCl}=39.098+35.45 = 74.548\ g/mol$.

Step2: Use the formula $n=\frac{m}{M}$

Given $m = 1\ g$ for each compound. For $NaCl$, $n_{NaCl}=\frac{1\ g}{58.44\ g/mol}$. For $KBr$, $n_{KBr}=\frac{1\ g}{119.002\ g/mol}$. For $KCl$, $n_{KCl}=\frac{1\ g}{74.548\ g/mol}$.
Since the mass is the same ($m = 1\ g$) for all, the number of moles $n$ is inversely - proportional to the molar mass $M$. The larger the molar mass, the smaller the number of moles.

Step3: Order the number of moles

Since $M_{KBr}>M_{KCl}>M_{NaCl}$, then $n_{KBr}

Answer:

$KBr, KCl, NaCl$