Question #ce84d

1 Answer
Oct 4, 2017

Answer:

The answer is (C) #"329 g mol"^(-1)#.

Explanation:

The idea here is that the minimum molar mass of the compound will correspond to a salt that contains #1# mole of sodium.

In other words, the minimum molar mass occurs when #1# mole of this salt contains #1# mole of sodium.

Now, let's assume that we're dealing with a sample of this salt that contains exactly #1# mole of sodium. This implies that the sample will also contain #1# mole of salt.

As you know, sodium has a molar mass of about #"23.0 g mol"^(-1)#. This means that this sample, which contains #1# mole of sodium, will contain #"23.0 g"# of sodium.

By definition, you know that the salt is #7%# by mass sodium, which means that every #"100 g"# of salt contains #"7 g"# of sodium. This implies that the mass of the sample will be

#23.0 color(red)(cancel(color(black)("g Na"))) * "100 g salt"/(7color(red)(cancel(color(black)("g Na")))) = "328.57 g salt"#

Since we've established that this sample contains #1# mole of salt, you can say that the molar mass of the salt is

#M_ ("M salt") = "328.57 g"/"1 mole" ~~ color(darkgreen)(ul(color(black)("329 g mol"^(-1))))#

This represents the minimum molar mass of the salt because it corresponds to #1# mole of sodium per mole of salt.