Question

Question #ce84d

Answer 1

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.