Question #24c67

1 Answer
Jun 27, 2015

That much sodium nitrate contains #1.4 * 10^(22)# formula units.


Since sodium nitrate is an ionic compound, you can't really say that you're dealing with molecules, but with formula units.

In order to calculate how many formula units a certain mass of a substance contains, you need to do two things

  • determine how many moles are present in that many grams by using the substance's molar mass;
  • determine how many formula units you have in that many moles by using Avogadro's number.

So, use sodium nitrate's molar mass to determine how many moles are present in 2 g

#2cancel("g") * "1 mole "/(85.0cancel("g")) = "0.0253 moles"#

Avogadro's number tells you that 1 mole of any substance contains exactly #6.022 * 10^(23)# molecules of that substance.

This means that you have

#0.02353cancel("moles") * (6.022 * 10^(23)"f. units")/(1cancel("mole")) = color(green)(1.4 * 10^(22)"f. units"#