# Question 7504a

Dec 10, 2015

Here's what I got.

#### Explanation:

You're actually dealing with a coordination compound called hexamminechromium(III) nitrate, which consists of the hexaamminechromium(III) complex ion, "Cr"("NH"_3)_6^(3+), and the nitrate anion, ${\text{NO}}_{3}^{-}$.

More specifically, the coordination compound consists of one hexamminechromium(III) complex ion and three nitrate anions.

So, how many elements are a part of this compound? To figure that out, break up the complex ion and the nitrate anion into their respective constituent elements.

Notice that $6$ subscript that follows the ammonia ligands. This means that the complex ion contains six ammonia molecules, ${\text{NH}}_{3}$, so make sure that you keep track of all these atoms.

You can thus say that "Cr"("NH"_3)_6^(3+)# contains

• one chromium atom, $\text{Cr}$
• six nitrogen atoms, $\text{N}$
• eighteen hydrogen atoms, $\text{H}$

Now focus on the nitrate anion. Notice that it has a $3$ subscript, so keep that in mind when listing the number of atoms it contains.

You can say that three nitrate anions, $3 \times {\text{NO}}_{3}^{-}$, will contain

• three nitrogen atoms, $\text{N}$
• nine oxygen atoms, $\text{O}$

So, this coordination compound contains four distinct elements

• chromium
• hydrogen
• nitrogen
• oxygen

Add up all the atoms we've listed above to get the total number of atoms per element

• chromium: $1 \to$ from the complex ion
• hydrogen: $18 \to$ all from the complex ion
• nitrogen: $9 \to$ $6$ from the complex ion and $3$ from the three nitrate anions
• oxygen: $9 \to$ all from the nitrate anions

The total number of atoms present in the compound will be

$\text{no. of atoms} = 1 + 18 + 9 + 9 = 37$