Question

Question #0a40a

Answer 1

Here's what I got.

Explanation:

For starters, you know that you're dealing with a thermal decomposition reaction that takes the general form

`"solid " stackrel(color(white)(acolor(red)(Delta)aaa))(->) " solid residue + gas"`

Now, you know that this salt decomposes to give off brown fumes. A well-known gas that matches this description if nitrogen dioxide, `"NO"_2`.

![http://fphoto.photoshelter.com/image/I0000uMvc5g65_yA]()

You can thus say that when the salt undergoes thermal decomposition, nitrogen dioxide is given off.

`"solid " stackrel(color(white)(acolor(red)(Delta)aaa))(->) " solid residue" + "NO"_(2(g))` `uarr`

Now, in order for the reaction to produce nitrogen dioxide, the white salt must contain the nitrate anion, `"NO"_3^(-)`. Furthermore, you can say that the solid residue will be an oxide.

So all you have to do now is look for an element that has

• a white salt when combined with the nitrate anion
• a yellow oxide

A suitable candidate here is lead, `"Pb"`. Lead(II) nitrate is indeed a white salt

![https://en.wikipedia.org/wiki/Lead(II)_nitrate]()

and lead(II) oxide is a yellow salt

![https://en.wikipedia.org/wiki/Lead(II)_oxide]()

which means that you're dealing with the thermal decomposition of lead(II) nitrate, which produces lead(II) oxide, a yellow solid residue, and brown fumes of nitrogen dioxide. Also, keep in mind that in addition to the nitrogen dioxide, this reaction also produces oxygen gas, `"O"_2`,

The balanced chemical equation that describes the reaction looks like this

`2"Pb"("NO"_ 3)_ (2(s)) stackrel(color(white)(acolor(red)(Delta)aaa))(->) 2"PbO"_ ((s)) + 4"NO"_ (2(g))` `uarr + "O"_ (2(g))uarr`