# Question #ef268

##### 1 Answer

#### Answer:

Here's what I got.

#### Explanation:

I assume that you must determine the number of neutrons present in *one molecule* of sulfuric acid,

The idea here is that you need to use the periodic table to find the mass number of **the atoms** that make up a molecule of sulfuric acid.

As you know, an atom's *mass number* tells you the number of **protons** and **neutrons** said atom contains in its nucleus. Since the number of protons is always given by the element's atomic number, finding the atom's mass number will automatically give you the number of neutrons it has in its nucleus.

So, one molecule of sulfuric acid contains

,twoatoms of hydrogen#2 xx "H"# ,oneatom of sulfur#1 xx "S"# ,fouratoms of oxygen#4 xx "O"#

Now, pull up a periodic table an write the *average atomic weights* of these three elements. You should get

#"For H: " "1.00794 u"#

#"For S: " "32.066 u"#

#"For O: " "15.9994 u"#

As you know, the average atomic weight of an element is determined by taking the *weighted average* of the atomic weighs of its naturally occurring isotopes.

The trick here is to **round these values** to the **nearest integer** - this will give you the mass number of the element's **most abundant isotope**.

In your case, you will have

#"For H: " 1.00794 ~~ 1#

#"For S: " 32.066 ~~ 32#

#"For O: " 15.9994 ~~ 16#

These mass number values will help you *estimate* how many neutrons you get per molecule of sulfuric acid.

Use

#color(blue)("no. of neutrons" = "mass number" - "atomic number")#

to get

#"For H: " 1 - 1 = "0 neutrons"#

#"For S: " 32 - 16 = "16 neutrons"#

#"For O: " 16 - 8 = "8 neutrons"#

One molecule of sulfuric acid will thus have a total of

#overbrace(2 xx 0)^(color(red)("two atoms of H")) + overbrace(1 xx 16)^(color(blue)("one atom of S")) + overbrace(4 xx 8)^(color(purple)("four atoms of O")) = color(green)("48 neutrons")#