# Question ef268

Jan 14, 2016

Here's what I got.

#### Explanation:

I assume that you must determine the number of neutrons present in one molecule of sulfuric acid, ${\text{H"_2"SO}}_{4}$.

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

• two atoms of hydrogen, $2 \times \text{H}$
• one atom of sulfur, $1 \times \text{S}$
• four atoms of oxygen, $4 \times \text{O}$

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

$\text{For H: " "1.00794 u}$

$\text{For S: " "32.066 u}$

$\text{For O: " "15.9994 u}$

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

$\text{For H: } 1.00794 \approx 1$

$\text{For S: } 32.066 \approx 32$

$\text{For O: } 15.9994 \approx 16$

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

Use

$\textcolor{b l u e}{\text{no. of neutrons" = "mass number" - "atomic number}}$

to get

$\text{For H: " 1 - 1 = "0 neutrons}$

$\text{For S: " 32 - 16 = "16 neutrons}$

$\text{For O: " 16 - 8 = "8 neutrons}$

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")#