How can you calculate the number of neutrons in an atom?

Number of neutron can be simply calculated by:

Number of neutron=mass number-atomic number

As;

Mass number is the sum of number of proton and neutron in an atom

And

Atomic number is the number of proton in an atom.

If we don't know the mass or atomic number of an atom.we can got it from periodic table in which mass number is given on top and atomic number in bottom.

For example

In sodium; the mass number is 23

Atomic number is 11

By applying formula

No.of neutron=23-11=12

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol