How do scientists determine the number of neutrons in an isotope of an atom?
o
they add the number of protons and electrons.
o
they subtract the number of protons and neutrons from the mass number
o
they subtract the number of protons from the mass number
o
they subtract the number of electrons from the mass number

Option (c) is the correct answer.

Explanation:

Isotopes are the species that contain same number of protons but different number of neutrons.

For example, isotopes of carbon are and .

So, both these atoms contain six protons but different number of neutrons.

As sum of total number of protons and neutrons present within an element is known as atomic mass.

Hence, number of neutrons can be calculated as follows.

                      Atomic mass = atomic number + no. of neutrons

                  No. of neutrons = atomic mass - atomic number

Thus, we can conclude that scientists determine the number of neutrons in an isotope of an atom as they subtract the number of protons from the mass number.

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol