Isotopes and Atomic Mas Lab

Lab: Isotopes and Atomic Mass

Introduction:

Isotopes are atoms of the same element that have different masses because they contain different numbers of neutrons.  The atomic mass of an element is the weighted average of the masses of the isotopes of that element.  The weighted average takes into account both the mass and the percent abundance of each isotope as it occurs in nature.  The percent abundances and masses of small atomic particles are measured in the laboratory by an instrument called a mass spectrometer.  The mass spectrometer separates particles by mass and measures the mass and percent abundance of each.  From these data a weighted average is calculated to determine the atomic mass of the element.

In this lab you will carry out experiments and perform the necessary calculations to determine the atomic mass of the fictitious element “vegium.”  The element “vegium” has three isotopes called beanium, peaium, and cornium.  As you would expect, each vegium isotope has a different mass.  From a sample of vegium atoms you will determine the relative abundance of each isotope and the mass of each vegium isotope.  From this data you will calculate the weighted average mass, or atomic mass, of vegium.  (Please note: Unlike real isotopes, the individual isotopic particles of vegium differ slightly in mass.)

Purpose:          

• To determine the atomic mass of each isotope of the fictitious element “vegium.”
• To determine the percent abundance of each of the three isotopes of vegium.
• To calculate from experimental data the average atomic mass of vegium.

Materials:     

• Balance
• Sample of vegium (plastic cup with assorted corn, bean, and pea seeds)
• Calculator