CHEM 1A Chapter Notes - Chapter 3: Limiting Reagent, Reagent, Molar Mass

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browncod58

3 Oct 2016

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UCSB

Department

Chemistry and Biochemistry

Course

CHEM 1A

Professor

Joseph

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CHEM 1A Full Course Notes

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Chemical stoichiometry is the quantities of materials consumed and produced in chemical reactions. Ex: 12c is assigned a mass of exactly 12 atomic mass units (amu), and the masses of all other atoms are given relative to this standard. Atoms or molecules are passed into a beam of high-speed electrons. The most accurate method currently available for comparing the masses of atoms. The atomic number on the periodic table is the average of all the isotopes on earth for that element. For example, carbon-12 has a mass of 12. 01 because of the isotopes carbon-13 and carbon-14. Even though natural carbon does not contain a single atom with mass 12. 01, for stoichiometric purposes we consider carbon to be composed of only one type of atom with a mass of 12. 01. Also used to determine the isotopic composition of a natural. The number equal to the number of carbon atoms in exactly 12 grams of pure 12c.

Related Questions

Current convention defines 1 amu as exactly 1/12 the mass of anatom of the isotope 12C. Since most elements occur naturally inwell-established fixed relative abundances of different isotopes,the so-called Atomic Mass for a particular element represents aweighted average of the masses of the individual isotopes. Forexample, naturally occuring carbon is a mixture of 98.90% 12C(12.000000 amu) and 1.10% 13C (13.003355 amu) plus a trace of 14C(14.003241 amu). The Atomic Mass of carbon is found to be 12.011amu.
A Molecular Mass is the sum of the (averaged) Atomic Masses for allatoms in a molecule.

What is the Molecular Mass of H2SeO3?

I am doing the Atomic Mass of Metallo

You may have noticed on the periodic table that the atomic mass of an element is usually not a whole number. That happens because of isotopes. An atom that is missing a neutron or has an extra neutron is called an isotope. They are still the same element; however, they are just a little different from every other atom of the same element.

Most of the carbon atoms in the universe are Carbon-12, with 6 neutrons. A small percentage of carbon atoms are Carbon-13, with 7 neutrons, and an even smaller percentage are Carbon-14 and have 8 neutrons. Carbon-13 and Carbon-14 are isotopes of carbon.

Atomic mass is calculated by determining how many atoms of each isotope type are present in the universe. Since the isotopes of carbon make up only a small percentage of the carbon in the universe, the average of the masses of all carbon atoms is slightly higher than 12, so the atomic mass for carbon is actually 12.011.

Objective

Analyze the isotopes of âMetalloâ and to calculate its atomic mass

Materials

sample of metallo (bag of mixed nuts, bolts, and washers)

balance

Procedures

Obtain a sample of the new element âMetallo.â

Separate the three isotopes of Metallo (nuts, washers, bolts) and measure the mass of each isotope.

Count the numbers of each isotope.

Record all data in the table.

Data Table

	Nuts	Bolts	Washers	Totals
Total Mass (g)
Number

Average Mass (g)
Percent Abundance
Relative Abundance
Relative Mass

Analysis

Calculate the average mass of each isotope by dividing the total mass by the number of particles of that isotope. Record your answers on the Data Table.

Calculate the percent abundance of each isotope by dividing its number of particles by the total number of particles and multiplying by 100. Record your answers on the Data Table.

Calculate the relative abundance of each isotope by dividing the percent abundance from Step 2 by 100. Record your answers on the Data Table.

Calculate the relative mass of each isotope by multiplying its relative abundance from Step 3 by its average mass. Record your answers on the Data Table.

Calculate the average mass of all Metallo particles by adding the relative masses. This average mass is the atomic mass of Metallo.

Explain the difference between percent abundance and relative abundance. What is the result when you total the individual percent abundances? The individual relative abundances?

The percent abundance of each isotope tells you how many of each kind of isotope exist in every 100 particles. What does relative abundance tell you?

Compare the total values for Rows 3 and 6 in the Data Table. Explain why the totals differ and why the value in Row 6 best represents the atomic mass.

CHEM 1A Chapter Notes - Chapter 3: Limiting Reagent, Reagent, Molar Mass

CHEM 1A Full Course Notes

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