CHEM 101 Lecture 2: CHEM 101 Lecture

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10 Oct 2017

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Isotopes: atoms of the same element (same z), but different a: same number of protons, same number of electrons, different number of neutrons. Natural abundance: the percentage of certain isotopes in a natural sample of an element. Percentage of isotopes = 100 x (# of given isotope) / (total # of atoms of that element) Average mass of an element"s atoms = (natural abundance)(mass of isotope n) Avogadro"s idea: put a large number of the same unit on the balance to get a measurable mass, divide this measurable mass by the number of units to get the mass of one individual object, 6. 022 x 10^23. Mole: the conventional macroscale-nanoscale connection: 1 mole = mass (in g) of a substance that equals numerically the atomic mass (in amu) of that substance, counting unit. Molar mass: the mass of one mole (g/mol: same for the same substance, but differs from substance to substance.

Related Questions

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.

There are two stable isotopes of supposium (Su). Su-191=190.9609u(27.30%) Su-194=193.9633 u(72.70%) Compute the atomic mass ofsupposium.
a. 194.0 u b. 193.1 u c. 191.8 u d. 190.9 u e. 192.5 u

Which would not be found with a mass spectrometer.
a. the atomic mass of a single isotope of potassium
b. the number of stable isotopes of potassium c.the mass of aproton
d. the number of protons in potassium e. the relative abundance oftwo isotopes of potassium

How many protons, neutrons, and electrons are in 24 Mg2+?
12
a. 10 protons, 12 electrons, 24 neutrons b. 12 protons, 10electrons, 12 neutrons
c.12 protons, 12 electrons, 24 neutrons d. 24 protons, 10electrons, 12 neutrons
e. 12 protons, 12 electrons, 12 neutrons

1.The age of rocks is sometimes calculated from the measured excessof lead 206 atoms over the normal abundance. The uranium isotopeU-238 decays to lead-206.What is the percent abundance of lead-206if there aare 4.52 X 10^21 atoms of lead-206 in a 198 g sample ofore that is 2.58% lead? a. 27.7 b. 0.0202 c. 4.70 x 10^-3 d. 30.4e. 0.782

2. The average atomic mass of B is 10.80 u. Boron has only twostable froms 10
5 B(10.00 u) and 11
5 B (11.00 u). What is the natural percent abundance of B?
a. 1.0% b. 20% c. 75% d. 3.8% e. 80%

3. 57.7 g Ni contains how many atoms? a. 3.47x10^23 b.0.983 c. 1.24x 10^24
d. 6.13x10^23 e. 5.92x10^23

4. What mass of magnesium is necessary to make 10.5 g of magnesiumbromide if 1.04 g of magnesium makes 7.88 g of magnesiumbromide?
a. 7.89 g b. 1.39 g c. 79.9 g d. 3.66 g e. 1.58 g

5. How many atoms of lead are required to cover a 33.0 cm by 45.0cm area witha sheet of lead that is 0.140 mm thick? The density oflead is 11.35 g/cm3.
a. 1.42x10^26
b. 2.29x10^25
c. 6.86x10^22
d. 2.29x10^26
e. 6.86X10^23

6. The natural abundance of calcium in the earth's crust is 3.4% bymass. How many calcium atoms are present in a 1.50 g sample of theearth's crust?
a. 7.7x10^22 b. 7.7x10^20 c. 3.1x 10^22 d.6.6x10^23 e.5.1x10^20

9.Rubidium possesses two stable forms and has an average mass of85.5. 85Rb has a mass of 84.9 and a percent abundance of 72.2%.What is the mass of the other form of Rb?

a. 85.7 u
b. 88.3 u
c. 86.1 u
d. 89.4 u
e. 87.1 u

10. Which is the more abundant isotope, CI-35 or CI37?
a. CI-17
b. CI-37
c. The two isotopes are equal in balance
d. CI-35
e. A third unstable isotope is more abundant

11. An element has 5 stable isotopes. The mass and percentage ofeach are:
69.9243 20.52%
71.9217 27.43%
72.9234 7.76%
73.9219 36.54%
75.9214 7.76%
The element is which of the following
a. Se b. Ge c. Ga d. As e. Zn

12. Lead-206 has a relative abundance of 23.6%. What sized block oflead (in cubic centimeters) will contain 8.34x10^21 atoms oflead-206? The density of lead is 11.35 is g/cm3.
a. 0.253
b. 0.0107
c. 1.07
d. 12.1
e. 0.330

13. When decomposed chemically, 73.0 grams of a sample of HCIproduce 71.0 g of Cl2 and 2.0 g of H2, while 34.0 g of a sample ofH2s produce 32.0g of S and 2.0g of H2. This is an example of theLaw:
a. of Definate Proportions
b. E=mc^2
c. of multiple proportions
d. of Conservation of Mass
e. none of these

CHEM 101 Lecture 2: CHEM 101 Lecture

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