4.7, 8.2, 8.3, 8.5 (11-6-19)

A sample of an element with a mass equal to that element's average atomic mass expressed in grams contains ___ mole(s) of atoms.

1

What is a mole? How is it defined?

A mole can be defined as the number equal to the number of carbon atoms in 12.01 grams of carbon. One mole of something consists of 6.022 x 10²³ units of that substance.

We can relate the sample mass to the atomic mass because the ____ are the same.

moles

What is the mass in grams of a 4.86 mol calcium carbonate sample?

100.09 g

What is sodium's atomic number? Will this ever change? What letter do we use to indicate the atomic number?

11; this will never change. Atomic number is indicated using the letter Z.

How many grams of copper contain the same amount of atoms as 16.78 g of aluminum? How do you know this?

63.55; I know this since samples in which the ratio of the masses is the same as the ratio of the masses of the individual atoms always contain the same number of atoms.

What is the molar mass of sulfur dioxide?

64.07 g

What is the mass (in amu) of a sample of carbon that contains 62 amu?

744.62 amu

How is Avogadro's number related to the mole?

Avogadro's number is the number of particles in a mole.

Define formula weight. What is the formula weight of NaCl?

Formula weight is the molar mass for ionic compounds; 58.44 g.

What is an isotope? Give an example?

Isotopes are atoms with the same number of protons but different numbers of neutrons. Examples include sodium-23 and sodium-24.

What is the average atomic mass? What is it for carbon and what does it allow us to do?

Since each isotope has a slightly different mass, we need to use an average mass for an element's atoms. For carbon, it is 12.01 amu. Now that we know the average mass of the carbon atom, we can count carbon atoms by weighing samples of natural carbon.

What is the atomic mass unit? What is its abbreviation? Why is it used?

The atomic mass unit is the term scientists have defined to avoid using complicated numbers. It's abbreviated amu and is used mainly for convenience.

Define molar mass. How is it obtained? What is the molar mass of methane?

The molar mass of any substance is the mass (in grams) of 1 mole of the substance. Th e molar mass of methane is 16.04 g.

What is an atom's mass number? What does it stand for?

The sum of the number of neutrons and the number of protons in a given nucleus is called the atoms' mass number.

How would you figure out how many atoms of hydrogen you have in a bag?

We can do it by weighing the sample.

Why must we count atoms by weighing them?

We can easily count things like jelly beans and mints by weighing. Exactly the same principles can be applied to counting atoms.