Stoichiometry

Question 1

How many atoms in a mole of any given element?

Answer 1

6.02 * 10^23 atoms

Question 2

In simplified terms, what is a mole?

Answer 2

A unit to measure the amount of atoms in a sample. It’s defined as the amount of a substance when it contains exactly 6.02*10^23 atoms of that substance.

Question 3

How do you find moles of a substance?

Answer 3

For an element, look at the amu of that element. Not only does that number tell you the amu of that element, it also tells you how many grams it takes to get exactly 6.0210^23 atoms. That’s the unit for moles.
For example, a single atom of Lithium weighs 6.94 amu. Also, it takes 6.94 GRAMS of Lithium to have 6.0210^23 atoms. So, we get a conversion factor: 6.94g/mole, which we can then use to convert to and from moles.

Question 4

When determining the mass (molar or amu) of a molecule, which rule for significant figures should you use: addition, subtraction, multiplication, or division?

Answer 4

Addition, because the chemical formula must be exact.

Question 5

Define Hygroscopic.

Answer 5

Readily absorbing moisture, even from the atmosphere.

Question 6

What is an anhydrous compound?

Answer 6

Compound that was hydrated but has had all water removed from it

Question 7

Chemical formulas are in terms of _____.

Answer 7

Moles (an exact amount of atoms!)

note: this is important because you can relate the number of moles of each molecule/atom to the moles of other molecules/atoms in the formula.

Ex:

N2 + 3H2&raquo_space;> 2NH3

We can say that for every amount (in moles) of N2, there’s a product of 2 times that amount (in moles) of 2NH3.

Question 8

True or false: The conversion relationships you get from a chemical equation are exact.

Answer 8

True.

Question 9

Define Limiting Reactant.

Answer 9

The reactant in a chemical formula that runs out first, thereby limiting the amount of product(s) that can be made.