3. Stoichiometry

Question 1

What is stoichiometry?

Answer 1

The study of the quantitative relationships in substances and their reactions

Question 2

what is 1 mole?

Answer 2

the unit chemists use when counting numbers of atoms or molecules in a sample

6.022x10^23 of something

Question 3

what is Avogadro’s number?

Answer 3

6.022x10^23 particles= 1 mole

Question 4

Which element does mole have a connection to?

Answer 4

12g of Carbon12 has 6.022x10^23 atoms.

Question 5

What is an elements mass of 1 mole?

Answer 5

It’s the amu written for each element on the periodic table.

Question 6

how do you convert from moles of substance to number of atoms/molecules?

Answer 6

(moles of substance/1) * (Avogadro’s number/1 mole)

Question 7

how do you convert from mass of an atom to moles?

Answer 7

(grams/1) * (1 mole/grams molar mass)

Question 8

How do you convert from moles to mass?

Answer 8

moles * (grams/1 mol)

Question 9

how many nitrogen atoms are in 30g of nitrogen?

Answer 9

(30.g/1) * (1 mol N/14.0067gN) * (6.022*10^23 atoms/1 mole N) = 1.3 *10^24 N atoms

Question 10

what is the abbreviation of mole?

Answer 10

mol

Question 11

what is molar mass?

Answer 11

The mass (g) of 1 mole of substance.
It is related to the atomic weight of an element.

Question 12

how many significant figures are generally used to report molar mass of an element or compound?

Answer 12

to two decimal places

Question 13

What is the percent composition of an element in a compound?

Answer 13

“the mass of an element present in exactly 100g of a compound”

Question 14

What is the equation for calculating percent composition of an element in a compound?

Answer 14

example
%H in H2O= [2 mol H(1.01g/1 mol H)]/[1mol H2O(18.02g/1 mol H2O)]
*100%=11.2%H

Question 15

What equation can you use to determine a molecular formula from an empirical formula?

Answer 15

molar mass of compound/
molar mass of empirical formula

Question 16

what is an empirical formula?

Answer 16

the simplest whole number ratio
of the elements in the formula

Question 17

How would would you go about calculating %H in H2O?

Answer 17

1. calculate mass of H2O
2. mass of H/mass of H2O*100%

Question 18

How do you determine formula of hydrated salts? You are given grams before and after heating.

Answer 18

1. the mass after heating is the mass of salt
2. the before mass-after mass=mass of the water
3. convert the after mass from g to moles (need mol mas off salt)
4. convert water mass to moles (need mol mass of water)
5. water mol/

Question 19

What is a hydrated ionic compound?

Answer 19

an ionic compound that has a well-defined amount of water trapped within the crystalline solid