Stoichiometry

Question 1

602 000 000 000 000 000 000 000 is equal to what 4 concepts????

Answer 1

equal to 1 mole; Avogadro’s number; equal to formula mass of a compound or element; equal to volume of 1 mole of gas at STP.

Question 2

How do you determine formula mass?

Answer 2

Look up atomic masses of elements in the compound and multiply number of each element by atomic mass and then add up all the subsets.

Question 3

How does formula mass relate to the mole?

Answer 3

The formula mass is equivalent to 1 mole

Question 4

What is the equation for finding a mole amount if you know the given mass?

Answer 4

Mole = Given Mass / Formula Mass

Question 5

How do you convert a given molecule amount into moles?

Answer 5

Divide the given molecule amount by Avogadro’s number.

Question 6

Can you go directly from mass of a sample to molecules?

Answer 6

No! You have to convert mass to moles (by dividing by the formula mass) and then multiply by Avogadro’s Number.

Question 7

How do you convert moles of a gas at STP into volume?

Answer 7

Multiply the moles of gas by 22.4 L/ mole.

Question 8

How do you convert Liters of gas at STP into moles?

Answer 8

Divide the Liters of gas by 22.4 L/ mole.

Question 9

Can you convert Liters of gas at STP directly into molecules?

Answer 9

No, you have to convert Liters to moles (divide by 22.4 L/ mole) and then multiply by Avogadro’s Number.

Question 10

How can you relate volume of gas (at STP) to formula mass.

Answer 10

Since 1 mole = 22.4 L of gas at STP and
1 mole = Formula Mass
Formula Mass/ 22.4L are equivalent concepts and could be used to set up ratios. This also relates to Density since the Mass/Volume is in proportion to the same units.

Question 11

What do the coefficients in a balanced chemical equation represent?

Answer 11

The coefficients represent the mole ratios of the reactants and products. They also can represent volume amounts of gases at STP.

Question 12

How can you use the coefficients in a balanced chemical equation to solve problems?

Answer 12

You use the given amount/ related coefficient and set it equal to the unknown amount/ related coefficient.

Question 13

Why is the mole the “Heart of Chemistry”?

Answer 13

You have to go through the mole in order to convert mass to molecules or volume to molecules or mass to volume or any variation of those conversions!

Question 14

What is the formula mass of water?

Answer 14

H2O : 2Hydrogen x 1 amu = 2 amu 1 Oxygen x 16 amu =16 amu ; 2 +16 = 18 amu or 18 g/mole

Question 15

What is the volume of 25 grams of water

Answer 15

D= M/V so 1 g/ml = 25g/V ; V= 25g/ 1 g/ml = 25 ml

Question 16

if you have 36 grams of water, how many moles do you have?

Answer 16

36 g/18 g/mole = 2 moles

Question 17

3.01 x 10 23 molecules is how many moles?

Answer 17

3.01 x 10 23molec/ 6.012 x 1023 molec/mole = 0.5mole

Question 18

How many molecules are in 44.8 L of Ne at STP?

Answer 18

44.8L/22.4 L/mole = 2 moles

2 moles x Avogadro’s Number = 1.2 x 10 24 molecules

Question 19

How much does 44.8 L of Ne at STP weigh?

Answer 19

44.8L/22.4 L/mole = 2 moles

2moles x 20 g/mole = 40 grams

Question 20

How many atoms of Helium are present in 11.2 L of Helium at STP?

Answer 20

11. 2L/ 22.4 L/mole = 0.5 mole

0. 5 mole x Avogadro’s Number = 3.01 x 10 23 molecules