Chapter 3 Amount Of Substance

Question 1

What is the Avogadro constant And what does it mean?

Answer 1

6.02x10^23 and if you multiply the number of moles by this you will find the amount of atoms in a sample

Question 2

What is the calculation for miles with mass and Mr?

Answer 2

n=m/Mr

Question 3

How can you find the empirical formula of a product from the mass of its reactants?

Answer 3

1. Convert the masses into moles
2. Find the smallest whole number ratio (divide by the smallest amount of moles)
3. Write the formula from the whole number ratio

Question 4

What is a hydrated salt?

Answer 4

This means that water molecules have formed a part of the crystalline structure, often creating coloured crystals.
If the substance is heated the bonds holding the water to the salt are broken forcing water to leave the compound and evaporate.
This creates an anhydrous Version of the salt
Aka
CuSO4.5H2O -> CuSO4 + 5H2O

Question 5

How do you calculate the water of crystallisation in a hydrous salt compound?

Answer 5

1. Calculate the moles of anhydrous salt
2. calculate the mass and moles of water
3. Find the smallest whole number ratio
4. Write the value for x in the compound

Question 6

What can decrease the accuracy of your experiment formula?

Answer 6

Assumption 1. All water has been lost/ there are no contaminants in the reactants
Assumption 2. There has been no further decomposition or side factions
Assumption 3. No reactants are stuck in apparatus

Question 7

What is the equation for moles and solution volumes?

Answer 7

n= c x V

Question 8

What is a standard solution?

Answer 8

A solution of known concentration

Question 9

What other type of concentration is there?

Answer 9

Mass concentration g/dm^3

Question 10

What constant between moles and gas volumes can be used to create an equation?

Answer 10

At the same temperature and pressure, equal volumes of different gases contain the same number of molecules.

At RTP 1 mol of Gad occupies 24dm^3 approx.
n=V/24 for dm3
n=V/24000 for cm3

Question 11

What is the ideal gas equation?

Answer 11

pV = nRT
p= pressure Pa RTP-> 101,000Pa
V= volume m3
n= moles
R= ideal gas constant 8.31 J/mol/K
T= temperature K RTP-> 298K

Question 12

What is stoichiometry?

Why is it used?

Answer 12

It is the balancing of numbers to give the ratio of moles in a reaction equation
It is used to find the quantities of reactants required to prepare a required quantity of product without waste

Question 13

What is percentage yield, and why might it not be 100%?

Answer 13

The maximum possible amount of product is the theoretical yield but this is difficult to achieve because:
The reaction may not have gone to completion
Other side reaction may have taken place
Purification of the product may result in some loss
The actual yield is usually lower
% yield= actual/ theoretical x100

Question 14

How can the % yield be calculated step by step?

Answer 14

1. Calculate the mol of a reactant
2. Use stoichiometry to calculate the theoretical yield of the desired product in mol
3. Calculate the actual yield of the desired product in mol
4. Use the equation to find a %

Question 15

What is the limiting reagent?

Answer 15

You have two reactants in your reaction with one in excess. The one that is not in excess will be completely used up first and stop the reaction. This is the limiting Reagent

Question 16

What is atom economy?

Answer 16

A measure of how well the atoms have been utilised

It is based solely on the balanced chemical equation for a reaction and assumes 100% yield

Question 17

What are the characteristics of reactions with high atom economies?

Answer 17

Produce a large proportion of desired products and few unwanted waste products
Are important for sustainability as they make the best use of natural resources

Question 18

What is the equation for atom economy?

Answer 18

Atom economy = (sum of molar mass of desired products/ sum of molar mass of all products) x 100