Chapter 1 ~Moles And Equations

Question 1

Definition of relative atomic mass (Ar)

Answer 1

The relative atomic mass is the weighted average mass of naturally occurring atoms of an element on a scale where an atom of carbon - 12 has a mass of exactly 12 units.

Question 2

Formula for relative atomic mass of element Y:

      Ar [element Y] =

Answer 2

=average mass of one atom of element Y x 12

÷by

Mass of one atom of carbon - 12

Question 3

Definition of nucleon number

Answer 3

°The total number of neutrons and protons in the nucleus of an atom ⚛

(extra information :the number is written either on top of the element or next to the element e.g. C-14)

Question 4

Definition of relative isotopic mass

Answer 4

°the mass of a particular isotope of an element on a scale in which an atom of the carbon-12 isotope has a mass of exactly 12 units

Question 5

Definition of relative formula mass

Answer 5

°the mass of one formula unit of a compound measured on a scale on which an atom of carbon-12 isotope has a mass of exactly 12 units

Question 6

Definition of relative molecular mass

Answer 6

°the mass of a molecule measure on a scale in which an atom of the carbon-12 isotope has a mass of exactly 12 units

Question 7

The 3 steps of determining the Ar (relative atomic mass) from a mass spectra :

Answer 7

1. Multiple each isotopic mass by its percentage abundance
2. add all the figures together
3. Divide by 100

Question 8

The definition for a mole of a substance :

Answer 8

° one mole of a substance is the amount of that substance that has the same number of specific particles (atoms, molecules or ions) as there are atoms in exactly 12g of the carbon-12 isotope

Question 9

Definition of molar mass

Answer 9

°the mass of one mole of a substance in grams

Question 10

Definition of Avogadro constant :

Answer 10

°the number of atoms (or ions or molecules or electrons) in a mole of atoms (or ions or molecules or electrons) :it’s numerical value is 6.02 x 10^23 (Ten to the power of 23)

Question 11

Formula of the number of moles (Mol) =

Answer 11

=Mass of substance (g)÷/

÷molar mass(g.mol^-1)

Question 12

Formula of mass of a substance in grams =

Answer 12

= n (num moles) x M(molar mass)

Question 13

Definition of stoichiometry

Answer 13

The mole ratio of the reactants and products in the balanced equation for a reaction

Question 14

In order to find the mass of products formed in a chemical reaction we use 3 things,
Namely?

Answer 14

1. The mass of the reactants
2. The molar mass of the reactants
3. The balanced equation

Question 15

Formula for the stoichiometric numbers

Answer 15

=masses in the reactions ÷ by Ar values

Question 16

Percentage composition by mass =

Answer 16

~(Ar x number of moles of a particular element in a compound)

~÷

~(molar mass of compound)

~x 100

Example : Fe2O3 calculate irons mass %
(Ar values : Fe=55.8, O=16)

(55.8 x 2) / (55.8x2)+(16x3)

Ans x 100

Question 17

Definition of empirical formula

Answer 17

°simplest whole number ratio

Question 18

Definition of molecular formula :

Answer 18

°The formula that tells you the actual numbers of each type of atom ⚛ in a molecule

Question 19

The formula for an ionic compound is always its…..

Answer 19

Empirical formula

Question 20

The empirical formula can be deduced in 2 methods :

Answer 20

1. determining the mass of each element present in a sample of the compound
2. From data that gives the percentage composition by mass of the elements in a compound

Question 21

What 2 things do we need to deduce the molecular formula?

Answer 21

1. the relative formula mass of the compound

2. The empirical formula

Question 22

3 Steps of determining the molecule formula :

Answer 22

1. Find the empirical formula mass
2. Divide the relative molecular mass by the empirical formula mass to get the determining factor

3.multiply the number of atoms in the empirical formula by the determining factor.
Then you have the molecular formula

Question 23

Definition of state symbols

Answer 23

°a symbol used in a chemical equation that describes the state of each reactant and product

s-solid
l-liquid
g-gas
aq- aqueous solution

Question 24

Definition of spectator ions :

Answer 24

°ions present in a reaction mixture that do not take part in the reaction (are on both sides of the ionic equation)

Question 25

The 4 steps of writing an ionic equation are....

Answer 25

1. Write down the full balance equation 2. Write down all the ions present. NB!!! Any reactant /product with state symbols : (s), (l), (g) or is a molecule in solution e.g. Cl2 in MgCl2 forms (Mg ^2+ and 2Cl^-) so the chlorine is together. Does NOT split into ions 3. cancel spectator ions 4. write down equation omitting the spectator ions

Question 26

What is a precipitation reaction?

Answer 26

A reaction where 2 aqueous solutions react to form a solid-the precipitate

Question 27

2 steps in writing the ionic equation for a precipitate reaction :

Answer 27

1. Write formula of the precipitate as the product | 2. Write the ions that go to make up the precipitate as the reactants

Question 28

How to change cm^3 to dm^3?

Answer 28

By dividing the number of cm^3 by 1000

Question 29

Formula for concentration (mol dm^3) =

Answer 29

=number of moles(mol) ÷volume(dm^3) =n/V

Question 30

Number of moles(mol) =

Answer 30

C x V

Question 31

Definition of titre:

Answer 31

°in a titration, the final burette reading minus the initial burette reading

Question 32

The 3 steps of calculating the solution concentration by titration :

Answer 32

1. Calculate the moles of acid using the formula n=m/M 2. Us the stoichiometry of the balanced equation to calculate the moles of base 3. Then calculate the concentration of base using the formula c=n/v *can be visa versa

Question 33

3 Steps of deducing the stoichiometry by titration :

Answer 33

1. Calculate the number of moles of each reagent using the formula n = C x V (remember in dm^3) NB!!! if in cm^3 than ÷by 1000 2. Deduce the simplest mole ratio 3. write the equation

Question 34

What is a titration?

Answer 34

A (laboratory) method or technique of determining the unknown concentration of a solution by reacting it with a known concentration of a substance. (an acid and base)

Question 35

What is the molar gas volume?

Answer 35

24dm^3

Question 36

Formula for number of moles of a gas, n (mol) =

Answer 36

= V(dm^3) ÷ 24dm^3

Question 37

Volume of a gas (dm^3) =

Answer 37

Number of moles, n (mol) x 24dm^3

Question 38

What is a molar (M)?

Answer 38

A measure of concentration, equilavent to mol.dm^-3