Moles 1 - Solids

Question 1

Avogadro constant

Answer 1

The Avogadro constant is the number of entities in one mole of a substance

L, (6.02 × 10^23 mol-1)

Question 2

Molar mass

Answer 2

Molar mass of a substance is the mass per mole of the substance (basically atomic mass)
in g mol-1

Multiply the atomic weight of each element with its number of atoms present in the compound

e.g H2O = 2x1 + 1x16 = 18

Question 3

Empirical formula

Answer 3

The simplest whole number ratio of the atoms of each element in the substance

Question 4

Molecular formula

Answer 4

shows the number of atoms of each element in one mole of the substance

Question 5

Relative atomic mass (Ar) definition

Answer 5

The mean mass of an atom of an element, divided by 1/12th of the mean mass of an atom of the carbon-12 isotope

Question 6

Relative molecular mass (Mr)

Answer 6

The mean mass of a molecule of a compound, divided by 1/12th of the mean mass of an atom of the carbon-12 isotope

Question 7

What is term used instead of Mr for iconic compounds?

Answer 7

Relative formula mass

Question 8

How to find the number of particles present in a sample with know mass

Answer 8

Number of particles = amount of substance (mol) * avogradro constant
Number of particles = nL
n = moles
L = avogadro constant (6.022/23 x 10^23)

Question 9

How to find the number of ions present in a sample with know mass

Answer 9

Number of ions = amount of substance (mol) * avogradro constant * number of ions
Number of particles = nL x number of ions
ex - MgCl2 = Mg^2+ & Cl^- = 3 ions
n = moles
L = avogadro constant (6.022/23 x 10^23)

Question 10

How to find the number of atoms present in a sample with know mass

Answer 10

Number of particles = amount of substance (mol) * avogradro constant * atoms
Number of particles = nL x atoms
ex - atoms in N2O4 = 6 (2+4)
n = moles
L = avogadro constant (6.022/23 x 10^23)

Question 11

How to find the number of electrons present in a sample with know mass

Answer 11

Number of particles = amount of substance (mol) * avogradro constant * electrons
Number of particles = nL x electrons

n = moles
L = avogadro constant (6.022/23 x 10^23)

Question 12

How to find amount of substance (moles) in solids

In solids

Answer 12

Number of moles = mass(g)/ Mr or Ar (g/mol)

Question 13

working out concentration in moldm^-3

In solutions

Answer 13

Concentration (moldm^-3) = amount of substance (mol) / volume (dm^3)

Question 14

working out concentration in gdm^-3

In solutions

Answer 14

Concentration (gdm^-3) = mass of substance (g) / volume (dm^3)

Question 15

cm^3 —> dm^3
and
dm^3 —> cm^3

Answer 15

cm^3 / 1000 = dm^3
dm^3 x 1000 = cm^3

Question 16

How to find the empirical formula of a substance

Answer 16

1) write out the elements involved
2) write out the percentages as masses
3) divide these by relative atomic mass to get number of moles
4) divide all numbers by the smallest number of moles to get whole number ratio
5) to find molecular formula, work out Mr of empirical and divide it by Mr of molecular, multiply this by all the atoms in the empirical

Question 17

How to find the empirical formula of hydrocarbon combustion components

Answer 17

1) write out the products (eg H2O and CO2) as headings
2) write the masses of each molecule
3) divide these by the relative molecular mass to get number of moles
4) multiply by the amount of atoms in a molecule (ex for H20 H = 2, so multiply by 2)
5) divide number of atoms (eg C+H) by the smallest number of moles to get the smallest whole number ratio.

Question 18

Ionic equations

Answer 18

Ionic equations show the ions that are formed in solutions and show which particles are reacting

1) split all aqueous components (acids, alkalis, salts)
2) cancel ions that appear on both sides of the equation (spectator ions - they don’t get involved in the recation) to form the simplest ionic equation
3) in the final equation the charges must balance on the left & right of the equation

Question 19

Using chemical equations to work out masses/volumes/concentrations of reactants/products involved in a reaction

Answer 19

1) using info given, find moles
2) find ratio of moles you have to moles of desired thing
3) work out needed thing from moles