S1.4 - counting mass by particles: the mole

Question 1

What is Avogadro’s constant?

Answer 1

One mole contains 6.03 x 12^23 elementary entities with SI unit of the mol

Question 2

What is an elementary entity?

Answer 2

An atom, molecule, ion, electron or any other particle or group of specified particles

Question 3

What is Ar?

Answer 3

Relative atomic mass - molar mass of a substance measured in g mol-1.

Question 4

What is Mr?

Answer 4

Relative formula mass - sum of weighted average atoms of an element in a formula unit relative to 1/12 of an atom of carbon-12.

Question 5

What is the equations involving moles, mass and Mr?

Answer 5

moles = mass / Mr

Question 6

How do you convert between moles and particles?

Answer 6

moles –> particles = x Avogadro’s constant
particles –> moles = / Avogadro’s constant

Question 7

What is the empirical formula?

Answer 7

Empirical formula - simplest whole number ratio of the elements in a compound.

Question 8

What is the molecular formula?

Answer 8

Molecular formula - actual number of atoms of each element present in a molecule.

Question 9

How do you work out RAM?

Answer 9

RAM = % abundance x atomic mass of isotope

Question 10

How can you convert % by mass to empirical formula?

Answer 10

1) Convert each element to moles by dividing mass by Mr
2) Divide the moles by the smallest number
3) Approximate to the nearest whole number

Question 11

How do you convert empirical formula to % by mass?

Answer 11

1) Calculate the Mr of each element.
2) Total the mass of the atoms.
3) Divide by M and multiply by 100.

Question 12

How can you work out empirical formula of MgO?

Answer 12

1) Calculate moles of Mg used.
2) Calculate moles of O that reacted from the increase in mass.
3) Express ratio of Mg:O in the simplest form.
4) Ratio of moles is equal to ratio of atoms.

Question 13

What is a hydrated salt?

Answer 13

Compounds that contain a fixed ratio of water molecules known as water of crystallization within the crystalline structure of the compound.

Question 14

What is molar concentration?

Answer 14

Concentration (g/dm3) = mass / volume

Question 15

What is the solution?

Answer 15

Solution - mixture of the solute dissolved in the solvent.

Question 16

What is the solvent?

Answer 16

Solvent - liquid in which the solute dissolves in.

Question 17

What is the solute?

Answer 17

Solute - solid in which the solvent dissolves in.

Question 18

What is a standard solution?

Answer 18

Standard solution - chemicals prepared to a known concentration and transferred to a volumetric flask.

Question 19

What is serial dilution?

Answer 19

Serial dilution - slowly reducing concentration by a fixed amount each step.

Question 20

What does a calibration curve show?

Answer 20

Calibration curve - using the absorbance to find the concentration

Question 20

What is UV spectroscopy used for?

Answer 20

UV spectroscopy - quantitative technique used to measure absorbance of a substance.

Question 21

What is the equation linking moles, concentration and volume?

Answer 21

concentration = moles x volume

Question 22

How can you work out molar concentration?

Answer 22

molar concentration (gdm3) = mass / volume

Question 23

What is Avogadro’s Law?

Answer 23

Avogadro’s law - moles is directly proportional to volume.