Formulae, Equations And Amounts Of Substance

Question 1

Define a mole

Answer 1

Unit for amount of substance: the amount of chemical species found in 12g of carbon-12

Question 2

What is Avogadro’s constant?

Answer 2

Number of atoms in exactly 12g of carbon-12.

6.02 x 10^23

Question 3

Define molar mass

Answer 3

Mass of 1 mole of the substance in g/mol

Question 4

Define relative molecular mass

Answer 4

Average mass of a molecule relative to 1/12 mass of carbon-12 atom

Question 5

Define empirical formula

Answer 5

Smallest whole number ratio of atoms of each element in a compound

Question 6

Define molecular formula

Answer 6

Actual number of atoms of each element in a molecule

Question 7

Define spectator ion

Answer 7

Ions that do not take part in the reaction

Question 8

What is a hydrate?

Answer 8

A compound that has waters of crystallisation

Question 9

What is a standard solution?

Answer 9

One with an accurately known concentration

Question 10

What is mass concentration?

Answer 10

Mass of solute per volume unit of solution - gdm^-3

Question 11

What is molar concentration?

Answer 11

Moles of solute per volume of solution - moldm^-3

Question 12

What is a primary standard?

Answer 12

A substance used for preparation of a standard solution

Question 13

What is Avogadro’s law?

Answer 13

Provided the conditions of temperature and pressure are the same, equal volumes of gas contain the same number of molecules

Question 14

What is molar volume?

Answer 14

Volume of 1 mole of gas

Question 15

What is a displacement reaction?

Answer 15

A more reactive element reacts to take the place of a less reactive element in a compound

Question 16

What is a precipitation reaction?

Answer 16

One that produces an insoluble solid (precipitate)

Question 17

What is an error?

Answer 17

A discrepancy between the value obtained in an experiment and the actual value

Question 18

What is precision?

Answer 18

Reference to how close each value is to each other obtained in an experiment

Question 19

What is accuracy?

Answer 19

Reference to how close obtained values are to the actual value

Question 20

What are concordant results?

Answer 20

Results that lie close to each other, usually titrates that lie within 0.20cm^3 (+/- 0.10cm^3)

Question 21

What is a margin of error?

Answer 21

The range in which the true values could lie

Question 22

What are random errors?

Answer 22

They occur when conditions are varied in an unpredictable manner

Question 23

What are systematic errors?

Answer 23

Errors which are constant when you repeat an experiment, usually result of an apparatus used

Question 24

What is the equation for percentage uncertainty?

Answer 24

(Actual yield / theoretical yield) x 100 (%)

Question 25

What is atom economy?

Answer 25

Measure of the proportion of atoms that become part of the desired product in the balanced chemical equation

Question 26

What is the equation for atom economy?

Answer 26

(Mr of desired product / total Mr of all products) x 100 (%)

Question 27

What does each letter of the pv = nRT equation represent?

Answer 27

p = pressure (Pa)
v = volume (m^3)
n = moles (mol)
R = ideal gas constant: 8.314
T = temperature (k)