Topic 5 : Calculations

Question 1

Accuracy

Answer 1

How close an individual result is to the accepted value (closer=more accurate)

Question 2

Error

Answer 2

Difference between individual measurements and the accepted reference value

Question 3

Precision

Answer 3

accuracy under the same conditions, depends on distribution of random errors and doesn’t relate to the true value of

Question 4

Uncertainty

Answer 4

Estimate attached to range of measurements within which true value lies
( ex. 55 +- 0.5 = 54.5<x<55.5)

Question 5

Reliability

Answer 5

Opposite of uncertainty

Question 6

Avogadro’s Constant

Answer 6

Number of atoms in one mole of a substance = 6.022x10^23
Number of ions = mol x constant

Question 7

Molar mass (Mr)

Answer 7

Mass of one mol of substance
Mass = Mr x mol

Question 8

Percentage yield

Answer 8

actual yield (amount) / theoretical yield
If the actual is less than the theoretical, it is the limiting reactant
Reasons why they are not equal:
1) reversible reactions don’t go to completion
2) some product lost when separated from reaction
3) some reactants react in an unexpected way

Question 9

Atom economy

Answer 9

Mass of atoms in desired product / mass of atoms in reactant
Higher atom econ = less wasteful reactant

Question 10

Combustion analysis

Answer 10

Products are always H2O and CO2

Question 11

Neutralisation reactions

Answer 11

Acid + base -> salt + water
ionic equation needs to be simplified to net

Question 12

Ideal Gas Equation

Answer 12

PV = nRT
R=Gas Constant 8.31Jmol-1k-1
T(K) = T(ºC) + 273
Pressure in Pa
Volume in m3