P- Amount of substance Flashcards
Ar- relative atomic mass
The weighed average mass of an atom of an element, taking into account its naturally occurring isotopes, relative to 1/12 the mass of an atom of carbon-12.
Mr- relative molecular mass
The mass of a molecule of an element or
compound relative to 1/12 the mass of an atom of carbon-12. (sum of all of the Ar in a molecule)
Avogadro’s constant
The number of atoms in 12g of C-12.
/no. of particles in a mole
What does relative formula mass show?
The RATIO of different ions in the compound.
Why would the mass of product made be less than the maximum theoretical mass?
- Reaction did not go to completion (eg. not heated enough)
- Products may have been lost during separation from reaction mixture- left in reaction vessel (eg. filtration)
- Unexpected side products may have been formed
- The reaction may be REVERSIBLE
- Gas formed- escape
Empirical formula
The simplest whole number ratio of the atoms of each element in a compound.
Molecular formula
The actual number of atoms of each element in a compound.
(only applies to substances that exist as molecules)
> may be several UNITS of empirical formula within
What is the assumption made in the ideal gas equation?
Particles don’t interact so there’s
no forces between them.
The ideal gas equation
PV=nRT
P- pressure (Pa)
V- volume (m³)
n- no. of moles
R- molar gas constant (given: 8.31JK⁻¹mol⁻¹)
T- temperature (K)
Unit conversion-
kPa to Pa
x 1000
Unit conversion-
Celcius to Kelvin
+ 273
Unit conversion-
dm³ to m³
/ 1000
Unit conversion-
cm³ to m³
/ 10⁶
Volume of 1 mole of ideal gas at standard temperature (20ᵒC) & pressure (101kPa)
24dm³
What is a solution?
Mixture of solute and solvent particles.
What is the concentration?
Amount of solute in a given amount of solution. (mol dm⁻³)
dm³ & L
mol dm⁻³ = mol/L
mL to dm³
/ 1000
g dm⁻³ to mol dm⁻³
/ Mr
Stoichiometry
Simplest whole no. ratio in which reactants react & products produced in a reaction.
Formula of Suplfate ion
SO₄²⁻
Formula of Carbonate ion
CO₃²⁻
Formula of Nitrate ion
NO₃⁻
Formula of Ammonium ion
NH₄⁺
Formula of Phosphate ion
PO₄³⁻
Give 2 advantages of high atom economy
- Conserves natural resources
- Reduces waste
Formula for % atom economy
Mr of desired product
_________________________ x 100
Mr of all reactants/ all products
(∵ x gain/ loss of atoms)
Accuracy
How close a result is to the TRUE VALUE
Precision
How close results are to EACH OTHER
- for uncertainty ranges
- same amount of decimal places to reading
- x greater/ smaller than +/- half of the smallest division of the instrument (eg. 0.05mL)
Readings (idea)
From SINGLE judgement
eg. reading off a balance, thermometer (x for temp change tho!)
Measurements (idea)
DIFFERENCE between 2 JUDGEMENTS
eg. stopwatch, pipette
# burette- technically has 3 judgement points but the 3rd (endpoint) is subjective ∴ counts as 2
% uncertainty for readings
Error
____________ x 100
Measurement
% uncertainty for measurements
SUM of errors
_____________ x 100
Measurement
eg. SUM for +/- 0.1 –> 0.2
% yield
moles of products/ moles of reactants x100
