1.2 Amount Of Substance Flashcards
What type of elements are monatomic
Noble gases (all) are monatomic
He is helium
Ne is neon
Etc
Which elements are always found diatomic
H2
N2
O2
All halogens (eg. Cl2)
What are the formulas for phosphorus and sulfur
P4
S8
What are the formulas for metallic elements
They are monatomic (eg. Fe)
What are the formulas for the four giant covalent structures
C (diamond, graphite, graphene)
Si (silicon)
What’s the formula for methane
CH4
What’s the formula for hydrogen sulfide
H2S
What’s the formula for sulfuric acid
H2SO4
What’s the formula for phosphoric acid
H3PO4
What’s the formula for giant cov silicon dioxide
SiO2
What’s the formula for silver, zinc, hydrogen carbonate, hydride, and phosphate (5)
Silver (Ag +)
Zinc (Zn 2+)
Hydrogen Carbonate (HCO3 -)
Hydride (H-)
Phosphate (PO4 3-)
What does substance + oxygen make?
substance + oxygen = oxides
- Metal + oxygen = metal oxide
- Hydrogen Sulfide + Oxygen = Sulfur Dioxide + Water (H2S + 3 O2 = 2 H2O + 2 SO2)
- Hydrocarbon + Oxygen = Carbon Dioxide + Water (C3H8 + 5 O2 = 3 CO2 + 4 H2O)
Any Carbon or Sulfur in the reactants ALWAYS turns into a dioxide in products
What does metal + water make
mwah
metal + water = alkali (always OH) + hydrogen
2 Na + 2 H2O = 2 NaOH + H2
What does metal + acid make
mash
metal + acid = salt + hydrogen
What does oxide/hydroxide/carbonate + acid make
baws
oxide/hydroxide + acid = salt + water
carbonate + acid = salt + water + carbon dioxide
What’s the equation for hydrogencarbonate + acid
hydrogencarbonate + acid = salt + water + carbon dioxide
What’s the equation for ammonia + acid
ammonia + acid = ammonium salt
NH3 + HCl —> NH4Cl
What’s the equation for metal carbonate + heat
metal carbonate = metal oxide + carbon dioxide
How to work out limiting reagents
We need to work out wch reactant is in excess and wch is limiting
For example…
..
2SO2 + O2 —>2SO3
We have 5 mol of SO2, and 2 mol of O2
With 5SO2, we need 2.5O2
With 2O2, we need 4SO2
This means O2 is the limiting reagent as is causes less product to be reduced
What’s average bond enthalpy
With the energy needed to break one mole of a specific bond
In a molecule in gaseous state
Usually, reactants are endothermic (take in energy to stay separated) (+number)
Products are exothermic (let out energy to stay together) (-number)
—> they energy required to break a specific bond
- has same value as energy released when that bonds formed
How to find molecular formula from Mr of empirical formula
Empirical = CH2
Mr (for molecular formula) = 42
- Find formula mass of empirical..
14
Mr / empirical Mr = 42/14 = 3
Molecular formula = 3 x Empirical = C3H6
How to find empirical formula of compound
From its composition (percentage or mass)
Write the mass/percentage of each element
Divide each mass/percentage by Ar of element
NOT Mr
Find simplest whole number ratio of these numbers
Divide by the smallest number
Then multiply to make whole numbers
What’s the ideal gas law 🟡
To do equations with gases, we treat all gases like ideal gases
(No forces between particles, particle size is insignificant etc)
Ideal gas law is used for all gases..
PV = nRT
pressure, vol (m3), number moles, gas constant, temp (k)
- R= 8.31 J mol-1 K-1
- K = °C + 273
What does a volume of gas depend on
Depends on temperature, pressure and number of moles
What the gas is doesn’t affect the volume
Means under same conditions (temp and pressure)
Eg. 100cm3 of one gas contains same number of moles as 100cm3 of any other gas
Room temperature and pressure
25°C and 101kPa
Dilution calculation
N = CV
Moles = conc x volume (dm3)
How to do titration calca (and base)
Yaaa
How do you prepare a burette for use? Apparatus needed?
- burette
- pipette with safety filler
- volumetric flask
- conical flasks
To prepare..
Rinse burette with deionised water
Ensure water flows through jet, then discard water
Rinse burette with solution you’re filling with
Discard it once know it flows through
Discard solution
Charge burette with solution you’re filling with
🚨In titrations what effect will rinsing burette with dionised water have on titre value
- titre value increases
- as solution would be more dilute, with a larger volume
Why should you use the sample youre filling the burette with to rinse instead of water
- water would dilute the sample
- use of water will change conc
Why does rinsing the inside if the conical flask with deionised water improve titration’s accuracy 🚨
Ensures all the acid/alkali on the side if the flask is rinsed off
What’s concordance 🚨
Titres within 0.1cm of each other
Whats volumetric analysis
How titrations are used to accurately determine concs of unknown solutions
- need to know conc of volumetric solution (wch reacts with unknown)
- need to know volumes of solutions
Why do we need to accurately weigh out appropriate mass of solute (reweighing empty weigh boat after pouring solute into beaker)
It is how we calculate number of moles present in solution.
And hence then calculate conc.
- avoids overestimation of mass added
- as a result of some solid remaining in weigh boat
Why did we break up solid with stirring rod
Ensures all solid dissolves
It increases SA wch speeds up dissolution
Why did we use
- funnel to pour solution into volumetric flask
- rinse glass rod into volumetric flask
- and rinse inside beaker many times and pour washings into flasks
Ensures all dissolved solute ends up in volumetric flask
Why is base of meniscus on the mark
Ensures accurate measure of volume of solution made
Narrow neck design of volumetric flask minimises error with formation of meniscus
Why did we put lid in volumetric flask and invert 10 times
So solution is homogeneous (conc throughout solution is same)
Pipettung out aliquots (known volumes) from any part of solution wont affect conc of solution removed
Molar mass
Mass(g)/mol
How to find mass of an atom / ion
Get atomic mass (/1000 to kg)
Then divide by avagadros
How do you make volumetric solutions
Titrations are used to determine concentration of unknown solutions
—> this is volumetric analysis
— Done by preparing a volumetric solution and then carrying out
A reaction between a known volume of that and the unknown solution
– the key to determining the conc of the unknown solution
– is knowing conc of volumetric solution and measuring both solution volumes accurately
To do this..
1. Weigh appropriate masses of solute
- find mass of an empty weigh boat
- add appropriate mass of solute to the boat and reweigh
- empty solute into 250cm3 beaker
- reweigh empty weigh boat
- Dissolve all solute in beaker by adding
75–100cm3 of distilled water and stir with stirring rod (break up solid) - Pour solution into volumetric flask with funnel
Rinse inside beaker and pour into flask (dont add over 250cm3) - Carefully make solution up to the mark using a clean pipette
Ensuring meniscus is on mark - Place lid on volumetric flask and invert 10 times
