Properties of Water Flashcards
what are some properties of water
- Relatively high melting and boiling points
- High specific heat capacity
- High latent heat of fusion and high latent heat of
vaporisation
what is responsible for the properties of water
The polar O-H bond & the hydrogen bonding between
water molecules are responsible for the properties of
water.
What are group 16 hydrides?
O, S, Se, Te and Po. Each
of these elements can bond with hydrogen to form
compounds known as hydrides.
Why does the melting and boiling points of the other
group 16 hydrides increase as you move down the
group?
Dispersion forces increase in strength with increasing
mass. H2Po has a larger mass than H2S, hence has
stronger dispersion forces and high melting and boiling
points.
water is the smallest group 16 hydride
Each water molecule has the potential to form 4 hydrogen bonds with surrounding water molecules. These hydrogen bonds are stronger than the
intermolecular forces found between other molecules.
specific heat capacity
Amount of heat energy needed to increase the
temperature of a certain amount of substance by 1
oC
how is specific heat capacity calculated
= SHC(J g−1°C−1) × mass (g) × temperature change (°C)
= SHC × mass (g) × ΔT (°C)
= mCΔT
latent heat
Latent heat is the energy required to change a fixed amount of substance, usually 1 mole, from either a solid to a liquid or a liquid to a gas.
Latent heat of fusion
6 kjmol-1– heat needed to change 1 mole of
the substance from solid to a liquid at melting point
Latent heat of vaporisation
44.0 kjmol -1..heat needed to change 1
mole of the substance from liquid to a gas at boiling
point
latent heat calculation
q = n × L q = heat energy (kJ) n = amount (mol) L = latent heat value of fusion or vaporisation (kJ mol-1)
homogenous solution
when a substance dissolves in a liquid
dissolving
when the particles of the solvent and the solute form attractions with one another
soluble
solution where the solute and solvent cannot be distinguished from eachother
like dissolves like
rule where polar substances dissolves only polar substances and non-polar substances dissolves only non-polar substances can be used to predict if something will dissolve in a solvent.
Why are the solvent properties of
water important?
- transport nutrients
- cleaning, drinking fluids
- fertiliser and medication
Ways water acts as a solvent
- Highly polar covalent molecules can ionise in water then form ion-dipole attractions with water
- Ionic compounds can form ion-dipole attractions
with water
highly polar covalent molecules
h20 + HCl —-> H3O+ + Cl-
ionic compound insoluble generalisations
Ionic compounds that do not readily dissolve in water are insoluble in water.
This means a greater amount of energy is needed to separate the ions from the lattice.
Often increasing the temperature of water increases the solubility of ionic compounds.
SNAPE
Sodium(Na+) Nitrate(NO3-) Ammonium(NH4+) Potassium(K+) Ethanoate (CH3COO-)
what is a precipitation
A precipitation reaction occurs if ions in a solution
combine to form an insoluble compound, this
substance is called the precipitate.
what is solubility
The solubility of a substance refers to the maximum amount of that substance that can be dissolved in a given quantity of solvent at a certain temperature (g per
100g).
crystallisation
When the temperature decreases and some solute comes out of solution to form crystals e.g. sugar is no longer dissolved in solution
solubility of gases
temperature increases = solubilty decreases
temperature decreases = solubilty increases
units of concentration (7)
Molarity – mol/L
- Concentration in g/L
- Concentration in mg/L or ppm
- Concentration in ppb
- Percentage by mass %(m/m)
- Percentage by volume %(v/v)
- Percentage mass/volume %(m/V)
Molar concentration
c=n/v
dilution
The process of adding more solvent to a solution
This results in the solute particles becoming more
widely spaced (e.g. cordial and water).
The concentration of solutes changes however the amount of solute remains the same.
relationship between intial and final concentration and volume
c1V1=c2V2
Gravimetric Analysis
Gravimetric analysis is a quantitative analysis of
substances based on mass.
It can be used to determine:
The water content of a substance (%)
The empirical and molecular formula of a substance
The amount of a particular ion in a substance by
forming a precipitate
