Chapter 12: Water as a Solvent Flashcards
What is water often described as ..
“universal solvent”
WhAT IS water an excellent solvent for?
Many ionic and polar substances.
What does a readily dissolved substance depend on?
The polar nature of the water molecules
The nature of substance that dissolves in it.
What happens to molecular compounds mixed with water?
Some dissolve: Some Ionic compounds
Some are insoluble: Oil
What are the key factors of substances mixing with water?
- Biological
- Domestic
- Industrial situations
What is a precipitation reaction?
Two solutions reacts and produce an insoluble product
Solute meaning?
Substance that is dissolved
Solvent meaning?
Liquid that the solute is dissolved in
Together was does Solute & Solvent form?
A homogenous solution
uniform composition and properties throughout the whole solution.
Aqueous solution meaning?
Solvent is water..thats what the solution is called
Solubility meaning?
Extent to which SOLUTE can dissolve in a solvent.
What is Solubility also determined by?
Polar or non-polar nature of the solute and the solvent.
‘like dissolve like’ according to chemist mean
Strongly polar and ionic solutes tend to dissolve in polar solvents,
and non-polar solutes tend to dissolve in non-polar solvents
Process of dissolving also depend on..
Strength of the attraction or bonds between the solute particles, and
the attraction between the solvent particles and the new bonds that form between the solute and the solvent.
What is strength related to..?
Size of the energy required to break these bonds, compared to the energy released when the new attractions or bonds are formed.
Why is water an effective solvent?
Due to its polarity and ability to form hydrogen bonds.
What is energy used for?
Energy is required to break bonds
Energy is released when new bonds form
what happens when ionic compounds dissolve in water.
Cations attract to ned end of water and anions attract pos end of water.
If strong enough it breaks bonds between cation and anions,
compound dissolves
when ion dissolves in water its called
described as hydrated (contain water molecules within structure )
interaction between water ( any polar ) molecule and ion is
ion-dipole attraction
dissociation meaning
ions seperate when an ionic compound dissolves in a solvent
ions are surrounded by water molecules and cannot recombine
when ionic substances dissolve in water..
they dissociate (ions separates )
What if strength of ions are very strong?
The water molecules are unable to seperate the ions and the salt is insoluble
insoluble meaning
will NOT DISSOLVE
molecular meaning
group of atoms bonded together covalently
many do not dissolve in water
What is it called when molecules dissolve in water
Are highly polar, and described as dipoles
diff between polar and non-polar
non-polar: even distribution of charge
polar: uneven distribution of charge due to differences in electronegativity of the atoms
Polar molecules will dissolve in water cause they either (2)..
- Form ions in water
2. Form hydrogen bonds with water
Molecular compounds that ionise in water example
Why does it happen
HCl = hydrogen chloride ( highly polar )
Hydrogen ions combine with water = hydronium ions H3O+
Aqueous solution = hydrochloric acid
Attraction of the polar water molecule increase polarity of H-Cl bond … neg attracts H and so and pulls it away.
H atom covalently bonds with water ( aqueous )
Cl becomes aqueous ( the anion dissolves ) ( aqueous )
Both ions are hydrated and dorm ion-dipole interactions
Ionisation meaning
Process polar molecules compounds form ions when dissolved in water
What does highly polar molecular substances usually do?
They ionise in water when they dissolve.
What are the other molecular compounds that are soluble in water?
Molecules usually having hydrogen atom bonded to one F, O or N.. they dissolve by forming hydrogen bonding with water.
example: NH3 ammonia
Simplify four molecular compounds that dissolve in water.
- Ions : cation and anion
- Ionisation of molecular ( ion and hydrogen )
UNLESS THE BOND IS TOO STRONG LIKE AgCl - Hydrogen bond with F, O , N
- Alcohol molecules
Why are alcohol molecules soluble?
Form hydrogen bonding such AS with CH3OH
CH3-OH : methanol
the OH is highly polar + water = hydrogen bonding
however hydrogen bonding does not occur with CH3 due to small electronegativity / not very polar
so bond is like CH3-OH-0HH
Interesting about water & alcohol molecules interaction?
They take up less volume due to rearrangement of the molecules.
The volume of combined liquids is less than the sum of individual volumes.
Miscible meaning?
Two liquids able to be mixed and form a solution
Immiscible meaning?
Two substances are unable to form a homologous solution = form seperate layers
Example of Immiscible?
Oil and vinegar ( aqueous sol )
Oil is non polar molecules will only dissolve in non-polar solvents.
Why don’t polar and non-polar mix?
Non-polar molecules have weak dispersion forces and little energy required to seperate them.
WATER IS strongly bonded and tend to stick together and not interact with non-polar
Rules for polar and non-polar mixes (3)
Polar + polar = solution
non-polar + non-polar = solution
polar+ non-polar = suspension ( wont mix evenly )
What does carbon dioxide and water form?
Weakly acidic solution, so if soft drink have been open it loses carbon dioxide gas and result is flat taste.
What else influences the amount of has that dissolved in water?
Temperature
Increase = temp causes decreases the solubility of gases in liquids.
What does dissolved oxygen do in sea water?
The dissolved oxygen in sea water decreases as the temp increases
and this has significant implication for survival of seas organisms.
The solubility of gas in liquid decreases…
with increasing temperature
What is Electrical conductivity used to test?
What is useful to test the quantity ions formed in a solution
When does a substance conduct electricity?
Contains charged particles that are able to move
Does water conduct electricity? why
No, even though the molecules move freely in liquid state,
the covalent bonding in water molecules, results in a neutral molecules
pure water might sometimes conduct slightly
Why might pure water conduct electricity?
Slightly as it has small number of ions ( called self ionisation )
h2o(i) + h20(i) = h3o + oh-
double reversible arrows?
reaction simultaneously reacting in the forward direction and in the reverse direction.
electrolytes?
substances that produce ions when dissolved
conductivity of solutions can be used..
to compare the quantity of ions present
Why is water a good solvent for ionic compounds?
- Water molecule had polar arrangement pf oxygen and hydrogen atoms
- h = pos , o=neg charge….
- “disrupt attractive forces that hold the ionic compounds” together = dissolves it
what needs to be broken, to form ion-dipole interaction between ions and water
- ions must be broken
2. hydrogen bonds between water molecules
compare water and oil molecules
oil:
- non- polar
- weak dispersion forces
water:
- polar
- hydrogen bonding
when talking about molecules mention:
PSI
polarity, strength, intermolecular
polar or not
WEAK or STRONG
intermolecular : dipersion, dipole, or hydrogen
INTERACTION when dissolve in water
1: ionic compound
2: polar molecular compound
3: molecular compound:
1: ion-dipole interaction
2: ion-dipole interaction
3: hydrogen bonding
differences and similarities of gases
NH3 & HCl
BOTH: polar molecules
diff:
NH3 -> dissolves by forming hydrogen bonds with water
HCl -> H+ Cl- ——> ionises in water & ions become hydrates
precipitate
solid with low solubility formed in a liquid
solubility
grams of substance that will dissolve in an amount of solvent at a particular temperature
precipitation reaction
reaction where two solutions are mixed and a solid is formed
unreacted ions remained in the solution
why can’t water dissolve some substances
water is unable to dissociate the ionic lattice structure and they are therefore insoluble
what ion is most commonly soluble with water
nitrate!! NO3-
also K+ AND Na+
(aq) meaning
each ion is separated and has become surrounded by water molecules
spectator ions
ions that take no part in reaction but maintain electrical neutrality in a solution
step for balanced perception full equation
6 STEPS
- write reactants
optional ( write out products of each react ) - write out overall product ( switching )
- write skeleton equation ( reactant and products )
- Balance equation
- Use solubility table
- ADD STATE
ionic equations
equation without the spectator ions
a simpler equation, that only show the species that are formed or changed in a reaction
why does spectator ions not included in ionic equations?
because they remain in solution unchanged in the reaction
steps for writing ionic equations
- write the balance full chemical equation
- expand equations by dissociating all the SOLUBLE compounds into their free ions (( check if any substances such as acids or bases that react with water to produce ions ))
replace the formula by ions that are formed - cancel free ions that are uncharged in both sides of the equation ( spectator ions )
- write ions and formula remaining ( this is ionic equation )
- make sure equation is balanced in charge as well as in number of atoms and add symbols of state
- spectator ions are still in solution so write these with commas between
what happens to spectator ions in ionic equations?
they are omitted
precipitate remains in filter paper is called
residue
clear solution in the conical flask is
filtrate and contains spectator ions
solvent properties of water in biological contexts?
for body
rivers
plants
solvent properties of water in domestic contexts?
garden
beverages
personal care products
solvent properties of water in industrial contexts?
- water facilitates
- electrolysis reactions
- many chemicals
- manufacturing industries ( production of foods, medicines, fertiliser, detergents etc )
surfactants: contain molecules that are polar at one end and non-polar at the other. this allows to dissolve both water and pil. making suited cleaning agents where oil-and grease needs to be removed.
water benefit human body
transport nutrients ans soluble chemicals
around body to different cells
and carries waste
dissolved substances keep plants and fish alive in ponds
oxygen and carbon dioxide slightly soluble in water
fish can have oxygen for respiration
plants can have carbon dioxide for photosynthesis
how does water act as a solvent in a meal?
vinegar is ethanoic acid in water
soft drinks has dissolved sugar etc
why is it important that fertilisers are soluble in water
and problem it results
fertilisers can be sprayed on crops
solution absorbed through plant roots
excess nutrients can be washed into rivers, lakes etc
oxygen used in the decay process so fish are unable to survive.
how is water useful in the industrial production of materials?
chemicals can be diluted with water for reasons of safety.
disadvantages there is in the use of water in chemical industries?
contaminated water may be difficult to dispose
it might enter waterways
cause pollutions
what does oxygen and nitrogen have
non-polar gases have low solubility, but enough sustain aquatic life
an increase in pressure generally
decreases the solubility of a gas in liquid
what is not a characteristic of solution
solute particles can be separated by filtering
ions dissolve in water ..
pos ion goes with neg end
neg ions goes with pos end in ionic lattice
ion-dipole bonds are formed
ions are separated by water molecules that surround ions
ions are described as hydrated
as an ionic formular such as KCl (aq) , is mixed with water and is evaporated?
the solution will form solid crystals of potassium chloride.
Why can water have no net charge but have slight charges in different parts of the molecule?
The oxygen end is slightly negative and the hydrogen end is slightly positive
Fish need oxygen from which molecule?
O2
A water strider can skate along the top of a pond because:
hydrogen bonds result in water cohesion (surface tension)
Attractions between water molecules are called
Hydrogen bonds
Which of these would LEAST affect turbidity?
Salt
