Water Flashcards Preview

Chemistry > Water > Flashcards

Flashcards in Water Deck (55):

why is water important?

Water vapour reflects radiation
In cells- transport and reactions
Controls internal temp
Moisture in eyes and lungs etc.
Transport in oceans and rivers
Industry- cooling reactions and as a solvent


how does the water cycle work?

Evaporates from oceans.
Water vapour collects and condenses in clouds.
Precipitation returns water to the earth (usually a liquid).
Returns to ocean.


what is photosynthesis?

Convert water and carbon dioxide into glucose and oxygen.
With sunlight and chlorophyll.
Removes water vapour.


what is cellular respiration?

Occurs in all organisms
Converts glucose and oxygen back into water vapour and carbon dioxide


how does hydrogen bonding happen with water?

V-shaped molecule
Oxygen is more electronegative- permanent dipole.
Hydrogen bonding- strongest intermolecular bonding.
Between hydrogen and fluorine, nitrogen or oxygen.
Sets up a strong dipole.
Slightly positive end of molecule is attracted to slightly positive end of other (hydrogen bond).


why does water have high melting and boiling temperatures?

Higher than molecules of similar size.
A large amount of energy is needed to overcome hydrogen bonds.


what are the trends in the group 16 hydrides? why is water different?

Water, hydrogen sulfide, hydrogen selenide, hydrogen Telluride, hydrogen polonide
All are v-shaped and polar.
Boiling points are reflection of size and forces between molecules. Higher intermolecular, high BT.
Water is the only one with hydrogen bonding so has higher melting and boiling points.


why does water expand on freezing?

Each water molecule from hydrogen bonds with four other molecules.
In liquid form, this structure is lost and molecules are closer.
Ice is therefore less dense than water.


what is the measure of heat capacity?

A measure of its ability to absorb and store heat energy.
how much energy can be absorbed before temperature increases.


what is specific heat capacity?

A measure of the amount of energy needed to increase the temperature of a certain amount of substance (usually 1g) by 1 degree.


what is water's specific heat capacity?

Water- 4.18Jg^-1 degrees C^-1


why does water have a relatively high specific heat capacity?

Water’s is high due to hydrogen bonding- can store more energy without heating up.


how is heat energy calculated and what does everything stand for?

Heat energy = specific heat capacity x mass x temperature change

q = C x m x AT

q- heat energy (joules)
C- specific heat capacity (Jg-1degree C-1)
m- mass (g)
AT- temperature change (degree C -1)- Tf-Ti


what is latent heat?

Energy needed to change the sate of a fixed amount of substance (usually one mole).
Temperature remains constant until all substance has changed.


what is latent heat of fusion?

the amount of energy required to change 1 mole of substance from solid to a liquid as its melting point. 6.0KJ mol-1 in water


what is latent heat of vaporisation?

the amount of energy to change 1 mole of a substance from a liquid to as gas at its boiling point. 44.0KJ mol-1 in water


why does water have higher latent heat than others?

Latent heat of water is higher than others- hydrogen bonding.


how is heat energy in latent heat calculated?

Heat energy = amount of substance x latent heat value

q = n x L

q- heat energy in KJ
n- amount (mol)
L- latent heat of fusion or vaporisation (KJ mol -1)


why is water not found in its pure form?

substances dissolve.


what makes up a solution?

Solute + solvent = solution


what are characteristics of solutions?

Homogenous: solute and solvent cannot be distinguished.
Dissolved particles are too small too see.
The amount of dissolved solute can vary from solution to solution.


what is a dissolution?

process of one substance dissolving in another.


what is miscible?

when both substances are liquid.


how does dissolution occur?

Particles of solute separate.
Particles of solvent separate.
Solute and solvent particles are attracted.


how does dissolving take place? what conditions are there?

Dissolving takes place if the particles have a strong enough attraction.
Like dissolves in like. Polar and polar, non-polar and non-polar.
Seen in biological, domestic and industrial contexts.


how do polar covalent substances dissolve in water? HB

Hydrogen bonds between molecule break, hydrogen bonds in water break, new hydrogen bonds from between substance and water.
Larger the non-polar fraction, the less soluble.


how do polar covalent molecules dissolve? ionise

Molecules break apart.
The polar bonds are so polar that this occurs.
Hydrated: ions surrounded by water molecules.
Hydronium (H3O+)
Water is a reactant (not on arrow).
Ionisation: process of molecules breaking apart and being attracted to water.


how do ionic compounds dissolve?

Ionic bonds are broken.
Hydrogen bonds in water are broken.
Ion-dipole attraction is formed between ions and water.
Dissociation: ions are freed.
Water is not a reactant (on the arrow).


when are things insoluble?

energy required to break apart is greater than energy produced when they are hydrated- stay together.



SNAPE rule: sodium (all group 1), nitrate, ammonium, potassium and ethanoate ions are soluble.


what is a precipitation reaction? what happens? what is another name?

When a precipitate forms when two solutions are mixed.
Positive ions in one solution are attracted to negative ions in another.
The clyster to form crystals.
Double replacement reaction.


what is solubility?

maximum amount that can be dissolved in a substance at a given temp. measured in g/100g



no more can dissolve at a given temperature. on



less than max is dissolved at a given temperature. under


what happens when saturated solutions are cooled?

some falls out



carefully cooled and crystals do not precipitate, more is dissolved than possible, unstable- add a seed crystal, it falls out. above


as temp increases...

solubility usually increases


what is crystallisation?

Evaporate water from unsaturated solution, it will become saturated.
More evaporation: crystals fall out.


what does fast evaporation cause? slow evaporation?

Evaporate water from unsaturated solution, it will become saturated.
More evaporation: crystals fall out.


what does solubility of gases depend on?

Solubility of gas depends on temp and pressure of gas.
Temp increases: solubility decreases.
Pressure increases: solubility increases.


what is concentration?

description of the relative amounts of solute and solvent present.



loss of solute compared to solution.



little solute to solvent.


concentration in grams per litre

Concentration (g/L) = mass of solute (g)/volume of solution (L)


concentration in ppm

Concentration (ppm) = mass of solute (mg)/mass of solution (kg)
Mass in 1000000g of solution


concentration of mg per L

Concentration (mg/L) = mass of solute (mg)/volume of solution (L)
Same as mg/L


concentration in ppb?

Concentration (ppb) = mass of solute (micrograms) / mass of solution (Kg)


percentage by mass (%w/w)

Concentration (%w/w) = (mass of solute / mass of solution) x 100
Mass of solute per 100g of solution.
Units of mass must be the same.


Percentage by volume (%v/v)

Concentration (%v/v) = (volume of solute / volume of solution) x 100
Volume per 100ml of solution.
Units must be the same.


Percentage by weight/volume (%w/v or %m/v)

Concentrate (%w/v) = (mass of solute / volume of solute) x 100
Mass of solute per 100ml of solution.
Units must be grams and mLs.


what is molar concentration?

Amount in mol of solute per volume.


how much mol does 1M of solution contain?

1M solution contains one mol of solute dissolved in each litre.


formula for concentration?

n = c x V

N- amount in mol
C- concentration in mol/L
V- volume in litres


what is dilution?

Process of adding more solvent to a solution.
When diluted, there is the same amount of solute but particles are more widely spread.


what us the formula for dilution?

c1V1 = c2V2

C1- initial concentration
V1- initial volume
C2- final concentration
V2- final concentration
Must have same units