water and solutions

Question 1

effect of hydrogen bonding on water properties

Answer 1

high melting point and boiling point
expansion of water upon freezing
high latent heat
high specific heat capacity
capillary action
ability of water to dissolve other substances

Question 2

why does temp stay the same during a phase change?

Answer 2

the energy put in is used to break the hydrogen bonds between the molecules, not used to vibrate and move the molecules

Question 3

why does water have high mp and bp?

Answer 3

each water molecule capable of making four hydrogen bonds to other molecules
strength and number of these bonds gives rise to water’s high melting and bp
a significant amount of heat energy is needed to disrupt all of the H bonds

Question 4

why does water expand upon freezing?

Answer 4

open, hexagonal crystalline lattice of ice pushes the water molecules further apart that occurs in the liquid state, expanding the structure

the same number of molecules will occupy a larger space so ice has a lower density than water

Question 5

latent heat of fusion

Answer 5

the energy required to convert one mole of a substance from a solid to a liquid, at its melting point.
water = 6 kJ/mol

Question 6

latent heat of vaporisation

Answer 6

the energy required to convert one mole of a substance from a liquid to a gas, at its boiling point.
water = 44 kJ/mol

Question 7

specific heat capacity?

Answer 7

the amount of energy required to raise the temperature of one gram of a substance by one degree celsius

provides a measure of the substance’s capacity to absorb and store heat energy

Question 8

why does water have high shc?

Answer 8

because of its capacity for hydrogen bonds to be broken, allowing molecules to move more freely, and to reform

water shc = 4.18 J per gram per degree celsius

Question 9

physical properties of water

Answer 9

1. polar compound made of discrete molecules
2. freezes at 0 deg celsius and boils at 100 deg celsius
3. ice is less dense than water
4. is the universal solvent
5. liquid water evaporates at all temperatures above 0 degrees celsius

Question 10

solubility rules

Answer 10

Na+, K+, NH4+, NO3-, CH3COO- (SNAPE)
Cl-, Br- and I- …. except with Ag+ and Pb2+
SO42- …. except with Pb2+ or Ba2+

Question 11

insolubility rules

Answer 11

O2-, S2-, CO32-, PO43- …. except with Na+, K+, NH4+
OH- ….. except with Na+, K+, NH4+, Ba2+, Ca2+

Question 12

define saturated solution

Answer 12

a solution in which no more solute can be dissolved at that temperature

Question 13

define unsaturated solution

Answer 13

a solution that contains less solute than is needed to make a solution saturated at that temperature

Question 14

supersaturated solution

Answer 14

an unstable solution that contains more dissolved solute than in a saturated solution. this may arise when the temperature of a saturated solution decreases

Question 15

what is crystallisation

Answer 15

when solid crystals form as the temperature decreases and the solute can no longer remain dissolved (the solute crytallises out of the solution). the slower the cooling, the bigger the crystals that form

Question 16

define solubility

Answer 16

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

Question 17

solubility curves

Answer 17

each point on the line = saturated solution
any point below the line = undersaturated solution
any point above the line = super saturated solution

Question 18

define solution

Answer 18

an evenly distributed mixture of atoms, molecules or ions including a liquid solvent and one or more solutes

Question 19

define solute

Answer 19

a substance which is dissolved in a solvent

Question 20

define solvent

Answer 20

the primary component of a solution, in which one or more solutes are dissolved

Question 21

define miscible

Answer 21

a description of two liquids which mix together readily

Question 22

suspension?

Answer 22

where a solid substance is dispersed in a solvent, but not dissolved. the solid particles are distinguishable from the solvent particles

Question 23

latent heat calculations

Answer 23

q=nl
n=number of mol of substance
l=latent heat of fusion or vaporisation q=amount of energy required, kj/mol

Question 24

specific heat capacity calculation

Answer 24

q=mcAt
c=specific heat capacity, water=4.18
m=mass of substance in grams
At=change in temp in celcius or kelvin

Question 25

what strong intermolecular bonds can water form with others?

Answer 25

-dipole dipole forces with polar molecules
-hydrogen bonds with substances containing NOF groups
-ion dipole forced with ions and charged groups on molecules

Question 26

what are ion dipole forces

Answer 26

forces of attraction between a positive ion w. neg pole of dipole OR neg ion w positive pole of dipole

Question 27

what is an ionic equation

Answer 27

shows the formation of a new product = precipitate, omitting the spectator ions - they do not participate in the reaction

Question 28

define molarity

Answer 28

the moles of solute per litre f solution
units = mol/L

n=CV

Question 29

unit conversions - changing prefix

Answer 29

eg. from grams to milligrams, g->mg
value x 10^(initial prefix - final prefix)
eg. g-> mg = 10^(0-(-3))

Question 30

ppm

Answer 30

parts per million
mass of solute in milligrams/volume of solution in litres
ppm=mg/L (IN WATER)

OR ppm=micrograms/grams

Question 31

equations

Answer 31

n=cv
M=CV (don’t forget)

Question 32

%w/w

Answer 32

concentration of a dissolved solute with effective units grams/100g

Question 33

%w/v

Answer 33

concentration of a dissolved solute with effective units g/100ml

Question 34

%v/v

Answer 34

concentration of a dissolved liquid solute with effective units mL/100mL

Question 35

define precipitate

Answer 35

a solid formed when two dissolved compounds react to form an insoluble ionic compound