Water Flashcards
Shape and structure of water molecule
Shaped like wide V
Two hydrogen atoms joined to an oxygen atoms by single covalent bond
Water molecule’s polarity
water is a polar molecule because oxygen is more electronegative than hydrogen so the shared pair of electrons pair spend more time near oxygen forming polar covalent bond
Overall charge of water molecule
Oxygen contains two regions of partial negative charge and hydrogen has a region of partial positive charge
Which type of bond is held two water molecules together?
Hydrogen bond
Six properties of water
1.Polarity
2.Excellent solvent
3.High heat capacity
4.Cohesion(high surface tension)
5.Adhesion
6.Low density when frozen
How water can be excellent solvent?
As water molecule is polar molecule,it can dissolve poler molecules and ions due to its ability to form ion-dipole and dipole-dipole interactions
What is cohesion?
Attraction between water molecules
What is adhesion?
Attraction between water molecules and other substances
What is surface tension?
A measure of how difficult it is to stretch or break the surface of a liquid
Why water molecules have high surface tension?
At the interface between water and air,water molecules are hydrogen-bonded to one another to water molecules below but not to the above air
What is kinetic energy?
The energy of motion
The faster a molecule moves,the greater its kinetic energy
What is thermal energy?
The kinetic energy associated with random movements of atoms and molecules
What is difference between thermal energy and temperature?
Thermal energy of a body of matter is the total kinetic energy that depends on matter’s volume
Temperature is the average kinetic energy of molecules in body without the volume of the body
What will happen when two objects with the different temperature are brought together?
Thermal energy passes from warmer objects to cooler object until the two are at the same temperature
What is heat?
Thermal energy in transfer from one body of matter to another
Units of heat
Calorie(cal)-amount of heat it takes to rise the temperature of 1g of water by 1 C
Kilocalorie(kcal)-1000cal-amount of heat required to raise the temperature of 1kg of water by 1•C
Joule
Specific heat
The amount of heat that must be absorbed or lost for 1g of substance to change its temperature by 1•C
A measure of how well a substance resists changing its temperature when it absorbs or releases heat
Water’s specific heat
1cal/(g •C) i.e.1 cal of heat is required for 1g of water to change its temperature by 1•C
water resists changing its temperature when it absorbs or releases heat
Water’s high specific energy compared to ethanol
Water-1cal/g•C
Ethanol-0.6cal/g•C
What is heat of vaporization?
The quantity of heat of a liquid must absorb for 1 g of liquid to be converted from liquid to gaseous state
Do water have high heat vaporization?
Yes
Density of ice vs liquid water
Ice has lower density than liquid water because of crystalline lattice structure of ice
What is water density at 4•C and above?
At 4•C,like other liquids water expands as it warms and water contracts as it cools
Water density at below 4•C-0•C
Water begins to freeze because more and more of its molecules are moving too slowly
At 0•C,the molecules is locked into crystalline lattice structure
what is solvent?
Dissolving agent of a solution
What is solute?
The substance that is dissolved in solution
What is solution?
A liquid that is completely homogeneous mixture of two or more substances
What is aqueous solution?
The solute is dissolved in water
water is the solvent in aqueous solution
Which solutes can water dissolve?
Ionic molecules and polar molecules
Hydrophilic molecules
Molecules that have affinity for water (ionic and polar molecules)
water-loving molecules
All hydrophilic molecules are dissolved in water.True or false?
False,substances can be hydrophilic without actually dissolving
Eg.cotton
Hydrophobic molecules
Substances that do not have an affinity for water (nonionic and non-polar molecules)
water-hating molecules
What is molarity?
Molarity is the unit of concentration
The number of moles of solute per liter of solution
What is mole?
A mole is a certain number of molecules of a substance.
What is molecular mass?
The mass of a mole of substance in grams
Water dissociation
When two water molecules are connected by a hydrogen bond ,hydrogen ions(H+) is transferred to one molecule to another forming Hydronium ions(H3O+) and the molecule that lost hydrogen ion becomes hydroxide ion(OH-)
It is the reversible reaction and reaches at a state of equilibrium
What is the concentration of H+ and OH- in pure water?
same concentrations
What is acid?
A substance that increases the hydrogen ion concentration of a solution
HCl——->H+ +Cl-
What is base?
a substance that reduces the concentration of H+ ion
Some bases reduce H+ conc directly by accepting hydrogen ions and
other bases reduce reduce H+conc indirectly by dissociating to form OH- ions
What is acidic solution?
Solution with higher concentration of H+ ions than OH- ions
acidic solution have pH value of less than 7
What is basic solution?
A solution with higher concentration of OH- ions than H+ions
basic solutions have pH value of greater than 7
How strong acid and strong base dissociate in water?
Completely dissociate
Eg.HCl and NaOH
What is weak acid and weak base?
The substance that dissociates partially in water
In which temperature,the product of [H+][OH-] concentration is constant?
25 degree Celcius
In 25 degree Celcius,the product of [H+][OH-] concentration is constant.What is tha value of this constant?
[H+][OH-]=10 *-14
So [H+]=10* -7 and [OH-]=10* -7
When enough acid is added to the solution to increase [H+] to 10*-5M ,what is [OH-] value?
10* -9 M
When enough base is added to the solution to increase [OH-] to 10*-4M ,what is [H+] value?
10* -10 M
pH and [H+] relation
pH=-log[H+]
pH decreases as H+ concentration increases
pH 1 example
Battery acid
pH 2 example
Gastric juice(HCl in stomach)
Lemon juice
pH 3 example
Vinegar
Wine
Cola
pH 4 and 5 example
Tomato juice
Beer
Black coffee
pH 5.5 example
rain water
pH 6 example
Urine
pH 7 example
Saliva
Pure Water
Human blood
Tears
pH 8 example
seawater
inside small intestine
pH 10.5 example
Milk of magnesia
pH 11.5 example
Household ammonia
pH 13 example
Household bleach
pH 13-14 example
Oven cleaner
pH value of blood
7.4
How strong acid effect on pH value of pure water?
if 0.01 mol of strong acid is added to 1L of pure water,pH drops from 7.0 to 2.0
If 0.01mol of strong acid is added to 1L of blood,how the pH value change?
pH value decrease only 7.4 to 7.3
Why does tha addition of strong acid of acid have so much less effect on pH of blood than it does on pH of pure water?
The presence of buffers in biological fluids to maintain constant pH despite the addition of acid or bases
What is buffer?
a substance that minimizes changes in the concentration of H+ and OH- in a solution
Most buffer solutions are weak acid and its corresponding base,which combine reversibly with H+ ions
Eg.Carbonic acid H2CO3
Acetic acid CH3COOH
How carbonic acid dissociate as buffer solution?
Carbonic acid dissociates into a bicarbonate ions(HCO3-) and hydrogen ions(H+)
The reaction is reversible and is in equilibrium state
What will happen if the H+ concentration in blood begins to fall?
when [H+] fall in blood, pH of blood will rises
So more carbonic acid dissociates and replenishes H+ ions
What will happen if the H+ concentration in blood begins to rise?
when [H+] rise tha pH of the blood drops
So HCO3- and H+ ions will react to form more carbonic acid(H2CO3)
Is that correct most buffers are acid-base pairs?
Yes
