Acids And Bases Flashcards
Define a base according to Brønsted-Lowry theory
Proton acceptor
Define an acid according to Brønsted Lowry
Proton donor
Define a conjugate acid-base pair according to Brønsted Lowry
An acid and base species that differ only by one proton
What is the conjugate acid and conjugate base of H2O?
acid - H30+
base - OH-
Define PH
-log10[H+]
In terms of hydrogen ions, account for the difference in PH values of .1M of hydrochloric acid and .1M of sulfuric acid
HCL is monobasic and therefore each molecule of HCL contains one H+
Sulfuric acid is dibasic and therefore each molecule of sulfuric acid contains two H+
In terms of hydrogen ions, account for the difference in PH values between .1M of hydrochloric acid and .1M of methanoic acid
HCL - is monobasic and therefore in each HCL molecule there is one H+
Methanoic acid is dibasic and therefore in each methanoic acid molecule there are two H+ ions
Explain the selection of ur graph in reference to your PH curve
Colour change coincides with sharp rise on graph
Distinguish between a strong acid and a weak acid in terms of Arrhenius and Brønsted lowrry
Arrhenius
Strong- dissociates completely to give H+ ions
Weak - dissociates slightly to give H+ ions
Brønsted Lowry
Strong acid - readily transfers protons
Weak acid - transfers protons less readily
Define Kw
[H+] [OH-]
What is an Arrhenius acid?
Neutral molecule that dissociates in water to form hydrogen ions
What is an Arrhenius base?
A neutral molecule that dissociates in water to form hydroxide ions
State one limitation of the PH scale
Suitable only for dilute solutions
Only valid in 1-14 range
How do you calculate initial concentration with Ka from graph
Use first PH and do from there
Make use of PH graph to deduce the volume of a solution required for neutralisation
Where it goes vertical
Draw a ruler
Refer to PH curve to justify answer of indicator from graph
Range of indicator coincides with vertical part of PH
HNO2 + H2O - H3O+ + NO2-
Explain how the h3O+ / H+ concentration confirms that nitrous acid is a weak acid
Concentration of hydronium ions is lower than .2M of nitric acid which means it only slightly dissociates
HIn is a weak acid which dissociates as follows in water
HIn H+ and In-
Green purple
State and explain the colour observed when a few drops of the solution of the indicator is added to NaOH solution
Purple - hydroxide ions are removed by hydrogen ions which abuse reaction to shift forward
How do you find the conjugate base of an acid?
- 1 hydrogen
- 1 charge
How do you find the conjugate acid of a base?
+1 hydrogen
+1 charge
Distinguish between a weak base and strong base in terms of Arrhenius and Brønsted Lowry
Arrhenius -
Strong - dissociates completely to give off hydroxide ions
Weak - dissociates slightly to give off hydroxide ions
Brønsted-Lowry
Strong - accepts protons more readily/good proton acceptor
Weak - accepts protons less readily / bad proton acceptor
What is the conjugate base of
i) sulfuric acid
ii) weak acid HA
And which of these bases are stronger?
i) HSO4-
ii) A-
A- because it’s conjugate acid is weak
Explain by giving a balanced equation for its dissociation in water that the conjugate base of sulfuric acid is itself an acid
HSO4- + H20 - SO4^2- + H30+
The concentration in an aqueous solution of sodium hydroxide is .2g per litre. Calculate its PH
GET IN MOLES PER LITRE - DIVIDE BY MR OF 40 = .005
-log10(.005) = 2.3. BASE = 14-2.3 = 11.7
When do acids and bases conduct electricity?
When dissolved in water
What are the limitations of the Arrhenius theory?
It only refers to acids and bases dissolved in water
What is the advantage of the Brønsted-Lowry theory
Not restricted to water based acids and bases
It allows gaseous reactions
It allows for the amphoteric nature of water [can act as an acid and as a base]
What occurs when acids react with water itself?
H+ ion creates a dative bond with the lone pairs on the water’s oxygen atom to from H30+
What is an alkali?
It’s a base that dissolves in water
If there’s a strong acid, is the conjugate bass weak or strong?
Weak
The stronger the acid, the weaker the conjugate base
Identify the conjugate acid-base pairs in the following reaction
HNO3 + H20 = H30+ + NO3-
HNO3 AND NO3- -> bc they differ from each other by a H+
H20 and H30+ -> differ by h+
Give the equation/expression for when water self ionises to a small extent
2H20 H30+ + OH-
Explain the term monobasic acid
An acid that has one displaceable H atom per molecule
What is an acid-base indicator?
A weak base or acid which in a solution has one colour at a particular PH and a different colour at a different PH
i) Write an equation for the reaction that takes place between a strong monobasic acid and water
ii) Write also an equation for the reaction takes place when a weak monobasic acid accepts a proton from the strong monobasic acid HA
i) HA + H2O -> H30+ + A-
ii) HA + HX -> H2X+ + A-
If u have a weak acid indicator what occurs in equilibrium
i) added to an acid
ii) added to base
System will shift to left due to high h+ concentration
System will shift to right due to the OH- ions consume the H+
If u have a weak base indicator what occurs in equilibrium
i) added to a base
ii) added to an acid
i) equilibrium shifts to left in excess OH-
ii) equilibrium shifts right as OH- are consumed by H+
The value of Kw at 25 degrees celsius is 1.0 x 10^-14
Show that the PH of pure water is 7.0 at 25 degrees Celsius
[H+] = [OH-] [H+]2 = 1.0 x 10^-14 square root both sides H+ = 1.0 x 10^-7 -log10(1.0 x 10^-7) 7
Explain how an acid-base indicator which is itself a weak acid + may be represented as HX, functions
It is represented as
HX -> H+ + X-
In an acid, equilibrium shifts to the left as there is more of a concentration of H+ and gives the molecules colour
In a base, the equilibrium shifts to the right as OH- ions are consumed by H+ which gives the colour of molecules
Limitations of the PH scale
Only works well with dilute aqueous solutions
How do u get to M/L from 4.5g per 100cm^3
4.5 x 10 = 45g per litre
Divide by mr = MOLAR
Give examples of strong acids
HCl, H2SO4, HNO3
Give examples of weak acids
CH3COOH, HCOOH
Give examples of strong bases
NaOH, KOH, Ca(OH)2
Give examples of weak bases
NH3 + NH4OH
What indicator is used for strong acid and a strong base
Any indicator
What indicator is used for a strong acid and weak base?
Methyl orange [red-yellow] [3-7]
What indicator is used for a weak acid and strong base
Phenolphthalein [colourless-pink]
[7-10]
What indicator is suitable for a weak acid and weak base
No suitable indicator
The indicator changes colour in the PH range 3.7-5.7. State a type of acid-base titrations for which it would be suitable and justify your answer
Strong acid - weak acid
PH range of indicator lies within PH range of these titrations and give sharp end point
Explain how an acid-base indicator represented by XOH which itself is a weak base, functions
Addition of acid removes the OH- ions as equilibrium shifts to right and colour B dominates
Addition of base increases concentration of OH- ions on RHS side of equation, shifting equilibirum to left and colour A dominates
What colour is formed when phenolphtalein is added to
i) acid
ii) base
i) Colourless
ii) Purple/Pink
What colour is formed when methyl orange is added to
i) acid
ii) base
i) Red
ii) Yellow
What colour is formed when litmus is added to
i) acid
ii) base
i) Red
ii) Blue
What titration is used when indicator changes within range of PH 8-10
Weak acid v Strong base
