Acids And Bases

Question 1

Define a base according to Brønsted-Lowry theory

Answer 1

Proton acceptor

Question 2

Define an acid according to Brønsted Lowry

Answer 2

Proton donor

Question 3

Define a conjugate acid-base pair according to Brønsted Lowry

Answer 3

An acid and base species that differ only by one proton

Question 4

What is the conjugate acid and conjugate base of H2O?

Answer 4

acid - H30+

base - OH-

Question 5

Define PH

Answer 5

-log10[H+]

Question 6

In terms of hydrogen ions, account for the difference in PH values of .1M of hydrochloric acid and .1M of sulfuric acid

Answer 6

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+

Question 7

In terms of hydrogen ions, account for the difference in PH values between .1M of hydrochloric acid and .1M of methanoic acid

Answer 7

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

Question 8

Explain the selection of ur graph in reference to your PH curve

Answer 8

Colour change coincides with sharp rise on graph

Question 9

Distinguish between a strong acid and a weak acid in terms of Arrhenius and Brønsted lowrry

Answer 9

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

Question 10

Define Kw

Answer 10

[H+] [OH-]

Question 11

What is an Arrhenius acid?

Answer 11

Neutral molecule that dissociates in water to form hydrogen ions

Question 12

What is an Arrhenius base?

Answer 12

A neutral molecule that dissociates in water to form hydroxide ions

Question 13

State one limitation of the PH scale

Answer 13

Suitable only for dilute solutions

Only valid in 1-14 range

Question 14

How do you calculate initial concentration with Ka from graph

Answer 14

Use first PH and do from there

Question 15

Make use of PH graph to deduce the volume of a solution required for neutralisation

Answer 15

Where it goes vertical

Draw a ruler

Question 16

Refer to PH curve to justify answer of indicator from graph

Answer 16

Range of indicator coincides with vertical part of PH

Question 17

HNO2 + H2O - H3O+ + NO2-

Explain how the h3O+ / H+ concentration confirms that nitrous acid is a weak acid

Answer 17

Concentration of hydronium ions is lower than .2M of nitric acid which means it only slightly dissociates

Question 18

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

Answer 18

Purple - hydroxide ions are removed by hydrogen ions which abuse reaction to shift forward

Question 19

How do you find the conjugate base of an acid?

Answer 19

• 1 hydrogen

- 1 charge

Question 20

How do you find the conjugate acid of a base?

Answer 20

+1 hydrogen

+1 charge

Question 21

Distinguish between a weak base and strong base in terms of Arrhenius and Brønsted Lowry

Answer 21

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

Question 22

What is the conjugate base of
i) sulfuric acid
ii) weak acid HA
And which of these bases are stronger?

Answer 22

i) HSO4-
ii) A-

A- because it’s conjugate acid is weak

Question 23

Explain by giving a balanced equation for its dissociation in water that the conjugate base of sulfuric acid is itself an acid

Answer 23

HSO4- + H20 - SO4^2- + H30+

Question 24

The concentration in an aqueous solution of sodium hydroxide is .2g per litre. Calculate its PH

Answer 24

GET IN MOLES PER LITRE - DIVIDE BY MR OF 40 = .005

-log10(.005) = 2.3. BASE = 14-2.3 = 11.7

Question 25

When do acids and bases conduct electricity?

Answer 25

When dissolved in water

Question 26

What are the limitations of the Arrhenius theory?

Answer 26

It only refers to acids and bases dissolved in water

Question 27

What is the advantage of the Brønsted-Lowry theory

Answer 27

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]

Question 28

What occurs when acids react with water itself?

Answer 28

H+ ion creates a dative bond with the lone pairs on the water’s oxygen atom to from H30+

Question 29

What is an alkali?

Answer 29

It’s a base that dissolves in water

Question 30

If there’s a strong acid, is the conjugate bass weak or strong?

Answer 30

Weak | The stronger the acid, the weaker the conjugate base

Question 31

Identify the conjugate acid-base pairs in the following reaction HNO3 + H20 = H30+ + NO3-

Answer 31

HNO3 AND NO3- -> bc they differ from each other by a H+ | H20 and H30+ -> differ by h+

Question 32

Give the equation/expression for when water self ionises to a small extent

Answer 32

2H20 H30+ + OH-

Question 33

Explain the term monobasic acid

Answer 33

An acid that has one displaceable H atom per molecule

Question 34

What is an acid-base indicator?

Answer 34

A weak base or acid which in a solution has one colour at a particular PH and a different colour at a different PH

Question 35

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

Answer 35

i) HA + H2O -> H30+ + A- | ii) HA + HX -> H2X+ + A-

Question 36

If u have a weak acid indicator what occurs in equilibrium i) added to an acid ii) added to base

Answer 36

System will shift to left due to high h+ concentration | System will shift to right due to the OH- ions consume the H+

Question 37

If u have a weak base indicator what occurs in equilibrium i) added to a base ii) added to an acid

Answer 37

i) equilibrium shifts to left in excess OH- | ii) equilibrium shifts right as OH- are consumed by H+

Question 38

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

Answer 38

``` [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 ```

Question 39

Explain how an acid-base indicator which is itself a weak acid + may be represented as HX, functions

Answer 39

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

Question 40

Limitations of the PH scale

Answer 40

Only works well with dilute aqueous solutions

Question 41

How do u get to M/L from 4.5g per 100cm^3

Answer 41

4.5 x 10 = 45g per litre | Divide by mr = MOLAR

Question 42

Give examples of strong acids

Answer 42

HCl, H2SO4, HNO3

Question 43

Give examples of weak acids

Answer 43

CH3COOH, HCOOH

Question 44

Give examples of strong bases

Answer 44

NaOH, KOH, Ca(OH)2

Question 45

Give examples of weak bases

Answer 45

NH3 + NH4OH

Question 46

What indicator is used for strong acid and a strong base

Answer 46

Any indicator

Question 47

What indicator is used for a strong acid and weak base?

Answer 47

Methyl orange [red-yellow] [3-7]

Question 48

What indicator is used for a weak acid and strong base

Answer 48

Phenolphthalein [colourless-pink] | [7-10]

Question 49

What indicator is suitable for a weak acid and weak base

Answer 49

No suitable indicator

Question 50

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

Answer 50

Strong acid - weak acid | PH range of indicator lies within PH range of these titrations and give sharp end point

Question 51

Explain how an acid-base indicator represented by XOH which itself is a weak base, functions

Answer 51

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

Question 52

What colour is formed when phenolphtalein is added to i) acid ii) base

Answer 52

i) Colourless | ii) Purple/Pink

Question 53

What colour is formed when methyl orange is added to i) acid ii) base

Answer 53

i) Red | ii) Yellow

Question 54

What colour is formed when litmus is added to i) acid ii) base

Answer 54

i) Red | ii) Blue

Question 55

What titration is used when indicator changes within range of PH 8-10

Answer 55

Weak acid v Strong base