Unit 2) 3) Strong And Weak Acids And Bases

Question 1

Definition of strong and weak in chemistry (acids and bases)

Answer 1

• the words strong and weak have very different meaning : string acid is either concentrated or dilute depending on the number of moles of acid per litre of solution. Same applies to weak acid

Question 2

What is monoprotic / monobasic acid

Answer 2

• Any acid weak or strong that is capable of donating ONE hydrogen ion per molecule is termed monoprotic or monobasic
• an acid like sulphuric acid which can donate two hydrogen ions is called diprotic or dibasic
• hydrochloric , nitric and ethanoic acids are monoprotic

Question 3

What is the degree of ionisation and what does it determine

Answer 3

• the degree of ionisation is the ability of the non ionised acid molecule to produce hydrogen ions
• this is what determines whether an acid is classified as strong or weak
• the more an acid molecule tends to produce hydrogen ions the stronger it will be

Question 4

Definition of a strong acid

Answer 4

A strong acid is completely disassociated (ionised ) in aqueous solution

Question 5

What are strong lab acids

Answer 5

• hydrochloric acid (HCL)
• nitric acid (HNO3)
• sulfuric acid (H2SO4)

Question 6

What do these strong acids do when in water

Answer 6

They will fully dissociate (or ionise) in water. This means all the acid molecules become ions.

Question 7

What does a strong acidic solution consist of for example HCL and how can this be indicated through its equation

Answer 7

• an aqueous solution of hydrogen chloride (hydrochloric acid) will exist entirely as hydronium and chloride ions. No molecules or hydrogen chloride are present
• the arrow (in equation (HCL(g) + H20(l) —- > H+ (aq) + Cl- (aq) ) tells us that the reaction goes fully in the left to right direction

Question 8

Weak acid definition

Answer 8

A weak acid is only partially dissociated in aqueous solution. Weak acids are an equilibrium mixture of non ionised acid molecules, hydrogen ions and the conjugate base of the acid.

Question 9

Examples of weak acids

Answer 9

Most carboxyxilic acids eg ethanoic acid, methanoic acid , propanoic acid
Carbonic acid
Sulfurous acid
Weak acids are in data booklet

Question 10

What does a weak acid consist of and what indicates this in equation

Answer 10

• equilibrium mixture of non ionised acid molecules , hydrogen ions and the conjugate base of the acid
• ethanoic acid equation (CH3COOH(aq) + H2O___ (equilibrium arrow) ____ CH3COO-(aq) + H3O+ (aq) ) the equilibrium reversible arrow tells us that the dissociation process
• the position of the equilibrium lies well over to the left hand side so there will be very few hydronium ions and ethanoate ions present at equilibrium compared with a much larger number of ethanoic acid molecules
• we can also say that the value of the equilibrium constant K is much less than 1 for this reaction

Question 11

Acids such as carbonic , sulfurous and sulfuric have two hydrogen atoms per molecule that can become hydrogen ions are known as diprotic acids.
Their ionisation takes place in _____ steps. This is show in the data booklet

Answer 11

Two

Question 12

Strong and weak bases

Answer 12

The same definitions apply to strong and weak bases

Question 13

Definition and Examples of strong base

Answer 13

• strong base is completely ionised in aqueous solution I.e all the available hydroxide ions are released into solution.
  Examples include
  Oxides and hydroxides Of group (sodium hydroxide , potassium hydroxide )
  Oxides and hydroxides of Group 2 metals : barium hydroxide , barium oxide

Question 14

Definition and examples of a weak base

Answer 14

• a weak base is partially ionised in aqueous solution, only some of the molecules in a weak base are disassociated (ionised) when dissolved in water
• ammonia
• amino alkanes (amines)

Question 15

Position of equilibrium of weak base

Answer 15

• position of equilibrium lies well over to the left hand side (K<1)