Acids and Bases

Question 0

What is an acid? According to Arrhenius?

Answer 0

A substance which dissociates in water and forms H+ ions

e.g. HCl (aq) -> H+ + Cl-

Question 1

Give the names and formulae of 3 common lab acids

Answer 1

1. Hydrochloric acid -> HCl
2. Sulfuric acid -> H2SO4
3. Nitric acid -> HNO3

Question 2

According to Arrhenius what is the difference between a strong and weak acid?

Answer 2

Strong Weak
These acids almost completely These acids only slightly/
dissociate and form H+ ions partially dissociate in water and
in water. Eg. HCl, H2SO4, form H+ ions e.g. CH3COOH
HNO3
Form weak conjugate bases. Form strong conjugate bases

Question 3

Give to limitations to Arrhenius definition

Answer 3

1. Restricted his definition of an acid to aqueous solutions i.e. a substance can only behave as an acid when in water
2. Now known a H+ have an independent existence in water ( too small )

Question 4

What is an acid according to Bronsted Lowry?

Answer 4

An acid proton donor

Question 5

What is the difference between a strong and weak acid according to Bronsted Lowry?

Answer 5

Strong. Weak.
Good proton donor. Poor proton donor.

Question 6

What is a conjugate base?

Answer 6

The species formed /left when an acid has donated a proton

ACID -PROTON = CONJUGATE BASE

Question 7

A strong acid forms a conjugate base. Is the conjugate base formed strong or weak?

Answer 7

Weak
Strong acids form week conjugate bases
Reason: The conjugate base which forms as little tendency to gain a H+ ion /Proton
Strong acids tend to remain dissociated

Question 8

The titration of sodium carbonate against HCL solution. Name the indicator used and the colour change at the end.
Why did you use this indicator?
How much indication was added and why?

Answer 8

Methyl orange.
Orange -> pink
Reason : titrating strong acid and strong base
2-3 drops. Indicator is a weak acid or weak base. If too much indicator was added, it would take part in the reaction.

Question 9

If HX represents a weak acid, write the conjugate base that forms . Would you expect this conjugate base to be weak or strong?

Answer 9

X-
Strong.
Weak acids tend to remain undissociated. The conjugate base i.e. X- has a strong tendency to accept a proton and form the undissociated acid again

Question 10

Explain the term dibasic

Answer 10

Donuts 2 protons / H+ ions per molecule e.g. H2SO4