M2 ,, Acids

Question 1

Acid?

Answer 1

An acid releases H+ ions in aqueous solution

The most common strong acids are :
Hydrochloric ( HCl), sulfuric (H2SO4) and nitric (HNO3) acid; Ethanoic acid CH3COOH is a weak acid

Question 2

Bases?

Answer 2

Bases neutralise acids. Common bases are metal oxides, metal hydroxides and ammonia

A base readily accepts H+ ions from an acid: eg OH- ions accepts an H+ ion forming H2O
NH3 accepts an H+ ion forming NH4+ ion

Question 3

Alkalis?

Answer 3

An Alkali is a soluble base that releases OH- ions in aqueous solution;
The most common alkalis are sodium hydroxide (NaOH), potassium hydroxide (KOH) and aqueous ammonia (NH3)

Question 4

Strong acids?

Answer 4

Strong acids completely dissociate when dissolved in water

Question 5

Weak acids?

Answer 5

Weak acids only slightly dissociate when dissolved in water, giving an equilibrium mixture

Question 6

Neutralisation reactions?

Answer 6

ACID + BASE —> SALT + WATER

Acid + Carbonate —> Salt + Water + Carbon Dioxide
- Observations : In carbonate reactions there will be Effervescence due to the CO2 gas evolved and the solid carbonate will dissolve

Question 7

Why do Neutralisation reaction form salts?

Answer 7

A Salt is formed when the H+ ion of an acid is replaced by a metal ion or an ammonium ion

Question 8

Titration method?

Answer 8

•rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water)
•pipette 25 cm3 of alkali into conical flask
•touch surface of alkali with pipette ( to ensure correct amount is added)
•adds acid solution from burette
•make sure the jet space in the burette is filled with acid
•add a few drops of indicator and refer to colour change at end point
•phenolphthalein [pink (alkali) to colourless (acid): end point pink colour just disappears] [use if NaOH is used]
•methyl orange [yellow (alkali) to red (acid): end point orange]
[use if HCl is used]
•use a white tile underneath the flask to help observe the colour
change
•add acid to alkali whilst swirling the mixture and add acid dropwise at end point
•note burette reading before and after addition of acid •repeats titration until at least 2 concordant results are obtained- two readings within 0.1 of each other

Question 9

Recording titration results?

Answer 9

•Results should be clearly recorded in a table
•Result should be recorded in full (i.e. both initial and final readings)
•Record titre volumes to 2dp (0.05 cm3)

Question 10

Titration safety precautions?

Answer 10

Eye protection and gloves