CHEM - Acid, Alkali and Titration
Chemistry, acid, alkali, titration - IGCSE | IBDP | DSE | GCE | AP Chemistry
When acids dissolve in water, they produce protons (H+ ions). These protons make the solution acidic.
HCl(aq) → H+(aq) + Cl-(aq)
H2SO4(aq) → 2H+(aq) + SO42-(aq)
When alkalis dissolve in water, they produce hydroxide ions (OH-). These hydroxide ions make the solution alkaline.
NaOH(aq) → Na+(aq) + OH-(aq)
Ca(OH)2(aq) → Ca2+(aq) + 2OH-(aq)
Tests for Acids and Alkalis
- Litmus indicator solution turns red in acidic solutions, and turns blue in alkaline solutions.
- Litmus papers are also used.
Phenolphthalein and Methyl Orange
Universal Indicator and pH scale
pH scale (0 to 14) shows the strength of acidic or alkaline solutions and can be measured by a universal indicator.
Neutralization reaction between an acid and an alkali produces a salt and water.
Acid + Base → Salt + Water
This is because hydrogen ion from the acid and hydroxide ion from alkali react to form water.
H+(aq) + OH-(aq) → H2O (l)
Example of neutralization reaction:
H2SO4(aq) + 2KOH(aq) → K2SO4(aq) + 2H2O(l)
HCl(aq) + NaOH (aq) → NaCl(aq) + H2O(l)
Titration is a method where a solution of known concentration is used to determine the concentration of another solution. The solution is added slowly to another solution until neutralization happens.
A student carries out a titration to find the concentration of some dilute sulfuric acid. She is given
She uses this method to do the titration.
After several repeats, the student calculated the average volume of phosphoric acid added to be 28.30 cm3.
(a) Find the balanced chemical equation for the neutralization reaction.
3NaOH + H3PO4 → Na3PO4 + 3H2O
(b) Calculate the amount, in moles, of NaOH in 25.0 cm3 of the sodium hydroxide solution.
0.180 x 25.0 / 1000 = 0.00450 moles
(c) Calculate the amount, in moles, of H3PO4 in the phosphoric acid solution.
0.00450 / 3 = 0.00150 moles
(d) Calculate the concentration, in mol/dm3 , of the phosphoric acid.
0.00150 x 1000 / 28.30 = 0.0530 mol/dm3
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