THE BIG IDEA
Acid + base → salt + water
For an acid and a metal hydroxide or metal oxide. A carbonate also produces carbon dioxide.
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01 / THE VIRTUAL LAB
Find the neutral point Reset experiment
Start with 25.00 cm3 of hydrochloric acid. Add sodium hydroxide and watch the pH change. Can you use up the acid without leaving excess alkali?
HCl concentration
0.050 mol/dm³ 0.100 mol/dm³ 0.200 mol/dm³
NaOH concentration
0.050 mol/dm³ 0.100 mol/dm³ 0.200 mol/dm³
NaOH added 0.00 cm³
Move the slider, or add a little at a time.
Add 1 cm³
Add 0.05 cm³
Show equivalence point
Acid is in excess. Add sodium hydroxide to begin neutralisation.
pH 1.00 Acidic
Liquid colour represents approximate universal indicator colour.
H+ remaining in excess 2.500 mmol
OH− remaining in excess 0.000 mmol
NaCl formed 0.000 mmol
See the chemistry & calculation
HCl(aq) + NaOH(aq) → NaCl(aq) + H2 O(l)
H+ (aq) + OH− (aq) → H2 O(l)
Na+ and Cl− are spectator ions: they stay dissolved. The salt has formed, but crystals need to be separated from the water.
n(HCl) = 0.100 × 25.00 / 1000 = 0.002500 mol. At equivalence, the same amount of NaOH is needed: 25.00 cm³.
Ideal strong acid–strong alkali model at 25 °C, assuming additive volumes and Kw = 10−14 . The pH includes water autoionisation. mmol means millimoles; 1 mmol = 0.001 mol. Excess ion amounts above exclude the small contribution from water.
02 / CHOOSE THE REACTANTS
Which salt will you make? The acid supplies the salt's negative ion. The base supplies its positive ion. Change either reactant to explore nine balanced reactions.
Choose an acidHydrochloric acid · HCl Nitric acid · HNO₃ Sulfuric acid · H₂SO₄
Choose a baseSodium hydroxide · NaOH Copper(II) oxide · CuO Copper(II) carbonate · CuCO₃
Chloride from HCl3 2 SO4
ACID + ALKALI
Sodium chloride
NaCl
HCl(aq) + NaOH(aq) → NaCl(aq) + H2 O(l)
Hydrochloric acid + sodium hydroxide → sodium chloride + water.
Both reactants are soluble. Use titration to find the reacting volumes; excess alkali cannot be removed by filtration.
See the titration method →
03 / FROM SOLUTION TO CRYSTALS
Match the graphics to the steps 8 steps · 8 marks
Match each graphic to the correct experiment step. Use every graphic once, then check your answers.
HCl
NaOH +
indicator
HCl
NaOH
No
indicator
Evaporate
Cool
Gentle heat
Dry salt crystals
Filter paper
CuO
Add small portions
Excess
solid
Some CuO remains
Solid
residue
Salt
solution
Concentrate
Blue crystals
1 Choose a step 2 Choose a graphic 3 Check your answers
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SOLUBLE ALKALI
Titrate, then crystallise
Example: sodium chloride from hydrochloric acid and sodium hydroxide.
Measure & titrate. Pipette a fixed volume of alkali. Add a suitable indicator, then add acid from a burette to the end point. Record the volume.
Repeat without indicator. Mix the measured reacting volumes again so indicator does not contaminate the salt.
Concentrate & cool. Gently evaporate some water, then leave the concentrated solution to cool and crystallise.
Collect & dry. Filter the crystals and dry them between filter papers.
INSOLUBLE OXIDE OR CARBONATE
Add excess, then filter
Example: copper(II) sulfate from dilute sulfuric acid and copper(II) oxide.
React with warm acid. Add small portions of the insoluble solid to gently warmed dilute acid and stir.
Add excess solid. Continue until some solid remains, showing the acid has been used up. A carbonate also releases CO2.
Filter the mixture. Remove unreacted solid. The salt solution passes through as the filtrate.
Concentrate, cool & collect. Evaporate some water, cool to form crystals, then filter and dry them.
Neutralisation does not mean every salt has pH 7. HCl and NaOH give a neutral solution at equivalence at 25 °C. Salts made from weak acids or weak bases can give acidic or alkaline solutions. Investigate salt solutions with litmus →
04 / CHECK YOUR UNDERSTANDING
Put the chemistry to work 6 questions / explanations included Choose an answer for each question, then check your understanding.