Reactions of acids - chemistry

What happens to acids and alkalis when dissolved in water? (in aqueous solution)

Acids break down and release H+ ions

Alkalis break down and release OH- ions

What is a concentrated acid?

an acid with a lot of acid and little water per set volume

What is a dilute acid?

An acid with a lot of water and little acid per unit volume

What is a strong acid?

An acid that ionises completely in water and fully breakdowns into it’s ions

The greater the number of H+ ions released, the stronger the acid

Examples of strong acids

Hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid

What is a weak acid?

An acid that only partially ionises in water

Examples of weak acids

Carboxylic acids such as ethanoic acid

Hydrochloric acid

HCl (aq)

Nitric acid

HNO3 (aq)

Sulfuric acid

H2SO4 (aq)

Phosphoric acid

H3PO4 (aq)

What is pH?

A logarithmic scale based on the concentration of H+ (aq) ions

Table of concentration of H+ (aq) ions in mol/dm³ and pH value

1.0 × 10^-1 = 1.0

1.0 × 10^-2 = 2.0

1.0 × 10^-3 = 3.0

1.0 × 10^-4 = 4.0

What happens to the pH when the acid is stronger?

There are more H+ (aq) ions in the solution so there is a lower pH

Describe colours of solution in relation to their pH when universal indicator is added

0 - red, 1 - dark orange, 2 - orange, 3 - yellow, 4-8 green, 9 - turquoise, 10 - pale blue, 11-12 dark blue, 13-14 purple

Colours for methyl red indicator

In acid = red, in alkali = yellow

Colours for phenolphthalein indicator

in acid = colourless, in alkali = pink

Acid + metal →

Salt + hydrogen

Acid + metal oxide →

salt + water

acid + alkali (metal hydroxide) →

salt + water

acid + metal carbonate →

salt + water + carbon dioxide

ammonia + acid →

ammonium acid

hydrochloric acid →

… chloride salts

Nitric acid →

… nitrate salts

Sulfuric acid →

… sulphate salts

Neutralisation reaction

acid + base → salt + water

Ionic equation for a neutralisation reaction between an acid and an alkali

H+(aq) + OH-(aq) → H20(l)

What indicators should you use for titration and why?

Indicators that only have one colour change (NOT universal indicator)

What is the end-point?

The pH at which the indicator changes colour

Soluble meaning

Able to dissolve in water

Saturated meaning

high concentrated of solute dissolved in solvent

Concordant results

results that are within 0.10 cm³ of each other

ammonium ion

NH4+

nitrate ion

NO3-

hydroxide ion

OH-

sulphate ion

SO4 2-

carbonate ion

CO3 2-

Describe method to make pure, dry crystals of copper sulphate from a metal oxide and a dilute acid

Add sulfuric acid to a beaker and gently warm it over a Bunsen burner. Turn off heat and add in copper oxide one spatula at a time while stirring continuously. Continue to copper oxide is in excess and residue is left behind. Filter the solution through a funnel and filter paper into a conical flask. Transfer the filtrate to an evaporating basin and gently heat over boiling water over Bunsen burner to evaporate some water off. Once crystals start to form, remove basin and leave to crystallise. Once crystals have formed, dry them off with filter paper to produce dry crystals of copper sulphate.

Describe how to do a titration to find the exact volume of sulfuric acid needed to neutralise 25cm3 of sodium hydroxide solution

Rinse pipette with distilled water and sodium hydroxide. Rinse burette with distilled water and sulfuric acid. Measure 25cm3 of sodium hydroxide into pipette then transfer to conical flask. Add 3 drops of methyl orange/phenolphthalein. Fill burette with sulfuric acid so meniscus is exactly at zero. Slowly drop acid into conical flask while swirling until indicator changes colour. Record the final volume of acid. Washout out conical flask with distilled water and repeat titration until two readings agree to within 0.10 cm3 (concordant results)