Acids, Bases and Salts

All acids ____ when dissolved in water

dissociate to produce H+ ions

All alkalis___when dissolved in water

dissociate to produce OH- ions

why is universal indicator not used in titration

gradual colour change, can’t see exact point it neutralises

Methyl orange - colour in acidic solution + alkaline solution

• acidic = red

• alkaline = yellow

litmus - colour in acidic solution + alkaline solution

• acidic = red

• alkaline = blue

Phenolphthalein - colour in acidic solution + alkaline solution

• acidic = colourless

• alkaline = pink

What Ph values are acidic?

6→0

neutral PH

7

what PH values are alkaline

8→14

what is a strong acid?

A strong acid dissociates 100% when added to water

what is a weak acid?

only partially dissociates therefore far fewer H+ ions

definition/ characteristics of an Acid

• dissociate in water to produce H+ ions

• PH value below 7

• An acid is a proton donor

Definition of a base

• neutralise acids to form salt

• proton acceptors

Alkali definition

• soluble bases

• produce OH- ions in water

• PH value greater than 7

Acid + base →

salt + water

Acid + metal →

salt + hydrogen

Acid + carbonate →

salt + water + carbon dioxide

Acid + Ammonia →

ammonia salt

What are the 2 methods of making salts when the salt is soluble?

1. titration (uses 2 solutions)

2. Adding solid base to acid (aq + s)

how to do a titration to obtain a salt

PART 1

• pipette 25cm³ of solution 1(named in exam) into a conical flask + indicator

• fill burette with 2nd solution - note starting vol

• add 1 to 2, swirling

• stop when 1 drop changes colour

• note volume added - repeats, mean

• do again without indicator adding volume calculated

PART 2

• heat in evaporating basin to get SOME of the water

• allow to cool, so crystals form

• filter to obtain crystals

• dab between paper towels

how to get salt through solid base + acid

PART 1

• add solid base to acid

• stop when solid base no longer reacts (excess)

• filter to remove excess base

PART 2 (same as titration)

• heat in evaporating basin to get SOME of the water

• allow to cool, so crystals form

• filter to obtain crystals

• dab between paper towels

how to obtain salt when salt is insoluble?

precipitation (aq + aq → s + aq)

how to do precipitaton

• mix 2 solutions that contain ions of insoluble salt

• e.g Metal ion needed (NO₃) _aq

  • (group 1) non metal ion needed

• filter to get insoluble salt

• wash with distilled water

• dab to dry

group 1 solubility

ALL soluble

nitrates solubility

soluble

chlorides solubility

soluble except AgCl and PbCl₂

sulfates solubility

soluble except BaSO₄, CaSO₄ and PbSO₄

carbonates solubility

insoluble, except

• sodium carbonate

• potassium carbonate

• ammonium carbonate

hydroxides solubility

insoluble except

• sodium hydroxide

• potassium hydroxide

• calcium hydroxide(slightly soluble)

write a balanced symbol equation for the reaction between copper oxide and sulfuric acid

CuO(s) + H₂SO₄ (aq)→ CuSO₄ (aq)+ H₂O(l)

copper oxide/sulfuric acid practical

why was a measuring cylinder used to measure acid, not burette/pipette

you do not need a precise measurement of HCl - copper added in excess

copper oxide/sulfuric acid practical

why was the acid warmed?

to increase rate of reaction

copper oxide/sulfuric acid practical

why was acid not allowed to boil?

safety reasons - so it doesn’t get on skin

copper oxide/sulfuric acid practical

why was excess copper oxide used?

to ensure all the HCl is reacted/neutralised so the salt is pure

copper oxide/sulfuric acid practical

why is it important to remove excess copper oxide

to ensure we get pure CuSO₄ crystals

copper oxide/sulfuric acid practical

why did you leave the copper sulfate on the windowsill to crystallise, instead of just heating it to boil off all the water

Hydrated Copper sulfate crystals contain water. heating to dry would give anhydrous copper sulfate (white powder)

how to prepare a sample of pure, dry lead (II) sulfate

1. Add 75 cm3 of lead nitrate and 75 cm3 potassium sulfate to a beaker. Mix the solutions with a glass rod until a precipitate forms.

2. Put the filter paper in the funnel and place it over the conical flask.

3. Pour the mixture from the beaker into the funnel.

4. Use distilled water to wash any solid left in the beaker into the funnel. Wash the filtrate with distilled water. will remove traces of potassium nitrate.

5. Transfer the filtrate onto an evaporating dish and leave on windowsill

6. filter out crystals, dab between paper towels to dry

Universal indicator colour - acid/alkali

acid - red

alkali - purple

(scale)