Chemical Changes

Acidic (PH Scale)

• produce hydrogen ions (H⁺ ) in aqueous solutions

• PH less than 7

• car battery acid/vinegar/lemon juice

Alkaline

• release OH ions

• PH greater than 7

• Washing up liquid/bleach/drain cleaner

PH Scale

• 0 to 14

• measure of the acidity or alkalinity of a solution

Ways to measure PH

• chemical indicator

• PH probe (electronically)

PH probe is better because…

• Determining the colour of an indicator is subjective

• A probe produces a more accurate result high resolution as well

Indicator

• Dye that changes colour based on the PH of a solution

• universal indicator - made using multiple dyes and show a range of colours

Acid

A substance that forms an aqueous solution with a PH less than 7.

Base

A substance with a PH greater than 7

• substance that can neutralise an acid

Alkali

A base that dissolves in water to form a solution with a PH greater than 7

Neutralisation Reactions

acid + alkali -> salt + water

Ionic Equation for all neutralisation reaction (HAVE TO IDENTIFY NEUTRALIUSATION)

• H+ (aq) + OH- (aq) → H2O (l)

Neutralisation reaction definition

• reaction between acid and base in which H+ ions from the acid react with OH- ions from the base

Litmus Paper + Results

• alkali - blue

• acid - red

How to use indicator to measure the PH

• Add universal indicator solution (or dip universal indicator paper) into the solution.

• Observe the colour change.

• Compare the colour to a pH colour chart.

• Read off the pH value.

Strong acid

An acid that complete ionises / dissociates in an aqueous solution to release H+ ions

Weak Acid (carboxylic acids)

An acid that partially ionises / dissociates in an aqueous solution to release H+ ions

Acid strenght on reactivity

• strong acids higher reactivity

• the concentration of ions is higher

• the freuquency of collisons is higher

• increases rate of reaction

• opposite for weak acids

PH between strong and weak acids + reversibility?

• strong acid lower PH as it would fully ionise/dissassociate so release more H+ ions (not reversible)

• weak acid higher PH as it will partially ionise so release less H+ ions (reversible)

PH scale movement and H+ ions conc

• logarithimic scale

• If it moves up from PH 4 to PH 5 it divided by 10 in H+ ions conc
  If it moves down from PH3 to PH2 it is multiply by 10 in H+ ions conc

Strong acid examples

• HCL

• Nitric Acid HNO3

• Sulfuric Acid H2SO4