AK: ACIDS AND ALKALIS

Acid definition

acid is a substance that dissociates in water to produce hydrogen ions

What do all acids contain?????

All acids contain H+ ions

PHYSICAL PROPERTIES of ACIDSSS

• Sour taste

• Turns damp blue litmus paper red

• pH smaller than 7

• Conducts electricity when dissolved in water

ALKALINE and BASES

• bases are metal oxides and metal hydroxides → oxide and hydroxide ions

• Alkaline is under base (base is the boss)

• Alkalis are bases that are soluble in water 

  • aqueous solution contains hydroxide ions 

  • Alkalis dissociate in water to form hydroxide ions

PHYSICAL PROPERTIES of ALKALINES

• Bitter taste

• Soapy touch

• Turns damp red litmus paper blue

• pH bigger than 7

• Conducts electricity when dissolved in water

pH SCALE:

• pH7 is neutral (water)

• pH lower than 7, higher acidity

• pH bigger than 7, higher alkalini

solution with smaller pH value has?

higher concentration of hydrogen ions present

solution with higher pH value has?

lower concentration of hydrogen ions present

IMPORTANCE OF pH:

• Different pH values in body

• Hair

  • Shampoo: alkaline (damage hair)

  • Conditioner: mildly acid (restore hair)

• Food preservation

  • Acid preserves food 

• Garden

  • Some plants grow better in acidic soil while others grow better in alkaline soil

INDICATORS

• Test for presence of acids or alkalis

• Can typically provide only approximate pH values

TYPES OF INDICATORS

1. Litmus paper

2. Common indicators 

3. Universal indicator (“rainbow” order)

4. Natural indicators

Litmus

1. CANNOT test for level of acidity or alkalinity 

2. Can be in solution form (liquid) or solid

Common indicators

1. Change colours 

Litmus

1. Acid: red 

2. Alkaline: blue

Phenolphthalein

1. Acid: colourless

2. Neutral: colourless

3. Alkaline: pink

Methyl orange

1. Acid: red

2. Neutral: yellow

3. Alkaline: yellow

Bromothymol blue

1. Acid: yellow

2. Neutral: green

3. Alkaline: blue

Universal indicator (“rainbow” order)

1. Strong acid: red 

2. Neutral solution: green

3. Strong Alkali: purple

Natural indicators

• Seldom used:

  • Waste effort to obtain them

  • Colour change is not standardised, will vary according to environment (Very ma fan)

1. Leaves, flowers, fruits

2. Contain chemicals/pigments that can change colour depending on whether its acidic or alkaline

pH METER

1. More specific and accurate