Acids and Alkalis

• The pH scale is used to measure the acidity or alkalinity of solutions.
• The Ph scale is a number scale from 0-14
• An aqueous solution is formed when a solid substance is dissolved to form a liquid
• A neutral solution has a ph value of 7
• Alkaline substances have a ph value above 7
• Acidic substances have a ph value below 7
• Hydrochloric acid has a pH of 0-1
• • Hydrochloric acid pH = 0-1
  • Stomach pH = 1
  • Lemons pH = 2
  • Vinegar pH = 3
  • Apple pH = 3-4
  • Tomatoes pH = 4
  • Bananas pH = 5
  • Milk pH = 6
  • Pure water pH = 7
  • Blood pH = 8
  • soaps pH = 8-10
  • Amonious solution pH = 11
  • Bleach pH = 12
  • Drain cleaner pH = 13
  • Sodium Hydroxide pH = 13-14
• The pH of a substance can be tested only if it as aqueous solution, if that is not the case the substance must be dissolved in water (a solvent)
• Tests can be done using an indicator or a pH meter
• Indicators

  • An indictor is a substance which will change color depending on the solution it is mixed with.
  • some are in liquid form, e.g : universal indicator.
  • others are strips of paper, e.g : Litmus paper
• pH meter

  • a numerical value of the pH is given straight to us. As long as the pH meter has been preserved well the measurement should be accurate meaning the measurement is close to the true value.
• • Litmus paper will be red in acidic solutions and blue in alkaline solutions
  • universal indicator changes color at many different pH value.
• • acids form acidic solutions in water
  • acids are sources of hydrogen ions ,H+
  • a substance is acidic because of the presence of hydrogen, any acid will produce hydrogen ions.
• Some acids:

  • Hydrochloric acid (aqueous) > HCL
  • sulphuric acid (aqueous)> H2SO4
  • citric acid > C2H5COOH
  • phosphorus acid H2PO4
  • Nitric acid > HNO3

  all acids give hydrogen ions when reacting
• the number of hydrogen ions determines how acidic the substance is.

  • H+ > = less acidic *if the hydrogen is on the higher side it is less acidic*
  • H+ < = more acidic *if the hydrogen is in the lower range it is more acidic*
• • alkalis form alkaline solutions in water
  • alkalis are sources of hydroxide ions, OH-
  • for example, sodium hydroxide produces hydroxide ions
• alkalis example:

  sodium hydroxide

  • NaOH (aqueous) -> Na+ (aq.) + OH- (aq.)

  all alkalis give hydroxide ions when reacting
• neutral substances do not produce anything

  • neutral substances are formed from reaction of acid and alkali
  • examples of neutral substances; pure water and table salt
• More indicators

  • Methyl orange; in acidic substances it turns red in neutral its yellow and in alkaline its yellow as well
  • Phenolphthalein; in acidic substances it is colorless as well as neutral substances, but in alkaline it turns pink.
• Corrosive means that it can cause damage to another substance and cause certain damage or burns.

  Most acids are corrosive.
• neutralization reactions

  • A chemical reaction happens if you mix together an acid and a base.
  • the reaction is neutralization. A neutral solution is made if you add just the amount of acid and base together.
  • a base is basically an alkali
• naming the salt

  • salt have scientific names. For example, the scientific name of table salt is sodium chloride.
  • names of salts can be worked out from the name of the acid and the alkali that reacts to make them.
  • there are two parents to a salts name:

  first word: metal taken from alkali

  second word: usually ends in <ide> or <ate>

  formula for forming a salt:

  • acid + base -> salt + water
  • e.g: hydrochloric acid + sodium hydroxide -> sodium chloride
• e.g:

  • nitric acid + sodium hydroxide -> sodium nitrate (+water)

  imagine nitric cid marries sodium hydroxide, sodium will keep her first name but he surname now becomes nitrate.

  nitric -> nitrate

  hydrochloric -> chloride

  sulphuric -> sulphate
• reactions of acids

  1. reactions with metals; acid + metal -> salt + water
  2. reactions with bases; acid + base -> salt + water
  3. reactions with carbonates; acid + carbonate -> salt + carbon dioxide + water