ACIDS & BASES Last section!

Lesson Outline What are acids & bases? What are acids & bases? Properties of acids and bases Properties of acids and bases Formulas for acids and bases Formulas for acids and bases The pH scale The pH scale

What are Acids & Bases? Chemists use classification systems to make sense of matter Chemists use classification systems to make sense of matter Acids and bases are types of compounds that have characteristic formulas & similar chemical behaviours Acids and bases are types of compounds that have characteristic formulas & similar chemical behaviours E.g. lemon juice; baking soda E.g. lemon juice; baking soda

Properties of Acids Acids are sour-tasting, water-soluble substances Acids are sour-tasting, water-soluble substances They are very reactive and combine with many other substances They are very reactive and combine with many other substances (e.g. Mg (s) + 2 HCl (aq)  MgCl 2 + H 2(g) ) (e.g. Mg (s) + 2 HCl (aq)  MgCl 2 + H 2(g) ) Acids react with compounds containing carbonate and hydrogen carbonate groups Acids react with compounds containing carbonate and hydrogen carbonate groups (e.g. 2 HCl (aq) + CaCO 3(s)  CO 2(g) + H 2 O (l) + CaCl 2(aq) (e.g. 2 HCl (aq) + CaCO 3(s)  CO 2(g) + H 2 O (l) + CaCl 2(aq)

Properties of Acids Acids are good conductors of electricity (think of BATTERY ACID) because… Acids are good conductors of electricity (think of BATTERY ACID) because… When acids dissolve in water, they release hydrogen ions (H + ) When acids dissolve in water, they release hydrogen ions (H + ) HCl (aq)  H + (aq) + Cl - (aq) HCl (aq)  H + (aq) + Cl - (aq)

Properties of Bases Bases are bitter-tasting, water-soluble substances Bases are bitter-tasting, water-soluble substances They feel slippery in aqueous solutions They feel slippery in aqueous solutions Think of soap!! Think of soap!! Bases are good conductors of electricity because… Bases are good conductors of electricity because…

Properties of Bases When bases dissolve in water, they release hydroxide ions (OH - ) When bases dissolve in water, they release hydroxide ions (OH - ) E.g. NaOH (aq)  Na + (aq) + OH - (aq) E.g. NaOH (aq)  Na + (aq) + OH - (aq) Substances described as basic may also be described as alkaline Substances described as basic may also be described as alkaline What does this remind you of? What does this remind you of?

Formulas for Acids & Bases Acid formulas begin with a hydrogen Acid formulas begin with a hydrogen E.g. HCl, H 2 SO 4, H 3 PO 4 E.g. HCl, H 2 SO 4, H 3 PO 4 Base formulas are trickier…most contain the hydroxide ion (e.g. sodium hydroxide is NaOH) – some contain the bicarbonate or hydrogen carbonate group (e.g. sodium hydrogen bicarbonate is NaHCO 3 ) Base formulas are trickier…most contain the hydroxide ion (e.g. sodium hydroxide is NaOH) – some contain the bicarbonate or hydrogen carbonate group (e.g. sodium hydrogen bicarbonate is NaHCO 3 )

The pH Scale Chemists use the pH scale to represent how acidic or basic a solution is Chemists use the pH scale to represent how acidic or basic a solution is A very acidic solution has a very low pH value A very acidic solution has a very low pH value A very basic solution has a very high pH value A very basic solution has a very high pH value Water (neutral) has a pH of 7 Water (neutral) has a pH of 7

The pH Scale The pH scale is LOGARITHMIC The pH scale is LOGARITHMIC Means that a change of one unit on the scale represents a tenfold effect on the concentration of the solution Means that a change of one unit on the scale represents a tenfold effect on the concentration of the solution For example, a solution with pH of 3 is 10 times more acidic than a solution with a pH of 4 For example, a solution with pH of 3 is 10 times more acidic than a solution with a pH of 4 pH = -log 10 [H + ] “concentration of hydrogen ions in solution” pH = -log 10 [H + ] “concentration of hydrogen ions in solution”

[H + ]pHExample Acids 1 X HCl 1 x Stomach acid 1 x Lemon juice 1 x Vinegar 1 x Soda 1 x Rainwater 1 x Milk Neutral1 x Pure water Bases 1 x Egg whites 1 x Baking Soda 1 x Tums ® antacid 1 x Ammonia 1 x Mineral Lime - Ca(OH) 2 1 x Drano ® 1 x NaOH