Acid/Base Chemistry Science 10

Water – another view Normally we consider water as a covlent compound with the following formula: Normally we consider water as a covlent compound with the following formula: However, it is also possible to consider water as an ionic compound with the following formula: However, it is also possible to consider water as an ionic compound with the following formula: H2OH2O H + OH -

Water – in balance In a sample of pure water, some of the water molecules will dissociate into hydrogen ions (H + ) and hydroxide ions (OH - ) In a sample of pure water, some of the water molecules will dissociate into hydrogen ions (H + ) and hydroxide ions (OH - ) If the hydrogen ions and hydroxide ions are balanced, as they would be in pure water, the solution is neutral meaning that it is neither an acid or a base If the hydrogen ions and hydroxide ions are balanced, as they would be in pure water, the solution is neutral meaning that it is neither an acid or a base

Acids Acids are compounds that result in an increase in the hydrogen ions in a solution Acids are compounds that result in an increase in the hydrogen ions in a solution Normally these compounds will be the result of a hydrogen atom bonded with a non-metal or polyatomic ions and then dissolved in water. Normally these compounds will be the result of a hydrogen atom bonded with a non-metal or polyatomic ions and then dissolved in water. For example: For example: –Hydrochloric acid – HCl –Sulphuric acid – H 2 SO 4

Bases Bases are compounds that result in an increase in the hydroxide ion concentration in a solution Bases are compounds that result in an increase in the hydroxide ion concentration in a solution Normally these compounds will be the result of a metal combined with a hydroxide ion Normally these compounds will be the result of a metal combined with a hydroxide ion For example: For example: –Sodium hydroxide – NaOH –Calcium hydroxide – Ca(OH) 2

Neutralization Reactions When an acid and a base react, they combine to form water and a salt (not necessarily NaCl) When an acid and a base react, they combine to form water and a salt (not necessarily NaCl) For example: For example: –HCl + NaOH  NaCl + H 2 O –H 2 SO 4 + 2KOH  K 2 SO 4 + 2H 2 O –2H 3 PO 4 + 3Ca(OH) 2  Ca 3 (PO 4 ) 2 + 6H 2 O

Indicators Indicators are used to determine whether a compound is an acid or a base. Some common indicators are: Indicators are used to determine whether a compound is an acid or a base. Some common indicators are: –Litmus – red in acid, blue in base –Phenolphthalein – clear/white in acid, pink in base –Bromothymol Blue – yellow in acid, blue in base

pH Scale The pH scale is used to describe not only if a compound is an acid or base but also the strength of the acid or base The pH scale is used to describe not only if a compound is an acid or base but also the strength of the acid or base The scale runs from 0 to 14 with 0 being a strong acid, 14 being a strong base and 7 being neutral The scale runs from 0 to 14 with 0 being a strong acid, 14 being a strong base and 7 being neutral The pH scale is logarithmic which means that a change of one unit means a 10x change in strength and two units means a 100x change The pH scale is logarithmic which means that a change of one unit means a 10x change in strength and two units means a 100x change

Problems Page 218 Page 218 –2-4 Page 225 Page 225 –1-3 Page 236 Page 236 –2-4