Definition of pH
State the definition for pH
Give the pH for a solution when given the molarity and access to a calculaltor
Write the equation for the process of dissolving a base in water
Give numbers and identities for ions formed when acids and bases dissolve in water
Explain what an is meant by an aqueous solution
Classify a substance as an acid or base by examination of the formulas
Fundamental ideas
The acid potential for an aqueous solution is indicated by the pH.
The pH scale is exponential. A change of pH by "1" unit reflects a ten-fold concentration change.
The pH scale is connected to the concentration of hydronium ions. The pH is low for solutions rich in hydronium ions. Temperature influences pH. Water solutions at 25oC are acidic when the pH is lower than 7.
Solutions at 25oC are considered neutral when the pH equals 7.
Definitions
sodium chloride
The hydrogen ion, H+ , does not exist in water. The lone pairs of electrons on the oxygen of the water molecule are attracted to the hydrogen ion, H+.
Hydrogen chloride hydronium ion chloride ion
HCl(g) + H-O-H --ý H3O+ (aq) + Cl-(aq)
In water the hydronium ion is the active agent formed by acids.
Substances will be acidic if a hydrogen atom has a weak bond to a nonmetal atom. Typically this means the hydrogen will be bonded to one of the halogens, oxygen, or sulfur.
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Nitric acid |
potassium hydroxide |
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water |
potassium nitrate |
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HNO3(aq) |
+ KOH(aq) |
---ý |
H2O(l) |
+ KNO3(aq) |
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Fundamental ideas
Bases are a source of OH1-
Potassium hydroxide potassium ions
KOH(s) + H2O(l) -----ý K1+ (aq) + OH1- (aq)
Some substances react with water to form hydroxide ions.
NH3 (s) + H2O(l) -----ý NH41+ (aq) + OH1- (aq)
Exercise:
Label the following as an acid or a base. When dissolved in water,. Click on formula to see answers. Give the formulas for the ions formed by each substance in aqueous solution.
Al(OH)3(s) HBr(g) Ca(OH)2(s) Fe(OH)3 (s)
Answer.
Al(OH)3(s) aluminum hydroxide dissolves in water and acts a base
Al(OH)3(s) + H2O(l) -----ý Al3+ (aq) + 3 OH1- (aq)
HBr(g) dissolves in water to form and acts as an acid.
HBr(g) + H-O-H --ý H3O+ (aq) + Br-(aq)
Ca(OH)2(s) calcium hydroxide dissolves in water and acts a base
Ca(OH)2(s) + H2O(l) -----ý Ca2+ (aq) + 2 OH1- (aq)
Fe(OH)3(s) ironIII hydroxide dissolves in water and acts a base
Fe(OH)3(s) + H2O(l) -----ý Fe3+ (aq) + 3 OH1- (aq)