CHAPTER 7 – REACTIONS IN WATER SOLUTIONS Reactions in water solution involve dissolved ionic compounds and acids DISSOLVED IONIC COMPOUNDS When an ionic compound dissolves in water, the ions separate from each other 7A-1 (of 24) DISSOCIATION – The separation of ions from an ionic compound during the dissolving process

NaCl →Na + + Cl - (s)(aq) NaCl (s) NaCl (aq) 7A-2

MgBr 2 →Mg Br - (s)(aq) MgBr 2 (s) MgBr 2 (aq) 7A-3

Fe(NO 3 ) 3 → Fe NO 3 - (s)(aq) Fe(NO 3 ) 3 (s) Fe(NO 3 ) 3 (aq) 7A-4

STRONG ELECTROLYTE – A compound that dissolves in water and produces many ions Water soluble ionic compounds are strong electrolytes Electrolyte solutions conduct electricity because the dissolved ions are free to move throughout the solution Strong electrolyte solutions conduct electricity well 7A-5

PRECIPITATE – A solid formed when two solutions are mixed PRECIPITATION REACTIONS Dissolved ions that have a strong attraction for each other will precipitate out of a solution 7A-6

5 SOLUBILITY RULES FOR DISSOLVED IONS IN DILUTE SOLUTIONS 1 – Group I and NH 4 + ions never precipitate out of solution with anions 2 – NO 3 - and C 2 H 3 O 2 - ions never precipitate out of solution with cations 4 – SO 4 2- ions never precipitate out of solution with cations except with Hg 2 2+, Pb 2+, Ca 2+,Sr 2+, or Ba 2+ ions 3 – Cl -, Br -, and I - ions never precipitate out of solution with cations except with Ag +, Hg 2 2+, or Pb 2+ ions 5 – CO 3 2-, OH -, PO 4 3-, and S 2- ions do precipitate out of solution with cations except not with Group I and NH 4 + ions 7A-7

Determine if a precipitate will form if the following solutions are mixed: Mg(NO 3 ) 2 (aq) and KBr (aq) No NaI (aq) and Pb(C 2 H 3 O 2 ) 2 (aq) Yes – PbI 2 (see Rule 3) Li 2 SO 4 (aq) and CaCl 2 (aq) Yes – CaSO 4 (see Rule 4) (NH 4 ) 2 CO 3 (aq) and Ni(NO 3 ) 2 (aq) Yes – NiCO 3 (see Rule 5) 7A-10

If two ionic solutions are mixed, a pair of ions may combine to form a precipitate AgNO 3 (aq)KCl (aq) KNO 3 (aq) + AgCl (s) 7A-11

If two ionic solutions are mixed, a pair of ions may combine to form a precipitate AgNO 3 (aq)KCl (aq) KNO 3 (aq) + AgCl (s) 7A-12

AgNO 3 + KCl → AgCl + NaNO 3 (aq) (s)(aq) MOLECULAR EQUATION Ag + (aq) + NO 3 - (aq)+ K + (aq) + 2Cl - (aq) →AgCl (s) + K + (aq) + NO 3 - (aq) IONIC EQUATION Ag + (aq) + Cl - (aq) → AgCl (s) NET IONIC EQUATION 7A-13

Solutions of iron (II) chloride and sodium hydroxide are mixed FeCl 2 + NaOH → Fe(OH) 2 + NaCl22(aq) (s)(aq) Write in ionic form: Fe 2+ (aq) + 2Cl - (aq)+ 2Na + (aq) + 2OH - (aq) → Fe(OH) 2 (s)+ 2Na + (aq) + 2Cl - (aq) Write in net ionic form: Fe 2+ (aq) + 2OH - (aq) →Fe(OH) 2 (s) Write in molecular form: 7A-14

Solutions of potassium sulfate and barium nitrate are mixed K 2 SO 4 + Ba(NO 3 ) 2 → KNO 3 + BaSO 4 2(aq) (s) Write in ionic form: 2K + (aq) + SO 4 2- (aq)+ Ba 2+ (aq) + 2NO 3 - (aq) → + BaSO 4 (s)2K + (aq) + 2NO 3 - (aq) Write in net ionic form: SO 4 2- (aq) + Ba 2+ (aq) →BaSO 4 (s) Write in molecular form: 7A-15

Solutions of aluminum chloride and sodium carbonate are mixed Write in ionic form: Write in net ionic form: Write in molecular form: 7A-16

ACIDS When dissolved in water, acid molecules break apart into hydrogen ions and their corresponding anions IONIZATION – The formation of ions from a molecular compound during the dissolving process 7A-17

HCl →H + + Cl - (g)(aq) HCl (g) HCl (aq) (ionized form) 7A-18

STRONG ACID – An acid in which all of the molecules release hydrogen ions in water solution HCl, HBr, HI, and oxyacids with at least 2 more O’s than H’s Strong acids are strong electrolytes like soluble ionic compounds because their solutions contain many ions and conduct electricity well Strong acids are written in ionized form in ionic equations HNO 3 H 2 SO 4 HClO 4 H 2 CO 3 7A-19

Solutions of hydroiodic acid and barium hydroxide are mixed HI + Ba(OH) 2 → H(OH) + BaI 2 2(aq) (l)(aq) Write in ionic form: 2H + (aq) + 2I - (aq)+ Ba 2+ (aq) + 2OH - (aq) → 2H 2 O (l)+ Ba 2+ (aq) + 2I - (aq) Write in net ionic form: 2H + (aq) + 2OH - (aq) →2H 2 O (l) Write in molecular form: 2 H + (aq) + OH - (aq) → H 2 O (l) 7A-20

HF →HF (aq)(g) HF (g) HF (aq) (molecular form) 7A-21

WEAK ACID – An acid in which all of the molecules do not release hydrogen ions in water solution All acids except HCl, HBr, HI, and oxyacids with at least 2 more O’s than H’s Weak acids are written in molecular form in ionic equations Weak acids are weak electrolytes because their solutions contain small numbers of ions and barely conduct electricity Weak acids are written in molecular form in ionic equations 7A-22

Solutions of sulfurous acid and potassium hydroxide are mixed H 2 SO 3 + KOH → H(OH) + K 2 SO 3 2(aq) (l)(aq) Write in ionic form: H 2 SO 3 (aq)+ 2K + (aq) + 2OH - (aq) → 2H 2 O (l)+ 2K + (aq) + SO 3 2- (aq) Write in net ionic form: H 2 SO 3 (aq) + 2OH - (aq) →2H 2 O (l) + SO 3 2- (aq) Write in molecular form: 2 7A-23

Solid copper (II) oxide is added to a solution of hydrochloric acid CuO + HCl → CuCl 2 + H 2 O2(s)(aq) (l) Write in ionic form: CuO (s)+ 2H + (aq) + 2Cl - (aq) → + H 2 O (l)Cu 2+ (aq) + 2Cl - (aq) Write in net ionic form: CuO (s) + 2H + (aq) → Cu 2+ (aq) + 2H 2 O (l) Write in molecular form: 7A-24