UNIT IX Solution Chemistry Lesson #1

I NTRODUCTION Solution Chemistry is the study of chemical reactions that occur in solutions… Reactions in solutions are chemists’ favourite type of reactions…because of how easy and convenient they are. Compare to: Reactions in the gas phase are complicated  need special containers (air-tight) Solid reactions  very slow or do not occur at all

L ET ’ S REMEMBER SOME DEFINITIONS Solution: is a homogeneous mixture Solvent: the component in the solution that exists in the ___________ amount. Solute: the component in the solution that exists in the ___________ amount.

S OLUTIONS AND SOLUBILITY Saturated solution: Unsaturated solution: Solubility : max. amount of a solute dissolved in a given amount of solvent at a constant temperature.

Saturated Vs Unsaturated

S OLUTIONS AND CONDUCTIVITY Do all solutions conduct electricity? How do we know?

Requirements to conduct electricity Experiments tell us that you need… Electrical charge to be transferred in the solution in order to produce electricity. IONS carry electrical charge!

Requirements to conduct electricity IONS carry electrical charge! Therefore, Ionic compounds can conduct electricity NaCl (aq) NaCl(s) Can covalent compounds conduct electricity? CS 2(aq)

THE CONDUCTIVITY OF AQUEOUS SOLUTIONS A conducting solution contains ions; the greater the concentration of ions, _____________the conductivity. A compound made up of a METAL and NONMETAL is IONIC, and forms a conducting solution in water because it breaks into ________ A substance made up of a NONMETAL and a NONMETAL is COVALENT, and will NOT form a conducting solution in water because it stays as a molecular compound.

NaCl (Ionic) in water The "+" and "-" ions are now free to move around. The "+" ions would be attracted to a negative electrode and the "-" ions would be attracted to a positive electrode. In this way, the ionic solution conducts a current.

What else can conduct electricity?? ACIDS and BASES form conducting solutions in water. Why? Because they can break into ions! HCl(aq) NaOH(aq) HCl(s)

What else can conduct electricity?? ACIDS and BASES form conducting solutions in water. 1- Think of acids as any compounds that starts with H 2- Think of bases as any compounds that end with OH Exception; if a compound starts with Carbon and ends with OH. It is an alcohol, not a base and can’t conduct electricity. Ex: CH 3 OH (can’t conduct electricity)

What else can conduct electricity?? Metals in all phases can conduct electricity Examples: Na(l), Cu(aq), Na(s)

So what can’t conduct electricity?? 1) Non-metals 2) Covalent compounds (metal + non-metal) 3) Organic compounds(usually start with Carbon-C- and contain hydrogens) Ex: CH 3 OH, C 14 H 10 * CH 3 COOH (exception)- can conduct. 4) Solids !!!!!!!!!!! (except if they’re metals)

TO CONDUCT or NOT TO CONDUCT??? This is the question..... CONDUCTDOESN’T CONDUCT Metals non metals ionicsolid Acids(solutions)covalent Bases(solutions) * organic compounds * CH 3 COOH (exception)

T HINK ABOUT THIS For solutions to form, and to mix chemical compounds together when adding a solute to a solvent to make a solution…bonds need to break and new bonds need to form! So, we need to remember the intermolecular forces that hold molecules together….

Back to forces between molecules… Van der Waals Forces: THREE main types: A. DIPOLE-DIPOLE FORCES B. LONDON FORCES C. HYDROGEN BONDING All are caused by dipoles!

A. A. DIPOLE-DIPOLE FORCES Caused by dipoles Dipole: A temporary separation of charges, where more electrons are found on one side on the atom than the other side. Dipole-Dipole Forces: a permanent dipole results from atoms with different ELECTRONEGATIVITY!

D IPOLE -D IPOLE FORCES Ex: HCl H 2 O

London Forces: LONDON FORCES exist for everything!!! London forces’ strength increases as the # of electrons is increased. Ex: Does He or Xe have a stronger london forces bond? B. LONDON FORCES

C. HYDROGEN BONDING Hydrogen Bond: strong dipole – dipole attraction between molecules containing a H – N, H – O, or H – F bond (because N,F and O are highly electronegative) *intermolecular bond (between molecules) *strongest van der Waals bonds – but still weaker than covalent and ionic

C. HYDROGEN BONDING Hydrogen Bond: strong dipole – dipole attraction between molecules containing a H – N, H – O, or H – F Ex: NH 3 and NH 3 H 2 O and H 2 O Hint: Look for HF or any molecule having OH or NH in its formula

C OMPARING STRENGTHS OF BONDS IONIC BOND  DIPOLE – DIPOLE ~ LONDON FORCE Intramolecular Intermolecular Ionic bonds will always be stronger than any intermolecular bond. Remember, London forces strength increases with the increased number of electrons.

E XPLAIN THIS : Boiling temperatures: ICl = 97 C (70 electrons) Br 2 = 59 C (70 electrons)

H OMEWORK Page 198,199 Questions 6,7 Question 8 (do a,c,e, etc) Question 9 Page 202, 203, 204 Question 11 and Question 12 Question 14 and Question 16