Transcript solutions conductivity

QOTD
• Why are electric eels so effective in saltwater?
SOLUTIONS
CONDUCTIVITY
MR. DUNNUM
ELECTROLYTES
oAre substances that form positive(+) and
negative (-) ions in water
oConduct an electric current
ELECTROLYTES IN THE BODY
oCarry messages sent to and from the
brain as electrical signals
oMaintain cellular function with the correct
concentrations electrolytes
CONDUCTION
ILLUSTRATED
Drop of CaCl2 (aq)
Resistor
330 Ω (ohms)
• Electric current : flow of charged particles.
• One type of current is electrons flowing
through a wire, from cathode (negative
electrode) to anode (positive electrode).
• Another type of current: anions and
cations moving through a solution
Cations move to the cathode, anions
move to the anode.
• External source of potential (voltage) is
required in both cases!
LED
IS IT A STRONG ELECTROLYTE, A
WEAK ELECTROLYTE, OR A
NONELECTROLYTE?
• Strong electrolytes include:
• Strong acids (all acids begin with H)
•
Ex: HCl, HBr, HI, HNO3, H2SO4, HClO4)
– Strong bases (bases end in –OH (Hydroxide)
– (IA and IIA hydroxides)
– Ex: NaOH, Ca(OH)2, KOH, Ba(OH)2
– Soluble Salts (Most water-soluble ionic compounds)
Ex: metal – nonmetal (NaCl)
metal - polyatomic ion (Na2SO4 )
NONELECTROLYTES
Dissolve as molecules only
No ions are produced in water
Do not conduct an electric current
H2O
C6H12O6 (s)  C6H12O6 (aq)
glucose
WHICH ONE
WORKS
• Electrolytes
dissociate to
produce ions.
The more the electrolyte dissociates, the more ions it produces.
• Dissolving Polar Covalent Compounds
Some dissolve only as molecules
EX: Sucrose
Dissolves but does
not dissociate into
ions
Timberlake, Page 239
* Dissolving Ionic Solutes
QUESTIONS FOR ANALYSIS
1.
Some substances conduct electricity because of the
ions present. Those substances that do not dissociate
into ions do not conduct electricity.
Electrolytes=dissociate to produce ions
Non-Electrolytes do not have ions to dissociate
2. COULD ANY OF THESE SUBSTANCES CONDUCT
ELECTRICITY IN THE SOLID FORM? EXPLAIN
o None of the substances can conduct electricity in the
solid form .
o EX: Ionic compound. When a salt is in a molten state / dissolved in
water, the ions can move and carry the electric current.
o in SOLID STATE= the ions cannot move, so the current cannot
flow.
o METALS: metals have free electrons which allow them to conduct
electricity in both solid and molten state.
o EX: Copper,steel,water,plasma and most metals conduct electricity
in solid form
3. EXPLAIN SOME POSSIBLE REASONS FOR
A HIGH CONDUCTIVITY MEASUREMENT IN A
FRESHWATER SAMPLE FROM A LAKE,
STREAM OR POND.
High concentration of ions (unusual anions and cations)
Nutrients
(e.g., phosphorus, nitrogen, carbon, silicon,
calcium, potassium, magnesium, sulfur,
sodium, chloride, iron) are primarily
transported to ponds and lakes via
streamflow, surface runoff and groundwater,
CONCLUSION
An electrolyte is a compound that, in aqueous solution,
conducts electricity. As liquids: salts, bases. When aq:
salts, acids, bases. When ions are present it can conduct
electricity.
ex> HCl(aq):
H+(aq) + Cl –(aq)
NaOH(aq): Na+(aq) + OH–(aq)
CuSO4(aq): Cu2+(aq) + SO42–(aq)
Nonelectrolytes do not conduct electricity. They do not ionize
and therefore have no moveable ions.
Acid: a compound that ionizes in water to form hydrogen
ions.
Base: an ionic hydroxide that dissociates in water to produce
hydroxide ions
A strong electrolyte has a greater percentage ionization
(most molecules are converted to ions).. Weak have a few
ions and more molecules so they conduct electricity at a
lesser percentage.