On Target? Do this on your
Warm Up worksheet!
PLEASE put today’s date (2/22/16) in your Monday
warm-up square!
REVIEW: Why do some substances dissolve in water
while others don’t? Explain in complete sentences!
Why do some substances dissolve in
water while others don’t?
• What does salt have to have in order to
dissolve in water?
• CHARGES!
• What doesn’t dissolve in water?
• OIL!
• So what do we know about oil, based on this
information?
• Oil doesn’t have charges!
For today
1. Warmup
2. Review!
3. Big ideas!
• Objective: I can explain how charges
influence the properties of our substances
with both words and pictures.
Review From Properties Lab!
• Groups of chemical compounds share
macroscopic similarities
– Many hard, crystalline solids with high melting
points do not conduct electricity as solids, but do
conduct electricity when dissolved in deionized
water
– Medium-hard, powdery substances with low
melting points sometimes dissolve in water
partially, but conduct electricity poorly, if they do
at all
• What is causing this on the microscopic level?
Electricity is involved (Charges)!
Review from Electroscopes Lab:
• How do charged objects (plastic knife, glass
rod, balloon) react with the tiny paper bits?
• Did all of them move toward the balloon?
• What does this tell you about the charge of
the paper
Static Electricity
• Opposites attract!
• Like charges repel, and opposite charges
attract
• Does it matter which object is positive and
which one is negative?
– No!
A microscopic view of a stream of water falling past
a charged plastic knife and a charged piece of glass.
Solubility Review!
• “Like dissolves like”
• Water will dissolve other things with charges!
• So if you mix 2 things without charges, are
they soluble with each other?
– YES!
Salt Dissolves in Water
• How does salt dissolve in water?
• HINT: What is the formula for salt?
• What ions does it have? Na+Cl-
Why would salt conduct electricity in
water but NOT as a solid?
• Diamond white boarding!
• Think about:
1. What might be different about salt as a solid
crystal vs in a liquid?
2. What is salt able to do in water?
3. It can move around in water!
How can one substance dissolve in water and
NOT conduct electricity (sugar) while another
dissolves and DOES conduct electricity (salt)?
• Think about:
1. How does the conductivity meter work? Does
it have charge?
2. How might particles be charged differently?
3. What needs to happen for electricity to be
conducted?
4. Why would deionized water not conduct
electricity?
How salt dissolves
How sugar dissolves
Big Ideas!
• In your notebook, fill in the following
sentences:
1. Charges are important because__________.
2. Water is attracted to both positive and
negative objects because______________.
3. Water can dissolve objects with charges
by____________.
4. Salt can conduct electricity in water
because_________. Sugar cannot conduct
electricity in water because__________.