Chapter 8 Changes in Matter
Lesson 3 Salts
Main Idea:
Salts are compounds made of metallic and nonmetallic elements. A salt may be
formed by an acid reacting to a base.
Vocabulary
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Salt (436) – a compound made of metal and nonmetal elements
Acid (438) – a substance that tastes sour and turns litmus paper red
Indicator (438) – changes color in a way to help you identify a substance
Base (439) – a substance that tastes bitter and turns litmus paper green
Neutralization reaction (439) – bases reacting with acids to form salts and water
Acidity (440) – strength of an acidic solution
Alkalinity (440) – strength of a basic solution
pH scale (440) – measures the amount of charged hydrogen particles
Deicers (443) – salt that dissolve into the ice and lowers its freezing point.
What is a salt?
Main Idea
Salts are compounds with high melting points, are hard and brittle, and conduct
electricity when dissolved.
Supporting Details
 A compound made from a metal and a nonmetal is often called a salt.
 The metals in the 1st 2 columns of the periodic table often combine with the
nonmetals in the 17th column of the table (2nd one from the right side) to form
salt.
 Salt and water are formed after one combines a strong acid with a strong base
 Properties of salt
o Particles of salt strongly attract each other in an orderly arrangement.
o Salts are hard and brittle.
o Salts have high melting points.
o A dissolved salt solution conducts electricity well.
 The metals and nonmetals in salts are electrically charged.
 If salt does not dissolve well in water, the solution will not be a good
conductor of electricity.
What are acids and bases?
Main Idea
Acids are substances that taste sour. Base are those substances that are bitter.
Never taste a substance to see if it is an acid or base. The substance could be toxic
or do something to burn the skin.
Supporting Details
 Acids
Acids are substances with a sour taste.
Acids often are a combination of hydrogen (H) and other nonmetal elements.
 Chemical formulas for acids usually begin with H.
o When acids dissolve in water, their molecules separate into charged particles
enabling an acid solution to conduct electricity.
o Acids can be used to form salts.
 The other reactant needs to supply the 2nd element for a salt to form.
Base
o Bases are substances with a bitter taste.
o Bases feel slippery, much like soap.
o Bases contain a metal atom joined with negatively charged particle called
hydroxide.
 Hydroxide is an atom of oxygen tightly stuck to an atom of hydrogen.
 Chemical formula for hydroxide is OH-.
o When bases dissolve in water, their particles separate into charged particles.
 The solution can conduct electricity like acid or salt solutions.
Bases react chemically with acids.
o The resulting products are salt and water.
o The reaction is called neutralization reaction.
 Acids change to water.
 Bases change to salt.
 The base supplies the metal element.
 The acid supplies the nonmetal element.
 The above elements rearrange themselves to form a salt.
 Antacids use a mild base to neutralize the acids in the stomach.
NEVER TASTE UNFAMILIAR SUBSTANCES TO SEE IF THEY ARE AN ACID OR
BASE.
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Are all acids and bases equally strong?
Main Idea
Acids and bases can have different strengths. The pH scale is used to determine
the strength or weakness of an acid or a base.
Supporting Details
 There are strong acids and bases and weak acids and bases.
o Acids
 Molecules of strong acids in solutions separate into charged particles
almost completely
 Molecules of weak acids in solutions separate only partially into charged
particles.
 Strong acids produce a large number of charged hydrogen particles;
weaker acids produce a smaller number of charged hydrogen particles.
o Bases
 The above comments apply to bases, except the strength of bases comes
from the number of charged hydroxide (OH-), not charged hydrogen (H-).
 Measuring the strength or weakness of acids and bases
o Acidity is the strength of an acid solution.
o Alkalinity is the strength of a base solution.
o A pH scale measures the acidity or alkalinity of a solution based on the
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amount of charged hydrogen particles in the solution.
 The scale runs from 0 (high acidity) to 14 (high alkalinity)
 A reading of 0 is the most acidic and the least basic.
 A reading of 14 is the most basic and the least acidic.
 A reading of 7 is neutral pH. Water is 0.
 Litmus paper is commonly used to measure acidity and alkalinity.
 The paper turns red when in contact with an acid.
 The paper turns blue when in contact with a basic.
Being able to measure acidity and alkalinity is important in farming,
environmental, and industrial activities.
How do we use salt?
Main Idea
Salt has been used for thousands of years. Its primary use was to remove water
from once-living things to preserve them. It was also used to add flavor to food
and to dissolve ice and snow.
Supporting Details
 Salt is used to remove water from once-living things to preserve them.
o Salt was used to preserve food when refrigeration was not available.
 Salt removes the water from the food.
 Bacteria can not survive in a dry environment. Dry food does not spoil as
quickly.
o Ancient Egyptians used salt to preserve the bodies of dead kings as
mummies.
 Salt is used to season food to give them more flavor.
o Table salt is sodium chloride.
 Different compounds are added to the salt to prevent it from clumping
when wet. They absorb the water that could cake the salt.
 Small amount of iodine is added to iodized salt to help prevent goiters, a
disease of the thyroid.
o Fine restaurants prefer sea salt as it contains different salts which provide a
richer flavor to the food.
 Salt is used as a deicer in colder regions to melt the snow and ice on roads and
walkways.
o Dissolving salt in ice lowers the freezing temperature of the solution.
 The snow and ice melt into slush.
o The salt also helps prevent slipping on pavements and skidding on roadways.
Where is salt found?
Main Idea
Salt occurs naturally. It can be found underground and in seawater.
Supporting Details
 Salt was formed early in the Earth’s history as a solid.
 Much of the salt is dissolved by rain and flows into the ocean.
 Salt is extracted from ocean water in shallow ponds.
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o The water is evaporated by the sun leaving solid crystals of salt.
o The crystals are collected, refined, and packed for use.
Salt is mined from underground deposits.