Video Transcript
In this video, we will learn how to
distinguish between acids and bases and identify examples from everyday life.
In the first section of this video,
we will take a look at acids found in everyday life. Acids are frequently encountered in
sour-tasting foods and some drinks. Citrus fruits, such as lemons,
limes, and oranges, contain acids, and they taste sour. Vinegar can be used in cooking and
salads to sharpen the taste. Fizzy drinks, like soda and cola,
also contain acids, which are quite safe to drink.
Some acids are associated with more
dangerous items. The acid found inside a car battery
would not be consumed as it would cause great harm. The acid within a car battery would
be considered to be corrosive. A corrosive substance is one that
has high reactivity that causes damage upon contact with other materials. Corrosive acids are even found in
nature. Some ants can spray corrosive acid
to ward off predators. When working with corrosive
substances, such as corrosive acids, it is necessary to take the appropriate safety
precautions. Gloves and eye protection must be
worn.
Bases are also encountered in
everyday life. Soluble bases are found in drain
cleaners. A similar soluble base is found in
oven cleaner, where it is used to dissolve fatty deposits. Just like the dangerous acid in a
car battery, these cleaning products are also corrosive. So acids and bases alike can be
corrosive. It would be necessary to take the
same precautions when using these corrosive products as when using dangerous acidic
products. Wear eye protection and gloves. Other products containing bases
include toothpaste and antacids used to treat indigestion. These products are clearly not
corrosive and are safe to consume or place in contact with skin.
In the laboratory, it would clearly
not be safe to put substances into our mouth to see if they taste sour or not. We have a much better way of
testing to see if something is acidic or basic. An acidic solution can be tested
with litmus paper. The type of litmus paper we use for
this test must be blue litmus paper. When dipped into the acidic
solution, the indicator dye in the blue litmus paper will turn red. Basic solutions can be tested in a
similar way, but we must use red litmus paper instead. When red litmus paper is dipped
into a basic solution, it will turn blue. If a solution was tested with blue
litmus paper and it stayed blue and then it was tested with red litmus paper, which
stayed red, then we would have a neutral solution that is neither acidic nor
basic.
Let us now look at some of the
common acids found in the laboratory and their chemical composition. Three acids that are commonly
encountered in the laboratory are hydrochloric acid, sulfuric acid, and nitric
acid. The chemical formulas for these
acids are HCl, H2SO4, and HNO3. In hydrochloric acid, the -chloric
part of the name tells us that it contains chlorine atoms. The name for sulfuric acid gives us
a clue that the formula contains a sulfur atom. And nitric acid contains a nitrogen
atom in its formula.
Most notably though, the thing that
these formulas all have in common is that they contain hydrogen. In fact, this is an important
aspect of the definition for an acid. An acid is a substance that
dissociates in water, producing positive hydrogen ions. We can see how this process happens
using hydrochloric acid as an example. A hydrogen chloride molecule
contains one hydrogen atom and one chlorine atom bonded together. When it is placed into water, the
molecule dissociates. This means the bond breaks apart
and two oppositely charged ions are formed. One ion is a hydrogen ion with a
positive charge. The other ion is a chloride ion
with a negative charge. It is the hydrogen ions in the
solution that makes the solution acidic. So hydrochloric acid is really a
solution of hydrogen ions and chloride ions in water.
Now we will look at the definition
for a base. Bases are simply substances that
neutralize acids to produce a salt and water. This can be represented by the
general equation acid plus base makes a salt plus water. This type of reaction is called a
neutralization reaction. Bases are often confused with
alkalis. However, an alkali is a very
specific type of base. Not all bases are necessarily
alkalis. If a base is soluble in water and
makes a solution, then it will be an alkaline solution. Alkaline solutions contain
different ions to acidic solutions.
An example of a soluble base that
forms an alkaline solution is sodium hydroxide. In the solid state, sodium
hydroxide contains positive sodium ions and negative hydroxide ions. When sodium hydroxide is added to
water, it dissociates and releases positively charged sodium ions and negatively
charged hydroxide ions into the solution. So an alkali is a substance that
dissociates in water, producing negative hydroxide ions.
Three common bases that dissolve in
water to give alkaline solutions are sodium hydroxide, potassium hydroxide, and
calcium hydroxide. So these substances can also be
referred to as alkalis. Their formulas are NaOH for sodium
hydroxide, KOH for potassium hydroxide, and Ca(OH)2 for calcium hydroxide. Sodium hydroxide is found in drain
cleaner and oven cleaner and is also known as caustic soda. Potassium hydroxide is also known
as potash. It is also a strong alkali and very
corrosive material. Calcium hydroxide is found in lime
water.
In the next section of this video,
we will explore the idea of concentration in acids and alkaline solutions. Concentration is a way of measuring
the amount of a substance dissolved in a specified amount of water. We could obtain two beakers
containing identical volumes of water. If we added twice the number of
acid particles to one beaker compared to the other to make two solutions, then we
would say that the solution with double the number of acid particles per unit of
volume is twice as concentrated as the other solution. Another common way of comparing the
concentrations of these solutions is to say that one is dilute and the other is
concentrated.
Concentrated solutions of acids and
alkalis can be more dangerous than dilute solutions. Extra precautions must be taken
when handling concentrated solutions. When handling concentrated
solutions of acids and alkalis, goggles and protective lab aprons and gloves should
be worn.
It is likely that dilute and
concentrated solutions of acids and alkalis will carry different hazard warning
labels. These are seen in the form of
pictograms. The symbol with the exclamation
mark warns us that the solution is an irritant. The solution is harmful, but it
will not cause immediate damage upon contact with materials. The irritant warning label is most
likely to apply to dilute solutions of acids and alkalis. The pictogram showing a hand or
material eroding upon contact with a substance indicates that the substance is
corrosive. This pictogram would be found on
concentrated solutions of acids and alkalis.
Now that we have learned about
acids and bases and their chemical behavior, it’s time to look at a question.
Which of the following occurs when
a base is dissolved in water? (A) It dissociates, producing
positive hydrogen ions, which can turn a blue litmus paper red. (B) It dissociates, producing
negative hydroxide ions, which can turn a blue litmus paper red. (C) It dissociates, producing
positive hydrogen ions, which can turn a red litmus paper blue. (D) It dissociates, producing
negative hydroxide ions, which can turn a red litmus paper blue.
Now let’s remove the answer choices
to make some space for an explanation. A base is a substance that
neutralizes an acid to produce a salt and water. And bases that dissolve in water
and dissociate into ions are called alkalis. So in this question, we are dealing
with an alkaline solution. Alkalis dissociate to form
negatively charged hydroxide ions in water. An example of an alkali is sodium
hydroxide. Sodium hydroxide has the chemical
formula NaOH. When added to water, sodium
hydroxide dissolves and it produces positive sodium ions and hydroxide ions, which
are negatively charged. When negatively charged hydroxide
ions are present in a solution, we can test for them using red litmus paper. When red litmus paper is dipped
into the solution containing hydroxide ions, it will turn blue.
So to answer the question “Which of
the following occurs when a base is dissolved in water?” the correct answer is that
it dissociates, producing negative hydroxide ions, which can turn a red litmus paper
blue.
Now, it’s time to look at the key
points that we have learned in this video. Acids and bases are found in many
common products in everyday life. For example, vinegar contains an
acid and oven cleaner contains a base. Acids dissociate in water to
produce positive hydrogen ions, which turn blue litmus paper red. Bases are substances that
neutralize acids to form a salt and water. Alkalis are bases that dissociate
in water to produce negative hydroxide ions. Alkalis turn red litmus paper
blue. The concentration of an acid or
base is determined by how much acid or base is present per volume of water.
