5B2 pH Flashcards
Perform pH, pOH, and ion concentration calculations for acidic and basic solutions.
What does ‘pH’ stand for?
Potential of hydrogen
The pH of a solution indicates the concentration of hydrogen ions (H⁺) in a solution.
Which scientist introduced the concept of pH?
Søren Peter Lauritz Sørensen
He introduced the pH scale in 1909 while working for a beer company.
Which scale is used to measure the acidity or basicity of a solution?
The pH scale
The pH scale ranges from 0 to 14.
Values below 0 or above 14 can occur, but they are rare.
Define:
pH
mathematically
pH = -log [H⁺]
This equation relates pH to the hydrogen ion concentration, where [H⁺] represents the concentration of hydrogen ions.
What is the pH of a neutral solution?
7
Neutral solutions have equal H⁺ and OH⁻ ions.
Fill in the blank:
Acids have pH values ____ than 7.
less
Acids are represented by pH values from 0 to 6.
Fill in the blank:
Bases have pH values ____ than 7.
greater
Bases are represented by pH values from 8 to 14.
Which equation is used to calculate pOH?
pOH = -log [OH⁻]
This equation calculates pOH based on hydroxide ion concentration.
How do you calculate pOH from pH?
pOH = 14 - pH
The sum of pH and pOH in a solution is always 14.
How does the pH scale relate to the concentration of H⁺ ions?
It is logarithmic; each pH unit change represents a tenfold change in H⁺ ion concentration.
For example, a pH of 6 has ten times the H⁺ ion concentration of a pH of 7.
What is the estimated pH of a solution with [H⁺] = 4.6×10^-5?
Between 4 and 5.
The exponent provides a rough estimate of the pH range.
True or False:
A solution with pH=2 is a strong acid.
True
Strong acids have pH values closer to 0.
What does [OH⁻] represent?
The concentration of hydroxide ions in moles per liter (M).
It quantifies the basicity of a solution.
Which pH value range represents strong bases?
12–14
Strong bases are far from the neutral value of 7.
True or False:
pH can be a negative number.
True
Extremely high [H⁺] can result in negative pH values.
What does the negative sign in the pH formula accomplish?
It makes the pH value positive when the H⁺ concentration is less than 1.
Since [H⁺] is often less than 1, the logarithm of [H⁺] is negative, and the negative sign inverts it.
What happens to the pH when H⁺ ion concentration increases?
It decreases.
The pH scale inversely reflects the concentration of H⁺ ions; higher [H⁺] means lower pH.
Calculate the pH of a solution [H⁺] = 10^-5.
pH = 5
The pH is the negative logarithm of the hydrogen ion concentration.
pH = -log [H⁺] = -log(10^-5) = 5
What is the pH of a solution with [H⁺] = 10^-7?
pH = 7
This is the pH of neutral water, where [H⁺] and [OH⁻] are equal.
What type of relationship does a logarithmic scale represent?
A non-linear relationship between data.
Each unit change on the x-axis corresponds to a tenfold change on the y-axis. This is true for the pH scale or the Richter scale that measures earthquake intensity.
Fill in the blank:
[H⁺] multiplied by [OH⁻] equals _____.
1×10^-14
This is the ion product of water (Kw).
Fill in the blank:
The lower the pH value, the _____ the acidity.
higher
Lower pH indicates higher [H⁺].
What happens to basicity as pH decreases?
It decreases.
A lower pH indicates lower [OH⁻].
What is the pH of a solution with [H⁺]=1×10^-3?
pH = 3
This is calculated using pH = -log [H⁺].
What is the hydroxide ion concentration [OH⁻] if pH is 12?
[OH⁻] = 0.01 mol/L
Use:
pOH = -log [OH⁻]
pOH = 14 - pH
List three examples of acids commonly found in households.
- Vinegar
- Citrus fruits
- Soda
These acids are examples of substances with a pH less than 7.
Which household item typically has a basic pH?
Dish cleaner
It has pH > 7, indicating basicity.
List three uses of the pH scale outside chemistry labs.
- Medicine
- Environmental science
- Agriculture
These fields rely on pH to make informed decisions.
How is pH relevant in agriculture?
It helps analyze soil concentration for plant growth.
Farmers use pH to optimize soil conditions.
List three methods of determing the pH of a solution.
- pH meters
- pH indicators
- Reactivity with metals
Which method is most accurate for determining the pH of a solution?
pH meter
pH meters directly measure hydrogen ion activity and provide precise readings.
What is the role of the glass electrode in a pH meter?
It develops a charge correlating to hydrogen ion activity.
The pH meter uses the charge difference between electrodes to determine pH.
What is the color of a solution with pH 4 on a universal indicator?
Orange or red
The color represents its acidic nature.
Which pH indicator turns acids red and bases blue?
Litmus paper
Litmus paper is a common pH indicator used in laboratories and households.
How does phenolphthalein behave in the presence of a base?
It turns pink.
Phenolphthalein is colorless in acids and neutral solutions but turns pink in basic solutions.
What color does methyl orange turn in an acidic solution?
Red
Methyl orange is commonly used in titration to indicate acidity.
True or False:
Conductivity meters can be used to determine whether a substance is an acid.
True
Conductivity meters measure electrical current, which depends on ion concentration.
What is the key limitation of pH indicators like litmus paper?
They do not provide exact pH values.
pH indicators only show whether a substance is acidic, basic, or neutral through color changes.
What reaction occurs when acids interact with active metals like zinc?
Hydrogen gas (bubbles) is released.
Acids displace hydrogen ions, forming hydrogen gas and a metal salt.
