BI 112 – Lab #3: pH and Buffers

These flashcards cover key concepts related to pH, buffers, and their applications in the laboratory, structured to assist in exam preparation.

pH

Measures the concentration of hydrogen ions (H+) in a solution. A higher (H+) concentration indicates acidity (lower pH), while a lower (H+) concentration indicates basicity (higher pH). Easier to remember: Think 'Power of Hydrogen' - it's about how much (H+) is present.

Acids

Substances that release hydrogen ions (H+) into a solution, thereby increasing the (H+) concentration and lowering the pH. Easier to remember: 'A' for acid, 'A' for add (H+).

Bases

Substances that accept or bind to hydrogen ions (H+) in a solution, or release hydroxide ions (OH–), which effectively reduces the free (H+) concentration and raises the pH. Easier to remember: 'B' for base, 'B' for bind (H+).

Neutral

A state where the concentration of hydrogen ions (H+) and hydroxide ions (OH–) are exactly equal, resulting in a pH of 7. This is the midpoint of the pH scale. Easier to remember: Neutral is in the 'middle' at 7, a perfect balance.

pH scale

A scale, ranging from 0 to 14, that is logarithmic and indicates how acidic or basic a solution is. Values below 7 are acidic, 7 is neutral, and values above 7 are basic. Easier to remember: Imagine a ruler 0 to 14: 0 = extreme acid, 7 = middle neutral, 14 = extreme base.

Logarithmic scale

A scale where each unit change in pH represents a tenfold (10x) difference in the hydrogen ion (H+) concentration. For example, a solution with pH 3 is ten times more acidic than a solution with pH 4. Easier to remember: The 'log' in logarithmic means powers of 10. A small pH change means a BIG change in $$H+$.$.

Anthocyanin

A natural pigment found in red cabbage that acts as a pH indicator by changing color in different pH environments. It typically appears red/pink in acidic solutions and blue/green/yellow in basic solutions. Easier to remember: Think of red cabbage itself – it's red because it's slightly acidic, but add baking soda (a base) and it turns blue/green.

Phenol red

A synthetic pH indicator that exhibits specific color changes: it turns yellow in acidic solutions (pH below 6.8) and red in basic solutions (pH above 8.2). Easier to remember: Red for basic, Yellow for acidic - like a stoplight, but for pH.

Buffer

A substance or mixture of substances that resists significant changes in pH when small amounts of either an acid or a base are added. It achieves this by absorbing excess hydrogen ions (H+) or hydroxide ions (OH–). Easier to remember: A buffer acts like a 'pH cushion' or 'pH guardian,' absorbing hits to prevent drastic shifts.

Buffering capacity

The specific amount of acid or base that a buffer can neutralize before its pH begins to change significantly. It measures the buffer's effectiveness or 'strength' in resisting pH shifts. Easier to remember: Think of a sponge's 'capacity' to absorb water before it overflows; a buffer has a capacity for absorbing H+ or $$OH-$.$.

pH probe

An electronic device with a glass electrode used to measure the pH of a solution quickly and accurately, providing a digital readout. It works by measuring the voltage difference caused by the hydrogen ion concentration. Easier to remember: Think of it as a 'digital finger' that precisely reads the acidity/basicity of a liquid.

Titration

A laboratory technique involving the controlled addition of a solution of known concentration (titrant) to a solution of unknown concentration (analyte) to determine its concentration, or in the case of buffers, to observe its pH response curve. Easier to remember: Titration is like carefully 'measuring out' how much acid or base it takes to change another solution's pH.

Carbonic acid (H2CO3)

A weak acid (H2CO3) that is a crucial component of the bicarbonate blood buffer system. It acts by dissociating to release hydrogen ions (H+) when the blood pH becomes too high (basic). Easier to remember: Think of it as the 'acid side' of your blood's pH defense system, ready to donate H+ to keep things balanced.

Bicarbonate (HCO3–)

A weak base (HCO3–) that is a crucial component of the bicarbonate blood buffer system. It acts by accepting excess hydrogen ions (H+) when the blood pH becomes too low (acidic), thus preventing a drastic drop in pH. Easier to remember: Think of it as the 'base side' of your blood's pH defense system, ready to soak up excess H+.

Homeostasis

The maintenance of stable internal physiological conditions in an organism, despite changes in external conditions. For example, the body's buffering systems work to maintain blood pH within a very narrow range, which is a key aspect of homeostasis. Easier to remember: 'Homeo' means similar, 'stasis' means standing still – keeping things similar and stable inside.

Acid-base reaction

A chemical reaction involving the transfer of hydrogen ions (H+) from an acid to a base. This process often results in the formation of water and a salt, effectively neutralizing both the acid and the base. Easier to remember: It's a 'swap meet' for H+ ions, with acids giving and bases taking.

Graphing assignment

An assignment requiring students to use Excel to create a line graph of buffer titration data, plotting pH (y-axis) against the cumulative volume of acid or base added (x-axis) to visually represent buffering capacity. Easier to remember: You're mapping out how well a buffer 'fights back' against pH changes by tracking it on a graph.

Line graph

A type of graph that displays information as a series of data points connected by straight line segments, commonly used to show trends over time or, in this context, the continuous relationship between pH and the cumulative amount of acid/base added during titration. Easier to remember: A line graph helps you 'trace the journey' of pH as you add more acid or base.

Figure caption

A concise, informative description placed directly below a graph or figure. Its purpose is to explain the content, variables, and main findings of the visual, allowing it to be understood independently of the main text. Easier to remember: It's the 'storyteller' for your graph, summing up everything important in a few sentences.

Safety reminders

Essential protocols designed to ensure a safe and organized laboratory environment for all participants. Examples include disinfecting all work surfaces before and after experiments and storing personal belongings securely in designated cubbies to prevent hazards. Easier to remember: Safety is about being 'prepared and protected' – for yourself and others in the lab.

Hydrogen ion (H+)

A positively charged ion (H+) consisting of a proton. Its concentration in a solution is the primary determinant of acidity – the more (H+) present, the more acidic the solution (lower pH). Easier to remember: Think of (H+) as the 'acid booster' – more H+ means more acid.

pH indicator

A substance, often a weak acid or base, that exhibits a distinct color change over a narrow pH range. This color shift provides a visual means to estimate the pH of a solution without fancy equipment. Easier to remember: Like a 'mood ring' for chemicals, indicators change color to tell you the pH 'mood' of a solution.

pH change

An alteration in the concentration of hydrogen ions (H+) within a solution, leading to a shift in its acidity or basicity. Significant pH changes can drastically impact chemical reactions and biological processes, such as enzyme function. Easier to remember: A pH change is like a 'teeter-totter' for H+ and OH- ions – when one side goes up, the other goes down, changing the balance.

Common household items

Everyday substances readily available at home, such as lemon juice, vinegar, baking soda solution, and various cleaning products, used in Exercise 2 to explore and test pH levels with natural indicators like red cabbage extract. Easier to remember: This is where 'kitchen chemistry' meets pH – seeing how everyday items react.

Cabbage color change

The varied color response of red cabbage extract when exposed to solutions of different pH. It typically turns red or pink in strong acids, purplish in weak acids, blue-green in weak bases, and green-yellow in strong bases. This provides a clear visual indication of pH. Easier to remember: Red for 'danger' (acid), Blue for 'calm' (base), Green for 'go neutral'.

Zero pH

Represents the most highly acidic end of the pH scale. A solution with a pH approaching 0 contains an extremely high concentration of hydrogen ions (H+) and is very corrosive. Easier to remember: Think 'zero tolerance' for bases – it's pure acid.

Fourteen pH

Represents the most highly basic (alkaline) end of the pH scale. A solution with a pH approaching 14 contains an extremely low concentration of hydrogen ions (H+) and is very caustic. Easier to remember: Think 'fourteen is full' of bases – it's pure alkali.

Weak buffers

Buffers that have a limited buffering capacity and thus show more significant pH changes, or a steeper slope on a titration curve, even with relatively small additions of an acid or a base. Easier to remember: Like a 'weak shield' – it protects, but not for very long before breaking down.

Strong buffers

Buffers that exhibit a large buffering capacity, meaning they can resist substantial pH changes upon the addition of considerable amounts of acid or base. This is indicated by a flatter curve on a titration graph. Easier to remember: Like a 'strong fortress' – it can withstand many attacks (additions of acid/base) before its pH wall crumbles.

pH graphing best practices

Guidelines for creating clear and accurate pH graphs: include a descriptive title, properly labeled axes with units (pH on y-axis, cumulative volume on x-axis), appropriate scaling, a legend if multiple data sets are present, and connect data points with smooth lines to show trends. Easier to remember: A good graph is like a 'well-told story' – clear, complete, and easy to follow.

Cumulative acid/base added

The total volume or amount of either acid or base that has been incrementally added to the solution during a titration. This variable is typically plotted on the x-axis of a titration graph to show how pH changes with successive additions. Easier to remember: It's the 'running total' of how much you've changed the solution, guiding your eye along the x-axis.

Major ticks

The prominent marks on a graph's axes that indicate significant numerical values, serving to divide the scale into easily readable intervals. They help define the main units of measurement. Easier to remember: Think of them as the 'mile markers' on your graph's road, showing you the big steps in your data.

pH stability

The inherent characteristic of a solution to maintain its pH within a narrow range, largely resisting changes in acidity or basicity even upon the introduction of small amounts of acid or base. This property is predominantly due to the presence of buffer systems. Easier to remember: 'Staying strong' against pH shifts – that's pH stability.

Disinfecting tables

A crucial safety and cleanliness protocol involving the thorough cleaning of lab surfaces with an appropriate disinfectant before and after experiments. This prevents cross-contamination of samples and ensures a safe, hygienic working environment. Easier to remember: 'Clean workspace, clear mind' – essential for accurate and safe experiments.

Microscope materials

Equipment related to microscopy, such as slides, cover slips, and different objective lenses, which may be part of practical-style questions to assess knowledge of their function and proper use in observing microscopic specimens. Easier to remember: Think 'tiny worlds' – microscopes help us see details too small for the eye, and knowing their parts is key.

Lab setup essentials

Non-consumable items that are indispensable for a productive and safe laboratory session, including a lab manual or notebook, writing instruments (pen/pencil), and potentially required personal protective equipment (PPE) like safety goggles or a lab coat. Easier to remember: 'Be Prepared!' – having your essentials means you're ready to learn and work safely.

Water self-ionization

The reversible chemical reaction in which pure water molecules (H2O) spontaneously dissociate into a small, equal number of hydrogen ions (H+) and hydroxide ions (OH–). This equal production is why pure water is considered neutral, with a pH of 7. Easier to remember: Water 'breaks itself apart' equally into acid (H+) and base (OH-) parts, creating a perfect balance.

pH = 7

Specifically indicates a neutral solution. At this pH, the concentration of hydrogen ions (H+) is exactly equal to the concentration of hydroxide ions (OH–), representing a perfect balance between acidity and basicity. Easier to remember: Seven is the 'middle ground' or 'equilibrium point' where acid equals base.

pH < 7

Indicates an acidic solution. In this range, the concentration of hydrogen ions (H+) is higher than the concentration of hydroxide ions (OH–), leading to acidic properties. Easier to remember: Lower pH numbers mean 'more power' from H+ ions, making it acidic.

pH > 7

Indicates a basic (or alkaline) solution. In this range, the concentration of hydrogen ions (H+) is lower than the concentration of hydroxide ions (OH–), resulting in basic properties. Easier to remember: Higher pH numbers mean 'less power' from H+ ions, making it basic (and more OH-).

DIY pH test

A simple, cost-effective method of determining the approximate pH of various solutions by utilizing natural indicators, such as red cabbage extract, which exhibit distinct color changes based on the solution's acidity or basicity. Easier to remember: It's 'home science' for pH – using common items to see pH changes.

pH Guardian

A metaphorical term emphasizing the critical role of the body's natural buffering systems (like the bicarbonate buffer system) in vigilantly protecting against drastic pH fluctuations to maintain physiological homeostasis. Easier to remember: Imagine a 'bodyguard' for your pH, standing ready to neutralize threats (excess acid or base).

Cabbage extract

The aqueous solution derived from boiled red cabbage, containing anthocyanin pigments. This extract serves as a natural pH indicator in Exercise 2, demonstrating vivid color changes across the pH spectrum when mixed with different household items. Easier to remember: It's the 'colorful liquid tester' made from cabbage.

Buffered solution

A solution that contains a buffer system (typically a weak acid and its conjugate base, or a weak base and its conjugate acid) and is therefore capable of resisting significant changes in pH upon the addition of small amounts of strong acid or base. Easier to remember: It's a 'pH-stable' liquid, thanks to its internal buffer system working to keep things even.

Acidic solution

A solution that has a higher concentration of hydrogen ions (H+) compared to hydroxide ions (OH–). This results in a pH value less than 7 and the ability to donate (H+) to other substances. Easier to remember: 'Sour and corrosive' – typical traits of high H+ (acidic) solutions.

Basic solution

A solution that has a lower concentration of hydrogen ions (H+) and a higher concentration of hydroxide ions (OH–) compared to neutral water. This results in a pH value greater than 7 and the ability to accept (H+) ions. Easier to remember: 'Slippery and bitter' – typical traits of low H+ / high OH- (basic) solutions.

Cleanliness protocol

A set of guidelines and procedures implemented to ensure a hygienic, organized, and safe laboratory workspace. This includes practices like proper waste disposal, disinfecting surfaces, and maintaining an uncluttered work area to prevent accidents and contamination. Easier to remember: 'A tidy lab is a safe lab' – following protocols keeps everyone safer and results more accurate.

Figure due date

The deadline for submitting the graph, which is two weeks from the lab date. Easier to remember: Remember the 'two-week rule' from the lab.

10 points

The weight of the buffering capacity figure in the overall grading rubric. Easier to remember: Ten points mean it's a significant chunk of your grade.

Accurate results

Experimental outcomes that are precise, reliable, and reflect the true phenomena being investigated. Achieving accurate results depends heavily on meticulous adherence to proper lab procedures, careful measurements, and maintaining a clean environment to minimize errors and contamination. Easier to remember: 'Precision and care lead to truth' – accurate results are the goal of good science.