BIOL-141L Midterm Study Guide

solution

a homogenous mixture of one substance (the solute) dissolved in another substance (the solvent)

solvent

water or other dissolving agents

solute

dissolved particles (chemicals, sugar, salt, dye)

concentration of a solution

reflects a ratio of the amount of solute to the amount of solvent

Dilution

the process of reducing the concentration of a solute in a solution by mixing it with more solvent.

• the solute/solvent ratio decreases because the volume of solvent increases

many commercially available solutions are provided as _ (_) _ and need to be _ to _ _ prior to use

concentrated (stock) solution, diluted, lower concentration

Formula to determine how much stock to use and what each variable stands for

V1 C1 = V2 C2

• V1 = starting volume of concentrated (stock) solution needed to make the diluted (new) solution

• C1 = starting concentration of concentrated (stock) solution

• V2 = final volume of diluted (new, working) solution

• C2 = final concentration of diluted (new, working) solution

Formula for determining how much water (or other solvent) to add

V solvent = V2 - V1

Dilution factor (DF)

Represents how much the concentration of solute has decreased in the diluted concentration from the stock

Dilution factor formula

DF = V1/V2 = V1/V1+V solvent = Starting volume of stock/(Starting volume of stock + Volume of solvent)

Serial dilutions

Preparation of successive dilutions

• Vary the concentration of the solute by a constant factor

• Each successive dilution is a multiple of the previous dilution

How to find the final dilution factor in the last cup (from the stock) in a serial dilution:

Multiplying the dilution factors of each solution

• Ex: DF1 = 1/10, DF2 = 1/10

• Final DF = 1/10 × 1/10 = 1/100

Dilution factors have no units as they cancel out!

How is the total volume in serial dilutions distributed?

Each tube usually has 9mL (or whatever unit) of volume, while the transferred volume from each tube is 1mL (or whatever unit).

Dilution factor/Final concentration table example

Serial dilution diagram/drawing example

** The concentration in each dilution tube is _ on the _ _ of the _ !
+ example

dependent;original concentration;stock

• Example: If you started with a 10M NaCl stock concentration instead of a 1M stock concentration, tube A would have a 1M NaCl concentration, tube B would have a 0.1 M (10^-1) NaCl concentration, and so on.

  • The dilution factors would be the same if all were 1/10 dilutions, but the concentrations would be different. This concept is very important to know.

General lab safety guidelines

• long pants/skirts and closed-toe shoes during lab

• clothes should fully cover the stomach

• no food or drink allowed in classroom

• follow/ask instructor for any directions/disposal directions

• no druggies (against law)

• store materials in cubby prior to lab

• masks wearing is the student’s choice

• gloves on as soon as u enter and they go in the TRASH

• no excessively long nails

• students can request goggles

• ur materials bin is shared with one lab partner (or two if odd number)

• must use disinfectant solution provided to spray down lab station before AND after each lab

• use alcohol pads to wipe down microscope if it is being used

• do not remove any chemicals or organisms or materials from the lab

• know the locations of the chemical waste disposal container, glass waste bin, biohazard disposal bin, first aid kit, fire extinguisher, eye wash basin, and shower.

Graduated cylinders (what is it used for, how is volume measured)

• Used to measure volumes of liquids in the mL range

• Due to surface tension (adhesive properties), the surface of the water takes a concave shape

• Volume is measured by reading the bottom of the meniscus line

  • Plastic cylinders don’t usually have as prominent a meniscus as the glass ones

10mL graduated cylinder (how to read it)

• Each line represents 0.1 (9-liner) mL or 0.2 mL (4-liner) volumes (depends on the cylinder)

• 1 or 2 mL increments have large numbers to indicated volume (depends on the cylinder)

100mL graduated cylinder (how to read it)

• Each line represents 1 mL volume with slightly larger lines that represent every 5 mL

• 10mL increments have large numbers to indicate the volume

Serological pipettes (used for what; common pipette sizes)

Used to more accurately transfer volumes of liquids and can measure volumes from 1-25 mL

• Common pipette sizes: 1mL, 5mL, 10mL, 25mL

• Need to use a pipetting aid/pump to draw up and dispense the liquid

How to read a 10mL serological pipette

• Each pipette has large numbers running from 9 to 0 (bottom to top) that each represent 1 mL volumes

• Often, they have smaller numbers in the opposite order on the other side

  • Smaller lines represent every 0.1 mL volume

Rules for pipetting (5): Serological pipette

• Draw up and dispense the liquid slowly

• If air bubbles appear, while drawing the liquid into the pipette, dispense the liquid and do it again

• Do NOT let the liquid go up into the cotton, it will prevent the pipette from working

• If there is liquid in the pipette, do not place it down on the counter or hold it upside down

• Always double check your volume after removing the tip from water (will often drop)

Micropipettes (used for what)

Used to measure microliter volumes of liquid from 0.1 to 1000 μL (≤ 1 mL)

• Used with disposable pipet tips

• Each measures volumes in a specific range

Micropipettes (Common pipettes and HOW to read the volumes)

• P-1000: for 100-1000 μl

• P-200: for 20-100 μl

• P-100: for 10-100 μl

• P-20: for 2-20 μl

• P-10: for 1-10 μl

Look at number of boxes on pipettes and whether there is a decimal point on them or not!!

Reading volumes on dif. types of micropipettes: Values in between integers

• Each smaller line gives one extra unit of measurement

• Line increments by pipette type:

  • P-20: every 0.02 μl (0.02, 0.04, 0.06, 0.08)

  • P-200: every 0.2 μl (0.2, 0.4, 0.6, 0.8)

  • P-1000: every 1 μl → last unit big number is either 0 or 5

For pipettes read vertically, a reading of “015” means:

• 150 μl on a P-1000

• 15.0 μl on a P-100/P-200

• 1.50 μl on a P-10/P-20

Micropipette use: Drawing up the liquid steps

• 1: Twist plunger/dial to desired volume

• 2: Add disposable pipette tip

• 3: Press plunger to first stop

• 4: To draw the water up, put the tip into the water

• 5: Slowly release plunger to go back to the rest position

  • Pause for a moment to make sure all of the liquid has been drawn up

Micropipette use: Dispensing the liquid

• 1: Pull the pipette straight out of the tube

  • Make sure there is no bubbles

• 2: Move the pipette to the empty tube

• 3: To dispense liquid, press plunger (SLOWLY) past first stop to second stop

  • Touch the side of the tube (it is difficult to dispense the liquid in the air)

• 4: Keep plunger down as you remove the pipette

• 5: Eject tip: Push the tip eject button

Rules for pipetting: Micropipette

• Never use a pipette without a tip on it

• Never lay down or turn upside down a pipette that has a tip filled with liquid

• Never rotate the volume adjuster beyond the upper / lower range of the pipette

• ALL OF THESE MISUSES CAN DAMAGE THE PIPETTE

Digital scales (solid measurements) buttons’ meaning:

• ZERO: used to tare the balance as well as turn the power on or off

• UNIT: used to change the unit of mass you want to measure

Physical quantities in science are expressed using _ units and using the _ system.

SI (International System of Measurements); Metric

SI Units chart (Property, Unit, Symbol)

→ also Property: volume, Unit: liters, Symbol: L

Prefixes for Metric system (Prefix, Symbol, Base unit multiplied by…, Example)

Conversion rates!!

• 1 km = 1,000 m

• 1 m = 1,000 mm

• 1 m = 100 cm

• 1 m = 1,000,000 μm

• 1 m = 1,000,000,000 nm

• 1 m = 10 dm

MAKE SURE THE STARTING UNIT ALWAYS CANCELS OUT IN DIMENSIONAL ANALYSIS!!

Scientific notation

Useful way to express very large or very small numbers

ex: Avogadro’s number: 6.02 × 10²³ m

Scientific notation: numbers less than 1

• Move the decimal rightward to the first digit and count the number of places

Scientific notation: numbers more than 1

• Move the decimal leftward to the first digit and count the number of places

Conversion rate between two dif. units FORMULA

value you are starting with * (conversion rate of the unit you want to end up with) / (conversion rate value of the same unit you are starting with) = value with the unit you want to end up with

Molarity formula (and corresponding moles of solute formula)

Molarity (M or mol/L) = Moles of solute / Volume of solution in Liters

• Moles of solute: mass of solute (g) in given problem / molar mass of solute (g/mol) → g cancels out, leaving us with mol!

Molarity: one step approach (Formula to solve for mass of solute needed to make a solution)

number of grams solute = molar mass * desired molarity * desired volume (L)

Molarity: two step approach

1) solve for moles of solute using molarity equation → Rearrange equation to solve for moles → moles = Molarity * volume (L)

2) solve for mass of solute using molar mass conversion → moles solute * (molar mass solute (g) ) / 1 mol solute = mass (g) of solute to weigh out

How to properly dilute without overshooting volume

1) add less than needed volume of solvent to beaker/cylinder

2) add solute and mix

3) slowly add more solvent until expected volume is reached, then mix

Water can dissolve _ _ _/_ because it is a _ _.

polar covalent molecules/ions ; polar molecule

Polar covalent solutes (and examples)

• Dissolve by separating into individual molecules and forming hydrogen bonds with water

• Ex: simple sugars like glucose

Ionic solutes (and examples)

• Dissociate into fully-charged ions (ex: NaCl: Na⁺, Cl^-), held in solutions by electrostatic/ionic interactions in water

Electrolytes (+ examples)

Solutions containing free ions that can conduct electricity

• Ex: Gatorade, body fluids

Conductivity rule

The more ions in a solution, the higher its electrical conductivity

What does pH measure?

Acidity and alkalinity based on hydrogen ion concentration or [H⁺] ← brackets represent concentration

pH formula

-log₁₀[H+]

[H+] is the molar concentration of hydrogen ions

Hydroxide ion

[OH^-]

• higher hydroxide ion concentration in a solution means it is more basic, and higher hydrogen ion concentration in a solution means it is more acidic

DI / Deionized water

Filtered to remove ions, but atmospheric CO₂ dissolves in it to form H⁺ ions over time, which affects its pH and conductivity

Acidic pH

pH < 7 ( [H⁺] > [OH^-] )

Basic pH

pH > 7 ( [OH^-] > [H⁺] )

Neutral pH

pH = 7 ( [OH^-] = [H⁺] )

at any pH, the logarithmic sum of concentrations is…

14

• log[H⁺] + log[OH^-] = 14

How to calculate pH from [H⁺]

pH = -log[H⁺]

How to calculate [H⁺] from pH

[H⁺] = 10^-pH

An example of a strong acid is _ because it…

An example of a weak acid is _ because it…

HCl (hydrochloric acid); completely dissociates (ionizes) into H⁺ and Cl^- ions, lowering the pH.

H₂CO₃ (carbonic acid) ; only partially dissociates (ionizes) into ions (H⁺ and HCO₃^-), not lowering the pH but instead slightly raising it.

An example of a strong base is _ because it…

An example of a weak base is _ because it…

NaOH (sodium hydroxide) ; completely dissociates into Na⁺ and OH^- ions, raising the pH.

NH₃ (ammonia) ; only partially ionizes in water to form OH^- ions, not raising the pH but instead slightly lowering it.

A 1-unit increase in pH = a _-_ _ in [H⁺].

10-fold decrease

• Vice versa, a 1-unit decrease in pH = a 10-fold increase in [H⁺].

Buffers

Chemicals that react with H⁺ or OH^- to resist changes in pH.

By diluting HCl (a strong acid) in water, the pH of the solution should _, by diluting NaOH (a strong base) in water, the pH of the solution should _.

increase ; decrease

If the conductivity meter lights both the green and red lights considerably, this means that the solution has _ conductivity and there is a _ concentration of ions present in the solution.

high ; high

High conductivity is typically associated with _ bonds, while low conductivity is typically associated with _ bonds and _ forces.

ionic ; hydrogen ; intramolecular

Ions do not dissociate from glucose when it is dissolved in water because _, and thus it has _ conductivity.

Glucose (C₆H₁₂O₆) is held together by strong covalent bonds rather than ionic bonds, and instead forms hydrogen bonds with water (H₂O) molecules without any ionization occuring. ; low

Diluting any aqueous solution with DI (Deionized) water moves its pH closer to the pH of _ _ which is _.

Pure water ; neutral (~7, although the pH of pure DI exposed to air is ~ 5-6).

Monosaccharides (reducing sugars): reagent and test

Benedict’s solution

• Solution heated for 3-5 mins in boiling water

Positive test: Monosaccharides (simple carbohydrates, reducing sugars)

Color gradient change from light blue/green → yellow → orange → brick red

• The more the color changes, the more abundant the solution is in monosaccharides

Negative test: Monosaccharides (simple carbohydrates, reducing sugars)

Solution remains a light blue/green

Starch (polysaccharide, complex carbohydrate): reagent and test

Iodine dye

• Solution shaken for 30 seconds after complete addition of solvent/all solutes

Positive test: Starch (complex carb.)

Dark blue solution

Negative test: Starch (complex carb.)

Bright yellow solution

Lipids: reagent and test

Sudan IV dye

• Solution shaken for 30 seconds after complete addition of solvent & all solutes; look at the meniscus

Positive test: Lipids

Concentrated scarlet red droplets at meniscus, reddish solution

Negative test: Lipids

Solution is a uniform pink

Proteins (Biuret test): reagents and procedure

Sodium hydroxide (NaOH; added first to ensure the peptide bonds in the proteins lose hydrogen atoms) and copper sulfate (CuSO₄)

• Solution shaken for 30 seconds after complete addition of solvent & all solutes; let precipitate settle before reading

Positive test: Proteins

Solution is a violet/purple liquid above the precipitate

Negative test: Proteins

Solution is clear above the precipitate

Vitamin C (ascorbic acid)/citric acid: reagent and test

Indophenol dye

• Added drop-by-drop, and the test tube is shaken after each drop

Positive test: Vitamin C/citric acid

Color gradient change: Dark blue → transparent + colorless

• The more the color gradient changes, the more abundant vitamin C is in the solution

Negative test: Vitamin C/citric acid

No color gradient change, with the solution remaining a dark blue

Positive control

Produces a known and expected result; and proves that the experimental setup is able to produce a measurable outcome; prevents false negatives

Negative control

No response expected; uses solvent/placebo like water; prevents false positives

Scientific process order

Observation → question → hypothesis/explanation → prediction → experiment → results → analysis/conclusion → peer review

Observation

Objective info gathered directly from senses

Hypothesis

A tentative, testable, falsifiable explanation for the scientific observation or phenomenon

Prediction

An expected outcome of a specific test if the hypothesis is true, usually in the form of an “If...Then…” statement

Independent variable

The factor intentionally changed / manipulated by the experimenter

• Plotted on X-axis

Dependent variable

The factor being measured / observed that changes in response to the independent variable

• Plotted on Y-axis

Experimental group

The group receiving the treatment/manipulation

Control group

The baseline group kept under normal conditions (given a placebo / not given the treatment or manipulation) to compare results

Controlled variables (Constants)

Factors kept strictly identical across all groups to isolate the independent variable’s effect

Line graph

Shows continuous change over time

Scatter plot (Study image!!)

Displays the relationship / correlation between two continuous variables

Scatter plot: positive correlation

As the x-variable increases, the y-variable also increases

Scatter plot: negative correlation

As the x-variable increases, the y-variable decreases

Bar graph

Compares distinct categories/discrete groups

Pie chart

Shows proportions / percentages of a whole

Linear graph relationships

The rate of change between variables is constant, producing a straight line (y = mx + b)

Non-linear graph relationships

The rate of change varies, resulting in a curved line (e.g., exponential growth)

Quantitative graph descriptions

• Describing data trends using specific numeral values and rates rather than vague descriptions

• Ex: "As temperature increased from 20°C to 40°C, reaction rate doubled from 2.5 g/s to 5.0 g/s," rather than "Reaction rate went up."