Chem 1LC Safety Section - Practical, Chem 1LC practical: Technique, Chem 1LC practical: safety

Color Wavelengths Wheel

RAMP

R - Recognize

A - Assess

M- Minimize

P - Prepare

GHS symbols

Explosive, corrosives, flammables, environmental hazards, oxidizers, toxins (acute), irritants, gasses (pressure), specific toxicity

Senitizer

Chemical that causes significant allergic reaction in normal tissue upon repeat exposure

Poison

Fatal to human health

Toxic

Causes adverse human reaction in tissue

Corrosive

Destroys living cells

Flammable

Easily ignites or burns

Volatile

Liquids that vaporize easily

Oxidizer

Rapidly oxidizes, receives/donates electrons during oxidation

Gas

Gas under pressure

Precision

The reproducibility of a measurement; calculated by average deviation or standard deviation

Accuracy

The closeness of a result to the true value; calculated by percent error

GHS Symbols and NFPA Fire Diamond

Fatal - Health

Aquatic toxicity - No NFPA

Oxidizer - Special Hazard

Carcinogen & Toxic - Health

Flammable - Flammability

Irritant - Health

Explosive - Instability

Gas under Pressure - No NFPA

Corrosive - Health

SDS

- 0.1% known chemicals have safety data sheets

- Chemical suppliers creates SDS

- SDS are not required to be accurate, one should examine SDSs from different manufacturers

- SDS are written for an industrial setting, because of this chemicals hazards and personal protective equipment requirements may be overstated

Steps for using SDS

- Compare label info

- Determine the hazard class

- Look at the procedures

In the event of a spill

- If splashed with a large quantity of a chemical, use the shower immediately

- Eyewashes should be used for at least 15 minutes

- Contaminated clothing must be removed and treated as waste

- Use a small brush and dustpan when cleaning up a solid

- Use a spill pillow to absorb liquids with nontoxic vapors

- If solid is spilled on skin wash scrape off, then wash with water

Handling a corrosive

- Wear PPE

- If exposed wash off skin immediately

- Carry bottles in secondary containers

- Wear long sleeved shirts

- Use the fume hood

- Discard gloves

- Know the location of eyewash/shower

Sodium and potassium hydroxide

- White pellets

- Dissolve exothermically in water

Ammonium hydroxide

- Ammonia gas dissolved in water

- Saponify the skin which may not be immediately painful

- Skin do not form protective layers when corroded by bases

Random error

- Reduced by using a best-fit line

- Measured by calculating estimated standard deviation

Instrumental error

- Inaccurate calibration

- Light source on the visible spectrometer dims over time

Methodological error

- Consistently reading

- Using a graduated cylinder instead of volumetric glassware to make standard solutions

Systematic error

- Eliminated by good experimental methods and more than 1 calibration step

Gross error

- Result of equipment failure

- Causes outlier than can be determined by the "Q-test"

Which of the following play significant roles in the extent of injury or harm when exposed to a hazardous chemical?

- How the chemical entered the body

- The amount of chemical one is exposed to

- The amount of time one is exposed to the chemical

Which of the following are parts of the design of laboratory ventilation?

- Hallway air flows into the lab

- Air enters the labs through heating/cooling ducts and hallway air

- Lab air leaves the lab through the fume hoods

Mists

Tiny droplets of liquid suspended in air

Fumes

Colloidal suspension of solid or liquid particles in air

Dusts

Solid particles suspended in air

Smoke

Mixture of dry particles and droplets of liquid

Nanoparticles

Ultrafine homogeneous particles ranging in size from 1 to 100 nm

Why is lambda max significant?

- The value can indicate the observed color of solution

- The value is can be used to identify a particular chemical

- The instrument response is highest at that wavelength

Fire Class

A - Paper, clothing, plastic

B - Gasoline, oil, organic

C - Hot plates, computers

D - Reactive metals

Fire

- Removing heat keeps the fuel from vaporizing

- Water cannot be used to extinguish a Class D fire

- The fuel must be vaporized to burn

Bleach

- If spilled, shower

- Nitrile gloves are have a 480 min breakthrough time for bleach

- Bleach can cause severe skin burns and eye damage

- Bleach forms poisonous chlorine and chloramine gas when combine with ammonia

Graduated (Mohr pipet)

accurately transfer small variable volumes

Volumetric pipet

Accurately transfer small fixed volumes

Buret

Accurately transfer and measure variable volumes

Beaker

Contents must be easily accessed

Erlenmeyer flask

Prevent splashing or evaporation

Volumetric flask

Make and store solutions of known concentration

If you are on fire

- Stop, drop, roll

- Wrap the person in a fire blanket

PASS

- Pull: the safety pin near the handle

- Aim: the extinguisher at the base

- Squeeze: the handle to begin

- Sweep: the discharge back and forth

Fire tetrahedron

- Heat: pour water on the fire

- Oxygen: CO2 fire extinguisher

- Chemical chain reaction: use a halon fire extinguisher

- Fuel: keep amounts of flammable material to a minimum

Sig figs for glassware and digital balance

Glassware: all markings and estimate one extra decimal

digital balance: all digits present

dilution formula

M1V1=M2V2

visible spectroscopy

The study of the interaction of radiation from the visible part of the electromagnetic spectrum with a chemical species. Each photon has a specific energy related to a certain frequency or wavelength

visible spectrometer

Uses visible range (400 - 700nm) of electromagnetic radiation spectrum. Shines light of all wavelengths one end through cuvette w/ liquid, detector on other side measures what doesn't get through sample (what's absorbaed) -> absorption spectrum (plot of absorbance vs wavelength)

beer's law

For dilute solutions, the amount of light absorbed at a specific wavelength is directly proportional to the concentration of the solution. This relationship is called Beer's Law:

A = ε C l

A = absorbance (at λmax, no units)

ε = molar absorptivity coefficient (units = L/mol-cm)

C = concentration of absorbing species (units = mol/L)

l = path length (units = cm)

can be used to create a beer's law plot calibration curve of absorbance vs concentration (y vs x)

calibration curve

A graph showing the value of some property versus concentration of analyte. When the corresponding property of an unknown is measured, its concentration can be determined from the graph.

what wavelength is used for creating beer's law plot

lambda max with the highest absorbance since it maximizes the sensitivity of the spectrometer and minimizes errors

also used to determine chemical species

accuracy

the closeness of a measurement to the true value.

as opposed to precision

precision

a measure of how close a series of measurements are to one another (how reproducible)

linear precision determined from R^2

as opposed to accuracy

what blank for determining lambda max of dye

The solvent: water

why is blanking necessary

So that the visible spectrometer won't pick up the light absorption of the solvent and cuvette-only that of the solute of interest

What to do before measuring absorbance of cuvette using visible spectrometer. Why?

Blank using solvent: So that the visible spectrometer won't pick up the light absorption of the solvent and cuvette-only that of the solute of interest

wope outside of cuvette using Kimwipe and tap to remove bubbles: removing smudges/contaminants/bubbles is necessary so that nothing interferes with the visible spectrometer as it's measuring the absorbance of the solute.

using a volumetric pipette

pre-rinse using the liquid to be transferred

pipette up above calibration marking using bulb, clamp finger over top

release finger until bottom of liquid's meniscus is in line with calibration marking

release liquid into container, touch off any hanging drops but DON'T BLOW OUT LAST DROPS!

Beer's law plot visible spectrometer settings

little clock screen

sensors > data collection

> Events with Entry:

- name: concentration

- units: µM

SET WAVELENGTH TO LAMBDA MAX! (clock red screen and change wavelength)

beer's law plot graph

a calibration plot to determine concentration using a solution's (with unknown concentration) absorbance at its lambda max

y axis (dependent): absorbance

x axis (independent): concentration (make sure good spread and precise)

R^2 shows precision of linear relationship: how closesly follow line of best fit

How to determine precision for creating solutions for beer's law plot?

since precision is a measure of how close a series of measurements are to one another, it can be determined from how closely the solutions follow the linear beer's law relationship:R^2 closest to 1

what does y intercept of beer's law plot indicate

The extrapolated absorbance when there's a concentration of zero. Should be zero but due to smudges and stuff, could be positive or negative- negative: not blanked, not zeroed, tech error?- positive: too much absorbance: smudges, blanking/zeroing error

determining absorbance from beer's law plot

y = mx + b

where y is absorbance and x is concentration

given x, find y

either use the graph to estimate x corresponding to a given y or use line of best fit to calculate x given y

kinetics

study of speed/rate of a chem RXN

rate law equation

rate = k [A]^x [B]^y

pseudo rate law

A + B --> C + D

Rate = k [A]^a [B]^b

set initial [A] >> [B], [A] pretty much constant cuz in excess

Rate = k'[B]^b

k' = k[A]^a

Overall order = a + b

used in order to create a rate law with a linear equation form for rate laws involving more than one reactant -> allows you to determine reaction order of one reactant at a time

integrated rate laws for zero, first, and second order

zero: [B] = -kt + [B]₀

First: ln[B] = -kt + ln[B]₀

Second: 1/[B] = kt + 1/[B]₀

plots:

zero: [B] vs t

first: ln[B] vs t

second: 1/[B] vs t

chem RXN, rate law, and pseudo rate law for hydroxylation of crystal violet

add NaOH to CV+

CV⁺ + OH⁻ → CVOH

Rate = k[CV⁺]^x[OH⁻]^y

pseudo rate law: Rate = k1[CV+]^x where k1 = k[OH-]^y

and [OH-]₀ >> [CV+]₀

how to measure concentration of crystal violet during kinetic runs

Beer's law( A = eCl) to relate absorbance to concentration -> measure absorbance over time to indirectly measure change in concentration over time

A ~ [CV+]

azo dyes

named after their central -N=N- linkage

oxidized into two compounds: splitting at azo linkage

triarylmethane dyes

contain a center carbon ("methane") bound to three benzene rings ("aryl")

oxidize into three compounds: splitting 3 aryl groups/rings

ten-fold and two-fold dilutions

ten-fold: M1V1 = M2V2 where V1 * 10 = V2

two-fold: M1V1 = M2V2 where V1 * 2 = V2

where V2 is the volume of the end solutions, NOT THE VOLUME OF THE WATER

reduces concentration to 1/2 of 1/10 of preceding each time.

lab quest settings for kinetic plot of a dye

absorbance vs time data needed (absorbance ~ concentration according to beer's law plot)

click little clock symbol

> mod > time-based spectrum

duration: 20 mins

interval: 0.25 min/sample

rate: 4 sample/min

SET WAVELENGTH TO LAMBDA MAX OF THE DYE

blanks for determining lambda max of crystal violet

solvent: water

blanks for taking absorbance of crystal violet and NaOH mixture (or Gatorade dye and bleach NaOCl)

CV+ and NaOH: blank using water w/ appropriate NaOH solution (the standard for the given mixture)

Gatorade dye and NaOCl: blank using water w/ appropriate NaOCl solution (the standard for the given mixture)

SINCE YOU DON'T WANT TO MEASURE THE ABSORBANCE OF THE WATER OR THE NaOH OR NaOCl. DON'T BLANK USING JUST WATER

ADD SPILL KIT LAB SAFETY MOMENT 2 TO SAFETY QUIZLET!

steps for using pH probe in titration lab

Always rinse using DI water between use and pat dry gently using kimwipe, newer let dry

- test it using pH 7 buffer: should be within +/- 0.4 pH

- use to get initial pH

- use to get pH of analyte as titrant is added

titrant vs analyte

A titrant is a substance of known concentration which is added in measured amounts from a buret

An analyte is a substance of unknown concentration to which the titrant is added (in beaker)

the two titrants for the Gatorade titration lab and which one is better

NaOH strong base and HCl strong acid are provided

since gatorade is a weak acid buffer, it is a better buffer for a strong base like NaOH

Reaction of buffer in Gatorade when neutralizing added NaOH or HCl

NaOH neutralization: HA + NaOH → H2O + A⁻

HCl neutralization: B + HCl → HB⁺ + Cl⁻

equivalence point

inflection point of the titration curve (nearly vertical)

The point in the titration when exactly enough base has been added to neutralize all the weak acid that was initially present or vice versa

only products of the balanced chemical EQ are present at this point: buffering capacity reached.

buffering region

The long gradual almost horizontal incline where the pH is being buffered by the weak acid/base buffer system present

before the equivalence point

use the endpoints of the buffering region to determine buffering capacity = Δn/ ΔpH

buffering capacity

symbol: β

How well a solution can resist changes in pH when an acid or base is added.

unitless

buffering capacity = Δn / ΔpH

change in moles of titrant over change in pH of the analyte

calculated using endpoints of the buffering capacity

n = M*V

buffer

solution characterized by the ability to withstand changes in pH when limited amounts of acid or base are added to it; usually contains weak acid/base w/ the salt of its conjugate base/acid

using a digital balance

use same balance throughout experiment and don't move it

tare it using the weigh boat/paper/container that will carry the substance

close draft shields when taking measurements to prevent the outside environment from influencing the reading

Record all sig figs

titrant curve plot

y axid: dependent: pH

x axid: independent: volume of titrant added

buffering region is horizontal region before equivalence point where buffer is resisting change in pH

equivalence point is where the inflection takes place (almost vertical) and only products of the buffing reaction remain, buffering capacity met

intial: pH of the analyte (gatorade)

final: approaches pH of the titrant (strong acid or base)

using a buret

A glass tube with a uniform diameter that is mounted vertically and has a stopcock at its lower end to regulate the liquid flow.

pre-rinse, take volume by doing final - initial, measure volume released from the buret (numbering begins at top)

always let some of the liquid drain out first before adding titrant: removes bubbles trapped in the stopcock

markings to the tenth place, can estimate to the hundredth place

0.00 mL

LabQuest settings for titration

sensors > data collection

> Events with Entry:

- name: acid/base added

- units: mL

record initial, then keep after adding 1.00 mL increments of the acid/base titrant to the analyte (Gatorade)

neutralizing liquid waste

If pH is 6-8, pour the solution down the drain.

If pH is below 6, add a small amount of sodium bicarbonate. To prevent foaming over, slowly pour and stir with sodium bicarbonate addition to prevent foaming over. Recheck with pH paper.

If pH is above 8, add citric acid and recheck with pH paper.

ADD SUMMARY OF EACH PROJECT AND IN-CLASS STEMBLE STUFF!

Hazard

potential source of danger or harm

CAS numbers (Chemical Abstract Service)

Database of chemical substances

Numbers assigned by American Chemical Society

Unique and only one per chemical even if under different chemical names and formulas.

GHS: Globally Harmonized System of Classification and Labeling of Chemicals

A labeling system that uses pictograms to indicate different hazards, a signal word, a hazard statement, and supplier information.

The hazard statement is a summary of the main hazards

GHS signal words

'Danger' or 'Warning' indicating hazard severity.

warning is lower hazard severity than danger

allergen

A chemical that causes an allergic reaction - that is, can evoke an adverse immune response in a person.

Aspiration hazard

health hazard that covers products that may be fatal if they are swallowed and enter the airways

Aspiration toxicity includes severe acute effects, such as chemical pneumonia, varying degrees of pulmonary injury or death following aspiration. Aspiration is the entry of a liquid or solid directly through the oral or nasal cavity, or indirectly from vomiting, into the trachea and lower respiratory system.

Carcinogen

Chemical that causes cancer in animals or humans

Combustible

A chemical that burns under most conditions once ignited. DOES NOT ignite and burn as easily as a flammable chemical

compressed gas

a gas stored under pressure (might be liquid or gas when compressed)

corrosive

a chemical that causes destruction of living tissue at the site of contact