chm 113 midterm lab quiz

be able to calculate percent error

%error = |theoretical -experimental|/theoretical * 100. %error is always positive because of the absolute value so it doesn't tell you if your value is too high or too low; a lower %error is better.

define the terms saturated hydrocarbon and unsaturated hydrocarbon

a saturated hydrocarbon is an alkane, or a hydrocarbon with only single bonds because it is saturated with the most amount of hydrogens it could possible hold. an unsaturated hydrocarbon is an alkene or an aromatic because there is at least one double bond that takes away from the amount of hydrogens each carbon could bond to.

explain the difference between precision and accuracy

accuracy is how close your measurement is to the true value. it is usually a function of the equipment you are using. precision is how close together multiple measurements are. we can also talk about precision by focusing on how many places after the decimal we can read.

describe the different chemical reactivities of alkanes, alkenes, and aromatics toward bromine and potassium permanganate

alkenes react with bromine to turn from yellowish (from the bromine) to clear. this is because the compound changes from an alkene to a halogenated alkane. alkanes react slowly with bromine in the presence of heat or light to from an alkane with a bromine attached. aromatics do not react with bromine. alkenes react with potassium permanganate to form a diol, removing the purple color from potassium permanganate and forming ugly brown precipitate instead.

attire and personal protection when handling chemicals

all personal belongings should be stored away from the lab work area. approved safety goggles must be worn by everyone in the lab. one must wear closed toe shoes and long pants or full-length skirts that cover the ankles. do not fill a pipette with mouth suction. do not pour water into a concentrated acid. never return unused chemicals to the bottles. never smell a chemical, only waft the vapor. do not take chemical bottles to your desk.

classify a hydrocarbon as an alkane, alkyne, or aromatic based on its chemical structure

an alkane has only single bonds and is saturated. alkenes contain one or more carbon-carbon double bond. both of these can by cyclic or straight. aromatics contain at least one ring compound, most often a benzene ring. this is a six carbon ring with alternating double bonds.

calculate densities of solids and liquids from measurements of mass and volume; and calculate mass and volume quantities by applying the definition of density.

d = m/v, can also be arranged to be m = d*v or v = m/d. units are typically g/cm^3 or g/mL

note whether hydrocarbons are soluble in water or dichloromethane

hydrocarbons are not soluble in water but will dissolve in dichloromethane.

identify a hydrocarbon using a combination of physical and chemical properties

hydrocarbons are not soluble in water. they are easily flammable. they are often, though not always, liquids. they are less dense than water and nontoxic. alkanes are colorless, tasteless, and odorless

perform calculations using two well-known gas laws - the ideal gas law and avogadro's law - to determine the molar mass of an unknown gas

ideal gas law: pv=nRt. can also be written as pv=(m/M)rt or rearranged to M=mrt/pv. r is usually 0.0821 when the pressure unit is atm. avogadro's law is v1/n1 = v2/n2. it can be simplified to n1 = n2 when the volume is held the same, and rearranged to m1/M1 = m2/M2. both substitutions used the equation n = m/M

accidents and emergencies

in case of a chemical burn, flush the area immediately with cold water and have another student summon the instructor. summon the instructor immediately in case of any accident. eye wash stations are located at the ends of certain lab benches and the safety shower is outside the lab.

be familiar with common laboratory equipment

laboratory glassware is typically made of borosilicate glass. common pieces of equipment include: beaker, erlenmeyer flask, filter flask, brushes, glass funnel, 150* thermometer, hot hands, test tube, magnetic stir bar, pipette bulb, volumetric pipet, graduated cylinder, round bottom flask, volumetric flask, watch glass, buchner funnel, graduated pipette, glass stir rod, metal spatula, test tube clamps, water bottle, separatory funnel, syringe with nail, buret

be able to report numerical values using the correct number of significant figures.

leading zeroes are always insignificant, trapped zeroes are always significant, and trailing zeroes are sometimes significant. trailing zeroes are significant when there is a decimal point. in addition and subtraction calculations, you report answers with the number of places following the decimal. in multiplication and division calculations, you report the answers to the least number of sigfigs given

top-loading balance

less precise, used when working with high masses or where exact quantities aren't critical

calculate the concentration of a solution in molarity.

molarity is m/L. this can be determined by measuring the amount of moles dissolved in a certain volume of solution. you can also determine this by getting the mass of a solution and then converting that into moles before placing that over the volume of a solution for concentration.

beaker

most common piece of glassware, primarily used for mixing and heating and stirring. should not be used for measuring

distinguish between physical and chemical changes

physical changes are changes that do not alter a substance's chemical identity. these could be state changes, mixing, crushing, etc. chemical changes change a chemical's identity. this could be production of a gas, denaturing protein, neutralizing an acid or base

erlenmeyer flask

piece of tapered glassware well designed for mixing via swirling by hand, should not be used for measuring

personal conduct and preparation

smoking, eating, or drinking in the laboratory is forbidden. acts of mischief are forbidden. chemicals and equipment may only be handled in prescribed ways for prescribed purposes. "playful" activities are not tolerated.

volumetric pipet

specialized piece of glassware designed to dispense very precise and accurate volumes of a solution

volumetric flask

specialized piece of glassware designed to prepare and contain solutions of a very precise and accurate final volume (useful in dilutions)

graduated cylinder

tall, narrow piece of glassware designed for measuring volume of liquid. precision depends on graduated cylinder

burette

tall, thin piece of glassware designed to measure the volume of a solution that is dispensed, typically to two decimal places

laboratory operations

the floor should be kept free of slipping hazards. insoluble materials falling into a sink or drain should be removed immediately. clean off the desk top thoroughly at the end of the period and all gas outlets or water faucets should be turned off. spilled chemicals and broken glassware should be cleaned up as soon as possible. dispose of chemicals in their proper waste containers and never down the drain unless you have express permission. always obtain the instructor's permission before performing an experiment not in the lab manual. do not work in the laboratory unattended.

recognize the relationship between the digits in a measured number and the certainty of the measurement. when taking a measurement, how do you determine the last digit in the number you report?

the last digit of the measurement is the degree of uncertainty. when measuring something, you estimate the last digit to the closest thing you can.

what is the difference between the terms solute, solvent, concentrated, and dilute

the solute is what is dissolved. the solvent is doing the dissolving. more simply, the solute is whatever there is less of. concentrated means there is a large concentration of solute in a little bit of solvent. dilute means there is little solute in a lot of solvent. concentrated and dilute are qualitative terms. concentration is describe quantitatively using molarity, or m/L

analytical balance

used to measure to a high level of precision, has doors around the pan to protect from drafts that may affect the measurement

properly measure and report values of length, volume, mass and temperature using common laboratory instruments.

volume should be measured arbitrarily with a graduated cylinder or burette. it should be measured precisely with a volumetric flask or pipette. mass should be measured precisely with an analytical balance and arbitrarily with a top-loading one. length can be measured with a ruler, and temperature with a thermometer (properly calibrated). standard unit of volume is the L, but in lab we use mL and cm^3. standard unit of mass is the kg but we use g. standard unit of length is m, but we use cm or mm. standard unit of temperature is *C

understand the approach used in a serial dilution to prepare a very dilute solution from a concentrated one. be able to perform the necessary calculations.

when performing a serial dilution, determine the intermediate dilution factor. dilution factor is the ratio of how much you start with to how much you dilute it to. diluting 10 mL to 50 mL is a 1:5 dilution factor. the equation used is m1v1 = m2v2. this equation can be rearranged to m2 = m1 (v1/v2). in this case 2 is the final and one is the initial. in a serial dilution, you will use this equation twice. the first time, the initial is what you start with and the final is your intermediate solution. the second time, the initial is your intermediate solution and the final is the desired end.

describe the relationship between density and layering of objects that do not mix

when two objects do not mix, like oil and water, they sit on top of each other in two separate layers. the less dense object will sit on top of the more dense object because the more dense object gets pulled to the bottom of the container. it is similar to a rubber ball floating on water because it is less dense.