CHM 123 Lab Midterm Exam

NFPA Rating system

0 = most stable, 4 = most hazardous

Suppose a sample of vinegar contains 0.0685 g/mL of acetic acid, which has a molar mass of 60.052 g/mol. How many moles of acetic acid are present in a 18.4 mL solution of the vinegar?

0.0210

R

0.08206 L*atm/mol*K

How many moles of H2 can be formed if a 2.25 g sample of Mg reacts with excess HCl?

0.093

Suppose you have 450.0 mL of a 0.350 M sodium hydroxide solution. How many moles of sodium hydroxide are in the solution?

0.158

Suppose you are titrating vinegar, which is an acetic acid solution of unknown strength, with a sodium hydroxide solution according to the equation C2H3O2H + NaOH⟶ H2O + CH3CO2Na If you require 32.98 mL of 0.1776 M NaOH solution to titrate 10.0 mL of HC2H3O2 solution, what is the molar concentration of acetic acid in the vinegar?

0.586

A football field is 120 yards by 53.333 yards. What is the area of the football field in acres if 1 acre=43560 ft2? Use correct significant figures when answering this question.

1.3 acres

Percent error

100% * absolute value of: (experimental - theoretical)/ theoretical

What information does NOT need to be included a chemical waste label? Names of the chemical compounds present in the container The date the waste container was filled completely A description of the experiment the chemicals were used for Relative amounts of chemical compounds in the container

A description of the experiment the chemicals were used for

Waste Disposal: broken flask

Box lined with puncture resistant bag

Identify the precautions to take with exits in the lab. Make sure lab windows are always open. Do not block a door with an EXIT sign. Keep the exit door locked at all times. Locate the exits prior to the start of lab.

Do not block a door with an EXIT sign. Locate the exits prior to the start of lab.

When the required amount of one solution has been added to the second solution to complete the reaction

Endpoint

What should you do every time you are about to heat glassware on a hot plate? Ensure that the glassware is designed for heating Measure the height and width of the glassware Inspect the hot plate for frayed cords Check that there are no cracks in the glassware

Ensure that the glassware is designed for heating Inspect the hot plate for frayed cords Check that there are no cracks in the glassware

How do you determine the last digit in any measured number? Round up to one digit larger than the smallest precisely known digit or marking. Record the digit corresponding to the smallest precisely known digit or marking. Estimate one digit past the smallest precisely known digit or marking. Consult the unique rule for each type of lab measurement and instrument.

Estimate one digit past the smallest precisely known digit or marking.

NFPA Diamond What does red represent?

Flammability

What does a GHS picture of flames represent?

Flammable Chemical

Liquid Waste Set-Up: A

Funnel

NFPA Diamond What does blue represent?

Health

Where should glassware be stored after it is cleaned? Out on the lab bench to allow for air-drying On one side of the sink, opposite from the side where the dirty glassware is kept At the front of the lab, stacked neatly in a pile In a drying oven, or designated locations such as drawers or buret racks

In a drying oven, or designated locations such as drawers or buret racks

A reagent added to the analyte solution that changes color when the reaction is complete

Indicator

What does a GHS picture of an O with flames represent?

Oxidizing Chemical

Boyle's Law

P1V1 = P2V2

Combined Gas Law

P1V1/T1=P2V2/T2

Fire estinguisher acronym

PASS: Pull the pin, Aim the nozzle at the base of the fire, Squeeze the lever slowly, Sweep the spray from side to side over the fire

Ideal Gas Law

PV=nRT

Suppose a solution contains chloride Cl− ions. According to solubility rules, which other ion should be added to form a precipitate? Ca2+ Pb2+ CO32− Na+

Pb2+

In the Ideal Gas Law lab, how is the temperature of the hydrogen gas determined? The volume of the gas is determined, which will allow you to calculate the temperature. The temperature of the water bath is measured after the reaction, which is assumed to be the same temperature as the gas. A thermometer is inserted into the eudiometer, measuring the hydrogen gas directly. The pressure of the gas is determined, which will allow you to calculate the temperature.

The temperature of the water bath is measured after the reaction, which is assumed to be the same temperature as the gas.

Weighing by Difference Technique

a technique that involves determining and recording the mass of an empty container, then determining and recording the mass of the container + chemical; the differences between the two masses is the mass of the chemical

Eudiometer

a tube closed at one end and marked in units of milliliters

Intro to Chemistry Equipment

balance, 3 corks, weigh dish, 400 mL beaker, thermometer, 50 mL graduated cylinder, 50 mL buret, 10 mL pipet

Buret use

carefully deliver volumes of liquid and notably has a stopcock at the bottom to dispense

Density

d=m/v; g/cm^3 or g/mL for liquids; g/L for gases

Double displacement: evidence of a reaction

formation of a precipitate, of water or other small molecule, or gas

Test Tube use

hold solutions measured by other glassware or to do smaller qualitative tests

Accuracy

how close an experimental measurement is to the true, accepted value

Precision

how close repeated measurements using the same device are to each other; ability to repeat a measurement

As a solid is added to a liquid, solubility _____ as the temperature increases

increases

The relationship between pressure and volume of a gas is _____ so that as volume decreases, pressure _____

inverse, increase

Double displacement: no reaction

ion soup

Beaker use

Pouring an approximate volume of liquid into a buret; low accuracy

Liquid Waste Set-Up: B

Primary container

NFPA Diamond What does yellow represent?

Reacitivity

Liquid Waste Set-Up: D

Secondary container

Waste Disposal: Unused solid reagent

Solid waste container

NFPA Diamond What does white represent?

Special Hazards

In case of accidental contact with chemicals, how long should the eyes be flushed at the eyewash station? 5 minutes Until the irritation is gone 15 minutes 30 minutes

15 minutes

Perform the calculation, rounding your answer to the proper number of significant figures. 0.120 g + 18.0742 g=

18.194 g

Knowing that one day is 24 hours, how many days is 60.5 hours?

2.52

Acid-Base Titration Equipment

250 mL beaker, flask, 100 mL beaker, magnetic stir plate, 50 mL buret

Intro to Chemistry: equipment analyzed for accuracy (NOT the same thing as used) 10 mL Graduated Cylinder 50 mL Graduated Cylinder Thermometer Buret 10 mL Pipet Analytical Balance

50 mL Graduated Cylinder Buret 10 mL Pipet

In an experiment, the molar mass of propane was determined to be 47.07 g/mol. The accepted value for the molar mass of propane is 44.10 g/mol. What is the percent error of the experimental value?

6.73

Suppose you are measuring the mass of a solid sample on a balance using a weigh boat. You record the data in a table. Mass of weigh boat: 1.614 g Mass of weigh boat and sample 8.810 g What is the mass of the solid sample (in g)?

7.196 grams

The H2 produced in a chemical reaction is collected through water in a eudiometer. If the pressure in the eudiometer is 760.0 torr and the vapor pressure of water under the experimental conditions is 23.1 torr, what is the pressure (torr) of the H2 gas?

736.9 torr

Standard solution

A solution of known concentration/molarity

Outlier

A value that "lies outside" (is much smaller or larger than) most of the other values in a set of data.

Double Displacement/Replacement AX + BY -->

AY + BX, ion charges do not change

Significant figures

All the digits that can be known precisely in a measurement, plus a last estimated digit

Aliquot

An exact portion of a solution and is delivered using a volumetric pipet

Solution of an unknown concentration that has another solution slowly added to it

Analyte

When is the best time to clean glassware during the lab session? Once there is a sink full of items As soon as practical after use Whenever you run out of clean glassware All at once at the end of the session

As soon as practical after use

Suppose you are studying an unknown solution based on its precipitation reactions with other solutions, resulting in this data table. Unknown Na2SO4 (precipitate) NaCl (no reaction) Na2CO3 (precipitate) Which compounds might be your unknown? Select one or more: Ba(NO3)2 NaNO3 Sr(NO3)2 Pb(NO3)2 Ca(NO3)2 AgNO3

Ba(NO3)2 Sr(NO3)2 Ca(NO3)2

Determine when to put on disposable gloves for work in the lab. After setting up all the glassware but before handling chemicals Before handling any glassware or chemicals for the experiment After cleaning all the glassware for the experiment Before entering the laboratory room

Before handling any glassware or chemicals for the experiment

Glassware that allows a solution to be precisely and slowly added to another solution

Buret

What are the best practices for safely handling waste in the lab? Check labels or instructions before any disposal. Always wear appropriate Personal Protective Equipment. Place any paper towels from the clean-up in the trash. Remove gloves for better manipulation of the waste containers.

Check labels or instructions before any disposal. Always wear appropriate Personal Protective Equipment.

What should you do if you are using a balance that has persistent fluctuations in mass? Switch to using another balance. Record all the fluctuations as your mass reading. Contact your TA or instructor to adjust the balance. Adjust the feet on the balance yourself.

Contact your TA or instructor to adjust the balance.

Flask use

Containing a stirred reaction mixture; low accuracy

What does a GHS picture with beakers, hands, squiggly lines, and surfaces represent?

Corrosive Chemical

Meniscus

Curved surface of liquid

The pressure is kept constant, while the temperature is decreased. What will happen to the volume?

It will decrease

The volume and temperature remain constant, while some of the gas is let out of the container. What will happen to the pressure?

It will decrease

The pressure and volume are increased. What will happen to the temperature?

It will increase

The pressure and the temperature are both decreased by 50%. What will happen to the volume?

It will stay the same

Which reaction is occurring in the test tube? Clear liquid with a white, smoky-like reaction within the liquid

KCl(aq)+AgNO3(aq)⟶AgCl(s)+KNO3(aq)

What information is needed in order to be prepared for an emergency? Full inventory of all chemicals present in the lab Location of all exits Location of lab phone and first aid kit Contact information for emergency personnel Understanding of where to go should an emergency occur

Location of all exits Location of lab phone and first aid kit Contact information for emergency personnel Understanding of where to go should an emergency occur

What practice will NOT help you make an accurate volume reading on a buret at the beginning of a titration? Make sure the meniscus falls within the marked range on the buret. Make sure that the meniscus starts exactly at 0.00 mL. Read the volume at the bottom of the meniscus. Read the volume with the meniscus at eye level.

Make sure that the meniscus starts exactly at 0.00 mL.

Graduate Cylinder use

Measuring out a volume of liquid; reasonable accuracy

Waste Disposal: titrant solution

Nalgene bottle with cap

What purposes can funnels serve in the lab? Support for filter paper during a gravity filtration Assistance for pouring liquids into burets Change the speed at which a solution drips Help for transferring solid chemicals from weigh boats

Support for filter paper during a gravity filtration Assistance for pouring liquids into burets Help for transferring solid chemicals from weigh boats

Standardization

The analytical determination of the molarity of the solution

Under what conditions should a student inform the instructor of a lab injury? The instructor needs to be alerted only if he or she needs to call 911. The instructor should be alerted only if the injury involves broken skin. The instructor must be informed of all laboratory injuries. The instructor should be alerted only if the lab injury appears different from injuries the student has experienced previously.

The instructor must be informed of all laboratory injuries

In the reaction of magnesium metal with hydrochloric acid, how do you determine when the magnesium metal has reacted completely? The magnesium metal is gone. The dilute HCl is gone. Gas bubbles are no longer produced. All of the water has evaporated.

The magnesium metal is gone. Gas bubbles are no longer produced.

Equivalence/Stoichiometric point

The point at which moles of acid equals moles of base

Endpoint

The point at which the indicator changes color

Before running a titration, you calculate the expected endpoint. However, when performing the experiment, you pass the expected endpoint with no visible color change. What is the most likely problem with the titration set-up? There was an air bubble in the buret tip. The buret tip is leaking titrant into the analyte. There is not enough indicator in the analyte. The analyte solution is being stirred too quickly.

There is not enough indicator in the analyte.

Solution of known concentration that is slowly added to a solution of unknown concentration

Titrant

Process of slowly adding a solution to react with another solution and determine the concentration of one of the solutions based on the reaction between them

Titration

Precipitation reaction

Two soluble ionic compounds mixed in solution exchange ions in such a way that an insoluble ionic compound forms and precipitates out of solution

In lab, you may need to evaluate the odor or smell of a chemical. What is the best way to smell a chemical sample? Hold the sample under your nose and slowly sniff. Put your head in a fume hood as you heat the sample in it. Use your hand to gently waft the smell toward you. Vigorously shake the sample until the smell travels to you.

Use your hand to gently waft the smell toward you.

Charle's Law

V1/T1=V2/T2

Avogadro's Law

V1/n1=V2/n2

What is the main precaution to take if a Gas Cylinder sign is present in the lab? Open the valve on the gas cylinder periodically to release pressure. Visually check that the gas cylinder is restrained but keep a safe distance from it. Test out the regulator on the gas cylinder to make sure it is working properly. Remove the strap from around the gas cylinder to use it in the lab.

Visually check that the gas cylinder is restrained but keep a safe distance from it.

Liquid Waste Set-Up: C

Waste label

Soluble

When a substance dissolves in another substance

Determine when you should remove your goggles in the lab room. When everyone in the room is done handling any chemicals or glassware Whenever you need to lean in close to get a volume reading Whenever your goggles become foggy or uncomfortable When you have finished cleaning up your chemicals and glassware

When everyone in the room is done handling any chemicals or glassware

When should you start a new chemical waste container in the lab? When you accidentally spill chemicals down the side of the current container When the contents of the current container are a couple inches below the brim of the container When you need to dispose of another chemical that is compatible with chemicals in the current container When the contents of the current container completely fill the container to the brim

When the contents of the current container are a couple inches below the brim of the container

Rounding/Sig Figs: ruler

marked every 0.1 cm = record to 0.01 cm

Rounding/Sig Figs: buret

marked every 0.1 mL = read to 0.01 mL

Rounding/Sig Figs: thermometer

marked every 1 degree = record to 0.1 degree

Rounding/Sig Figs: graduated cylinder

marked every 1 mL = read to 0.1 mL

Basic Lab Techniques Equipment

metric ruler, balance, 100 mL beaker, 10 mL graduated cylinder, 100 mL graduated cylinder,

Ion Soup: cations

nitrate salts

When you need accurate measurements of chemicals, you should use ______ because ______

only glassware that has been calibrated because some volume markings are only estimates

Rounding/Sig Figs: flask

record to 0.01 mL

Rounding/Sig Figs: pipet

record to 0.01 mL

Waste Disposal: syringe tips

sharps container

When setting up your acid-base titration experiment, _____ is added to the buret and _____ is pipetted into the Erlenmeyer flask. One to two drops of _____ are added to the Erlenmeyer flask along with additional water to bring the total volume to 50 mL before beginning the titration.

sodium hydroxide, acetic acid, phenolphthalein

Ion Soup: anions

sodium salts

In the Insoluble and Soluble Salt lab, the dropper bottles containing the anions to be studied were all _____ salt solutions. The dropper bottles containing the cations to be studied were all _____ salt solutions.

sodium, nitrate

Ion Soup Equipment

spot plate, dropper bottle, various salt solutions

Ionic Equation

subscripts become coefficients

Suppose an air bubble is trapped in the eudiometer before starting the experiment. After the experiment is finished, the resulting value of R would be

too large