Chem 123L Final (6 labs, 22 mc & 3 questions from each lab)

Suppose you are performing a titration. At the beginning of the titration, you read the titrant volume as 2.94 mL. After running the titration and reaching the endpoint, you read the titrant volume as 16.47 mL. What volume, in mL, of titrant was required for the titration?

13.53 To find the volume of titrant used in any titration, subtract the starting volume reading from the final volume reading.

What is a direct relationship in chemistry?

A direct relationship is when one variable increases, so does the other.

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 19.6 mL solution of the vinegar?

0.0224 First, determine the mass of acetic acid in the sample from the volume and the described content. Then, divide by the molar mass of acetic acid to find the moles present. moles=19.6 mL×0.0685 g1 mL×1 mol60.052 g

What is the value of the gas constant, R, in units of L⋅atmmol⋅KL⋅atmmol⋅K ? Report the value with at least three significant figures.

0.0821

R value for this experiment

0.0821 L*atm/mol*K

The molar absorptivity of a compound at 500 nm wavelength is 252 M-1cm-1. Suppose one prepares a solution by dissolving 0.00140 moles of a solute in enough water to make a 500.0 mL solution. What would be the absorbance in a 3 .00 mm pathlength cell?

0.212

Sugar is easily soluble in water and has a molar mass of 342.30 g/mol. What is the molar concentration of a 235.2 mL aqueous solution prepared with 75.2 g of sugar?

0.934

Determine the oxidizing agent in the following reaction. Ni(s) + 2 AgClO4(aq) -> Ni(ClO4)2(aq) + 2 Ag(s)

Ag

Hydrochloric acid, HCl, is corrosive and a strong irritant. What measures should be taken when working with this material?

Always wear safety goggles when handling this chemical. Always wear gloves when handling this chemical.

relationship between temperature and pressure

As the temperature of a gas increases, the pressure it exerts on its container will increase.

Consider an experiment in which pressure and temperature are held constant and gas is being collected.What relationship exists between the moles of gas and the collected volume of gas?

As volume of gas increases, the number of moles is increasing.

Determine when to put on disposable gloves for work in the lab.

Before handling any glassware or chemicals for the experiment.

When using a pH meter to monitor a stirring reaction mixture, where should you place the pH sensor electrode?

Between the stirring vortex and the side of the glasswar

Mass/Pressure Relationship

Boyle's law states that at constant temperature the volume of a given mass of a dry gas is inversely proportional to its pressure.

Read each statement regarding food and beverages in the lab and determine if each is true or false.

Chewing gum is okay in the lab as long as you don't blow bubbles = False Tobacco products of all kinds are prohibited in lab = True Food items should not be brought into the lab = True Beverages are allowed in lab as long as they are in containers with lids = False

What is the correct net ionic equation to describe this precipitation reaction? Co(NO3)2(aq)+2NaOH(aq)⟶2NaNO3(aq)+Co(OH)2(s)

Co2+(aq)+2OH−(aq)⟶Co(OH)2(s)

A student completes her titration and determines the volume of NaOH needed to reach the endpoint of the titration. Her data is shown below. Taking outliers into account, should all four trials be used in the average calculation in each data set? Data Set 1 Trial 1 23.11 mL Trial 2 23.20 mL Trial 3 21.22 mL Trial 4 23.17 mL Data Set 2 Trial 1 46.44 mL. Trial 2 46.24 mL Trial 3 46.20 mL Trial 4 46.39 mL

Data set 1: no trial 3 Data set 2: all are close

How to calculate the enthalpy of a reaction?

Enthalpy of a Reaction, kJ mol = heat lost by reactants / moles reacted

Ideal Gas Law & pv=nRt

Exploration of the Ideal Gas Law- Review the experimental set-up for each part of the experiment. Can you identify how unchanging variables were held constant using given lab equipment? Can you rearrange the Ideal Gas Law and identify a direct or indirect (inverse) relationship in the Ideal Gas Law? Do you know how to calculate absolute zero from the graph produced in the experiment? And calculate percent error from the known value?v

Endpoint and equivalence point mean the same thing.

FALSE The endpoint and the equivalence point should happen at the same time, but they are not the same thing. The endpoint is the at point at which a color change occurs in the system. The equivalence point is the at point at which the chemical reaction is complete.

Determine which items of personal protective equipment (PPE) you will likely use in a general chemistry lab.

Gloves, Goggles, & Labcoat

What is the net ionic equation for the reaction between HCl and NaOH?

H+ + OH− ⟶ H2O

Identify the predicted color of a universal indicator when added to solutions of different pH conditions. Weakly basic solution with a slightly high pH Strongly basic solution with a very high pH Weak acid solution with a slightly low pH Neutral solution with a pH around 7 Strong acid solution with a very low pH

Weakly basic solution with a slightly high pH =Blue Strongly basic solution with a very high pH =Violet Weak acid solution with a slightly low pH =Orange or yellow Neutral solution with a pH around 7 =Green Strong acid solution with a very low pH =Red

Determine the safest option in the lab if you need your vision to be corrected.

Wear corrective glasses or lenses under your safety goggles for the whole experiment, but always check with your TA or Instructor for your school's policy.

When describing the uncertainty of a measurement, the term __________ refers to the closeness between a measurement and its accepted value, whereas the term __________ refers to the closeness among a set of measurements.

When describing the uncertainty of a measurement, the term accuracy refers to the closeness between a measurement and its accepted value, whereas the term precision refers to the closeness among a set of measurements.

Determine when you should remove your goggles in the lab room.

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

Identify two issues that can arise when measuring heat changes for a chemical reaction using a calorimeter

Heat can be lost to the calorimeter over time, which is particularly an issue for reactions that proceed slowly. Heat can come from the reaction of interest as well as any side reactions.

What occurs in endothermic reactions?

Heat energy is absorbed.

When exothermic reactions occurs

Heat energy is released.

In Part 1 of this experiment, the relationship between pressure and temperature of a gas is examined. How will the temperature be changed in the experiment?

Heating it in a water bath.

Indicate the oxidation number of iodines in the following ions. IO˜ IO2- IO3-

IO˜ = +1 IO2- = +3 IO3- = +5

In the experiment Stoichiometry: A Spectrophotometric Study, nine solutions containing a complex ion will be made. The source for the metal cation is _________ and the ligand with either be ___________ or______________.

In the experiment Stoichiometry: A Spectrophotometric Study, nine solutions containing a complex ion will be made. The source for the metal cation is copper (II) sulfate pentahydrate and the ligand with either be ethylenediamine or tetraethylenepentamine.

LEO goes GER

Looses elections = oxidation Gains elections = reduction

Molar mass formula

M=m/n M = molar mass m = mass of a substance (in grams) n= number of moles of a substance

In the reaction Mg + 2HCl → MgCl2 + H2 Mg is _________ and H is __________

Mg is oxidized H is reduced

How many moles of H2 can be formed if a 2.97 g sample of Mg reacts with excess HCl?

Mg+2HCl⟶MgCl2+H2 Mg reacts with HCl to form H2 as shown. There is a 1:1 ratio between the Mg & H2, convert the given mass of Mg to moles, this will also give the moles of H2. solution=0.122

Identify the color absorbed by a solution that should appear as the given color: Orange Blue Red Green

Orange = Blue Blue = Orange Red = Green Green = Red

Which is an example of an accurate manipulation of the Ideal Gas Law?

PV=(nT)/R (PV)/R=nT PV=(nR)/T PV=(RT)/n

percent error equation

Percent Error = (e-t)/t x 100

Which method should be used when stirring the contents of the calorimeter?

Place a stir bar in the calorimeter

What is generally the best approach when liquid from a large reagent bottle is needed in an experiment?

Pour some of the reagent from the bottle into a beaker, then use as needed in the procedure.

Calculate total mass of the solution based on the physical state of the reactants. Mass will have 3 significant figures based on the density of water in the equation.

Reaction 1 (mass NaOH solid, g) + (volume of water, mL)(1.00 g mL) = Total mass Reaction 2 (volume NaOH, mL)(1.00 g mL) + (volume of HCl, mL)(1.00 g mL) = Total mass Reaction 3 (mass NaOH solid, g) + (volume of HCl, mL)(1.00 g mL) + (volume of water, mL)(1.00 g mL) = Total mass

What should you do every time before you leave the lab?

Remove your gloves. Remove your lab coat, if you are wearing one. Wash your hands.

What is heat energy transferred at a constant pressure called?

The enthalpy of a reaction

what is the difference between experimental and theoretical values?

The experimental value is your calculated value, and the actual value is the known value.

Under what conditions should a student inform the instructor of a lab injury?

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? Select all that apply: Mg(s)+2H+(aq) →Mg2+(aq)+H2(g)

The magnesium metal is gone. Gas bubbles are no longer produced. The magnesium metal and the hydrochloric acid react to produce hydrogen gas. The magnesium is completely reacted when no more bubbles are formed and the magnesium metal is gone.

what is the stoichiometric point/equivalence point?

The point at which the acid has been exactly neutralized by the base is called the equivalence point, or the stoichiometric point The equivalence point is the point at which moles of acid equals moles of base.

what is the titrant in this experiment?

base (NaOH)

Determine where to dispose of each type of waste.

broken flask = Box lined with puncture resistant bag titrant solution = Nalgene bottle with cap unused solid reagent = Solid waste container syringe tips = Sharps container

When setting up the experiment, the temperature sensor should be plugged into _______________of the Vernier interface and the gas pressure should be plugged into ___________________

ch 2 ch 1

Identify the items needed to run a spectrophotometry experiment.

cuvette spectrophotometer sample solutions blank solution

Calculate the enthalpy change (in kJ/mol) for the combustion of CS2 (l) using the enthalpy values given in the table. CS2(l)+3O2(g)⟶CO2(g)+2SO2(g) C(s)+O2(g)⟶CO2(g)C(s)+OX2(g)⟶COX2(g). ^H= −393.6 S(s)+O2(g)⟶SO2(g)S(s)+OX2(g)⟶SOX2(g) ^H= −296.8 C(s)+2S(s)⟶CS2(l)C(s)+2S(s)⟶CSX2(l) ^H= +87.9

-1075.1 kJ/mol

Calculate the enthalpy change (in kJ/mol) for the combustion of CS2(l)+3O2(g)⟶CO2(g)+2SO2(g) using the enthalpy values given in the table. Reaction ΔHΔH in kJ/molC(s)+O2(g)⟶CO2(g)C(s)+OX2(g)⟶COX2(g)−393.6−393.6S(s)+O2(g)⟶SO2(g)S(s)+OX2(g)⟶SOX2(g)−296.8−296.8C(s)+2S(s)⟶CS2(l)C(s)+2S(s)⟶CSX2(l)+87.9

-1075.1 kJ/mol

What are the best practices for safely handling waste in the lab?

1.) Check labels or instructions before any disposal. 2.) Always wear appropriate Personal Protective Equipment.

To calculate the pressure of the hydrogen gas produced by the reaction of magnesium metal and hydrochloric acid, students will use ______________. To determine the number of moles of hydrogen gas collected, students will use _______________.

1.) Dalton's Law of Partial Pressure 2.) The Ideal Gas Law

The heat energy absorbed or released during a chemical reaction is known as _______________ , or ΔH. A reaction that is exothermic, or releasing energy, will have a ΔH value that is ______________. A reaction that is endothermic, or absorbing energy, will have a ΔH value that is ________________.

1.) enthalpy 2.) negative 3.) positive

Identify the equipment best suited for extinguishing each type of fire. clothing fire: large fire on floor: small bench top fire:

1.) fire blanket 2.) fire extinguisher 3.) overturned beaker

In the Determination of the Molar Mass of Magnesium lab, how is the temperature of the hydrogen gas determined?

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

What is Hess's Law?

The total enthalpy change of a reaction is independent of the route taken.

Aluminum oxide also reacts with hydrochloric acid through the following reaction. Al2O3(s)+6HCl(aq)⟶2AlCl3(aq)+3H2O(l) Is this an oxidation-reduction reaction???

This is not an oxidation-reduction reaction because no electrons are transferred.

how to condition buret?

To condition the buret, add a small volume of the titrant to the buret and rotate the barrel at an angle close to horizontal so that the liquid makes contact with the full inner surface of the barrel. Complete this action two more times and discard each volume in a designated waste container.

Why should you always condition a buret before running a titration?

To ensure there is no dilution from water that remains from cleaning

Identify the first step in preparing a spectrophotometer for use.

Turn on the light source and the spectrophotometer.

Titration Terms

When the required amount of one solution has been added to the second solution to complete the reaction =Endpoint A reagent added to the analyte solution that changes color when the reaction is complete =Indicator Process of slowly adding a solution to react with another solution and determine the concentration of one of the =Titration Solution of an unknown concentration that has another solution slowly added to it =Analyte Solution of known concentration that is slowly added to a solution of unknown concentration =Titrant Glassware that allows a solution to be precisely and slowly added to another solution =Buret

Match each lab incident to the item of PPE that will protect you from it.

While picking up a buret, an unknown solution left by a previous solution drips onto your hand. =Gloves While pulling an empty beaker off the shelf at the beginning of lab, it slips out of your hand onto the floor. =Closed-toe shoes While checking on a stirring solution, the solution splashes up towards your face. =Goggles While transferring a solution from a flask to a beaker, the solution accidentally spills down the front of the lab bench. =Lab coat

What does PVnRT stand for?

𝑃 =pressure, atm 𝑉 = volume (L) 𝑛 =number of moles 𝑇 =temperature, K R = gas constant, 0.0821 L⋅atm/mol⋅K

molar ratio (stoichiometric factor)

moles of required / moles of given

When taking a measurement with a pH meter, keep the instrument in the storage solution until it is needed. Rinse the pH meter with deionized water and gently pat dry. Place the meter in the sample solution, and record the measurement when the pH stabilizes.

n/a

what is the analyte/aliquot in this experiment?

the acid solution, which is measured in a precise amount to ensure quality results

Suppose an air bubble is trapped in the gas buret before starting the experiment. After the experiment is finished, the resulting value of the volume of hydrogen gas would be

too large

when is the endpoint of a titration?

when the color changes

Suppose you have 200.0 mL of a 0.750 M sodium hydroxide solution. How many moles of sodium hydroxide are in the solution?

0.15 The definition of molarity is Molarity=moles of soluteliters of solutionMolarity=moles of soluteliters of solution Because you know the molarity and volume of the solution, you can calculate the moles of sodium hydroxide, NaOH, solute. First, convert milliliters to liters using the definition of the metric prefix. volume in liters=200.0 mL solution×1 L1000 mLvolume in liters=200.0 mL solution×1 L1000 mL Then, multiply the volume by the molarity to find moles of NaOH. moles of NaOH=volume in liters×0.750 mol1 Lmoles of NaOH=volume in liters×0.750 mol1 L

Suppose you have 350.0 mL of a 0.450 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 concentration, with a sodium hydroxide solution according to the equation: HC2H3O2 + NaOH ->H2O + NaC2H3O2 If you require 33.81 mL of 0.1943 M NaOH solution to titrate 10.0 mL of HC2H3O2 solution, what is the molar concentration of acetic acid in the vinegar?

0.657

If you drop or break glassware in lab, first ______________________ . Then, ____________________________________. Finally, place all that material into the _________________________.

1.) get thick gloves or dustpan 2.) carefully collect all the broken glassware 3.) broken glass container

A calorimeter measures the ___________ involved in reactions or other processes by measuring the ________________ of the materials _______________ to prevent transfer of heat to outside the device. The calorimeter is _____________ to prevent transfer of heat to outside the device.

1.) heat 2.) temperature change 3.) surrounding 4.) insulated

The temperature of a room is 19.1 °C. What is this temperature expressed in Kelvin (K)?

19.1∘C+273.15 = 292.3

The temperature of a room is 21.4 °C. What is this temperature expressed in Kelvin (K)?

294.6

In Part 3 of the experiment Exploration of the Ideal Gas Law, where the relationship between pressure and moles of a gas is investigated, a 2-liter bottle is pressurized. What is the recommended pressure for this part of the experiment?

40-50 psi explanation: The recommended pressure for this part of the experiment is 40-50 psi.

A titration curve is a plot of ___________on the x-axis and __________ on the y-axis.

A titration curve is a plot of titrant volume on the x-axis and pH on the y-axis.

spec terms

A unit commonly used in spectrophotometry that is inversely proportional to energy and commonly measured in nanometers double_arrowWavelength A sample prepared using the solvent and any other chemicals in the sample solutions, but not the absorbing substance double_arrowBlank A square-shaped container, typically made of quartz, designed to hold samples in a spectrophotometer double_arrowCuvette A measurement of the amount of light that passes through a sample double_arrowTransmittance A measurement of the amount of light taken in by a sample double_arrowAbsorbance

What type of plot can be used to determine λ max of a solution?

Absorbance vs. wavelength

pressure and volume relationship

Boyle's law is a gas law, stating that the pressure and volume of a gas have an inverse relationship. If volume increases, then pressure decreases and vice versa, when the temperature is held constant.

How to change gloves in lab setting.

Changing gloves often will minimize the spread of chemicals. To properly remove gloves, first, grasp the exterior of one glove with a gloved hand, and then, peel off the first glove . Then insert a bare finger between the interior edge of the second glove and the skin, and remove the second glove.

A student removes a chemical sample from a reagent bottle to be used in an experiment. What should be done with any excess chemical remaining from this sample after the experiment is complete?

Check and see if anyone else can use the chemical. If not, discard in the proper waste container.

what is an inverse relationship in chemistry?

Inverse relationships, or negative relationships, are between two variables that have a negative correlation. When one variable increases, the other decreases, and vice versa.

What information is needed in order to be prepared for an emergency?

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

Suppose 0.0350 g Mg is reacted with 10.00 mL of 6 M HCl to produce aqueous magnesium chloride and hydrogen gas. What is the limiting reactant in this reaction? 2Mg + 2HCl → MgCl2 + H2

Magnesium metal

According to the experimental procedure, which method will be used to mix the analyte solution while titrating?

Magnetic stir bar

matching

Small ion or compound acting as a Lewis base =Ligand Ligand that makes more than one bond with a metal cation =Chelate Product of the reaction of a metal cation and a ligand =Coordination complex Ratio of ligand to cation in a coordination complex = Stoichiometry

relationship between absorbance of light by a solution and its concentration

The relationship between absorbance of light by a solution and its concentration should be linear so that when concentration increases, absorbance increases.

Setup of spectrophotometry experiment

To run a spectrophotometry experiment, begin by warming up the spectrophotometer and preparing the samples. Be sure to select the correct wavelength, then run a measurement on the blank solution. Follow up by running measurements on sample solutions. Once data is collected, turn off the instrument, clean the area, and discard the samples.

1. During a demonstration, a chemistry professor took an empty 5.0 L metal can, heated it with the lid off, sealed it while hot then threw it into a bucket of ice water. With a loud bang, the can collapsed. (2/2pts) If the 5.0 L can was initially heated to 82.2 °C and the temperature of the can was lowered to 2.0 °C in the ice bath, what was the final volume of the can once it collapsed? Hint: This is an application of Charles Law.

V2=(5.0L)(273.15+2 K)/(273.15+82.2) K = 3.9 L

When filling a buret

When filling a buret for a titration, first adjust the buret in the clamp so that the opening is near eye level. Then, use a funnel to add the titrant into the buret. The titrant should be filled almost to the zero mark.

How to set up this titration>>>>>>>

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

Parts 1 and 3 of the experiment capture a volume of gas in syringes. In Part 1, a _____________ syringe is used, whereas in Part 3 a ______________ syringe is attached to the pressure sensor.

a.) 30 ml b.) 20 ml

Iron metal can be oxidized by strong acids as shown in the following reaction. Fe(s)+2HCl(aq)⟶H2(g)+FeCl2(aq) What is the net ionic equation??? What chemical species is reduced??? How many electrons are transferred during the reaction?

a.) Fe(s) + 2H+(aq) → H2(g) + Fe2+(aq) b.) H+ c.) 2

A balloon is inflated outside on a cool morning. As the temperature rises, reaching its peak in the afternoon, the volume of the balloon will ______________. As the temperature cools down again in the evening, the volume of the balloon will ________________.

a.) increase b.) decrease

Dalton's Law of Partial Pressures states that the total pressure of a gas mixture is equal to the _______ of the ____________________________ as long as _________________________.

a.) sum b.) partial pressures of all gas components c.) the gases do not react with one another

Identify the safety equipment designed to deal with each emergency listed.

chemicals in eyes ->eyewash station cuts or minor burns -> first aid kit large fire on the bench top -> fire extinguisher fire on a person -> fire blanket chemicals on clothes -> safety shower

If the temperature of reaction decreases then it is a ______ reaction.

endothermic the enthalpy of the reaction > zero

If the temperature of a reaction decreases then it is a _____ reaction.

exothermic the enthalpy of the reaction < zero

determine the every way to fix each of the problems with this lab student

flowy sleeves ->Tie back or secure loose bracelets ->Remove long hair -> Tie back or secure long necklaces -> Remove long earrings -> Remove