Chem 102 Pre-Lab Quiz (Equilibrium, Titration: Standardization of a NaOH Solution, Titration: Identification of an Unknown Acid)

The main objectives for Experiment EQB and its in/post-lab assignment are (select all that apply):

Select one or more:

Use Beer's Law to calculate the wavelength needed for spectrophotometry

Determine the equilibrium constant for the reaction of NaSCN and Fe(NO3)3 to form [Fe(NCS)]2+

Determine the relationship between the concentration of [Fe(NCS)]2+ and the absorbance to find this analyte's molar absorption coefficient

Convert the absorbance measurements from equilibrium samples to concentrations of the product at equilibrium

Find the rate of the reaction between NaSCN and Fe(NO3)3

Determine the equilibrium constant for the reaction of NaSCN and Fe(NO3)3 to form [Fe(NCS)]2+

Determine the relationship between the concentration of [Fe(NCS)]2+ and the absorbance to find this analyte's molar absorption coefficient

Convert the absorbance measurements from equilibrium samples to concentrations of the product at equilibrium

What physical property of which compound are you monitoring?

Select one:

The UV/Visible absorption of the reactant, Fe(NO3)3

The pKa of reactant, Fe(NO3)3

The UV/Visible absorption of the reactant, NaSCN

The UV/Visible absorption of the product, [Fe(NCS)]2+

The UV/Visible absorption of the product, [Fe(NCS)]2+

Le Chatelier's Principle states that:

Select one:

as a reaction reaches equilibrium, the K values increase

a chemical reaction will always restore equilibrium when perturbed

as temperature increases, the pH of a reaction also increases

a chemical reaction will spontaneously go to completion if enough energy is put into the system

a chemical reaction will always restore equilibrium when perturbed

The equilibrium below is the reaction of interest.

Fe^3+ + SCN^- <> [Fe(NCS)]^2+

In the preparation of the standard solutions, which reactant will be used in excess?

[Fe(NCS)]2+

NaSCN

Fe(NO3)3

Which reactant will essentially be converted entirely to product?

Fe(NO3)3

NaSCN

[Fe(NCS)]2+

Fe(NO3)3

NaSCN

Temperature is NOT a factor we will be considering this class period. However, the reaction in question is an exothermic reaction. Select all of the following conditions that could perturb the reaction to proceed in the forward direction.

Select one or more:

adding more reactant

adding more heat

adding an inert gas

adding more product

removing heat

adding more reactant

removing heat

A volumetric flask has the following characteristics (select all that apply):

Select one or more:

Glassware that is designed to stand harsh conditions like extreme heat and cold

Has a flat base

Can have a metal joint stopper

Has a tare mark in the neck for the exact volume

When swirling the flask to mix a solution, only the neck must be supported

Can have a plastic joint stopper

Glassware that can give volumes 3 to 4 significant figures

Can have a glass joint stopper

Has a flat base

Has a tare mark in the neck for the exact volume

Can have a plastic joint stopper

Glassware that can give volumes 3 to 4 significant figures

Can have a glass joint stopper

Select all equipment items below that you will use in some capacity during the EQB lab.

Select one or more:

Cuvettes

Micropipette tips

Scintillation vials

Beaker

Micropipettes

Glass pipettes

Plastic transfer pipettes

Erlenmeyer flask

10-mL volumetric flask with a yellow plastic cap

Cuvettes

Micropipette tips

Scintillation vials

Beaker

Micropipettes

Plastic transfer pipettes

10-mL volumetric flask with a yellow plastic cap

Solve the following question using the information given in the image below. If applying Beer's law, use the y=mx+b form of Beer's Law and assume l = 1.000 cm.

What is the Equilibrium Concentration (M) of iron thiocyanate in this reaction given the values provided?

1.00 x 10-3 M

2.00 x 10-3 M

6.00 x 10-3 M

9.21 x 10-5 M

Other

9.21 x 10-5 M

What do chemical equilibrium constants tell us about the reaction?

Select one:

The extent to which a reaction occurs

The standardization of a desired solution

The amount of moles needed to create a product

The effect of temperature on the reaction

The extent to which a reaction occurs

True or false: 1.00 molar nitric acid, not deionized water, will be used when preparing the Fe(NO3)3 stock solution, preparing the blank cuvette sample, and diluting all standard/equilibrium cuvette samples.

Select one:

False

True

True

The main purpose for the AB1: Standardization of NaOH experiment is to:

Select one:

Determine the volume needed to titrate an unknown acid

Determine the necessary volume needed to make 0.1 M NaOH

Titrate a sodium hydroxide (NaOH) solution of unknown concentration with potassium hydrogen phthalate (or KHP-the primary standard) to determine the true concentration of the NaOH (the secondary standard).

Learn about safety

Navigate through the procedure and make no mistakes

Titrate a sodium hydroxide (NaOH) solution of unknown concentration with potassium hydrogen phthalate (or KHP-the primary standard) to determine the true concentration of the NaOH (the secondary standard).

In this lab, we will be measuring:

Select one:

pH as a function of volts

pH as a function of volume

pH as a function of color

pH as a function of time

pH as a function of volume

The following items will be part of the experimental setup as you collect data over the course of the lab. Select all that apply.

Select one or more:

Kim wipe

Vernier pH probe

Burette clamp

Stir bar

Stir plate

Beaker or flask containing dissolved KHP

Vernier Temperature probe

Burette

Hot plate

Vernier Graphical Analysis

Vernier Conductivity probe

Phenolphthalein

Kim wipe

Vernier pH probe

Burette clamp

Stir bar

Stir plate

Beaker or flask containing dissolved KHP

Burette

Vernier Graphical Analysis

Phenolphthalein

During lab, you will use the dilution equation

Choose...M₁V₁=M₂V₂/pH=-log(H⁺) when preparing your Choose...0.1/1.0 check_circle_outline M solution of NaOH

M₁V₁=M₂V₂

0.1

In the colorimetric titration experiment, we expect the indicator, Choose...phenolphthalein/KHP/unknown acid to change from Choose...pink/colorless in acidic solutions to Choose...pink/colorless

check_circle_outline in basic conditions.

phenolphthalein

colorless

pink

The following characteristics define what a primary standard is. Select all that apply.

Select one or more:

Soluble in water

Dries readily

Reacts only partially to the substance being standardized

Insoluble in water

Has a detectable equivalence point with high accuracy

Stable in air

Doesn't have an equivalence point

Low in purity

Unstable in air

Has quantitative reactivity with the substance to be standardized

High in purity

Soluble in water

Dries readily

Has a detectable equivalence point with high accuracy

Stable in air

Has quantitative reactivity with the substance to be standardized

High in purity

You prepare a solution by dissolving 0.743 g potassium hydrogen phthalate (KHP, 204.221 g/mol) in 25.0 mL of distilled deionized water with 2 drops of phenolphthalein. It takes an addition of 17.33 mL approximately 0.1 M sodium hydroxide (NaOH) stock solution to turn your KHP solution a faint shade of pink. What is the true concentration of [OH-] in your prepared NaOH stock solution?

Select one:

0.0860 M

0.210 M

0.00210 M

0.210 M

How can a titration curve be defined?

Select one:

It is a graphical description of the solution pH as a function of the volume of added titrant.

It shows the starting pH of a solution and what happens over time upon heating.

It is a graphical description of the solution color change as the conjugate ion of the indicator is formed.

It is used to calculate with more accuracy the equivalence point volume of the titration.

It is a plot that shows only the addition of titrant into a solution over time.

It is a graphical description of the solution pH as a function of the volume of added titrant.

Select all that apply: According to the background reading, our analysis will entail

Select one or more:

A titration curve

A spectrum of the absorption of phenolphthalein

A plot of temperature of solution over time

A first derivative plot to confirm the point where moles of acid = moles of base

A titration curve

A first derivative plot to confirm the point where moles of acid = moles of base

The inflection point is the greatest change in slope along the acid/base titration curve. The first derivative plot peak:

Select one:

corresponds to the region of greatest slope, therefore an equivalence point in the titration curve.

corresponds to the amount of titrant added to the titration.

corresponds to the volume needed to reach a pH of 7.

corresponds to the starting pH of the solution.

corresponds to the region of greatest slope, therefore an equivalence point in the titration curve.

Acids may have several equivalence points due to the presence of multiple protons.

Select one:

True

False

True

The proper method to load a burette with solution is:

Select one:

without gloves so one can have a better grip

at eye level (lowering the burette in the sink or acquiring a stool as necessary)

on the bench top over the head

at eye level (lowering the burette in the sink or acquiring a stool as necessary)

You will store your left-over prepared secondary standard, the NaOH stock solution, for next week's lab: AB2 Identification of an unknown acid.

Select one:

True

False

True

Important PPE for this lab includes (select all that apply):

Select one or more:

Masks

Gloves (to be worn at all times even on a computer)

Lab coat (to be worn buttoned at all times in the lab space)

Gloves (to be worn at all times manipulating the experimental set-up)

Goggles (to be worn over eyes at all times in the lab space)

Close toed shoes fully enclosing feet, with no open back/top or vent holes

Lab coat (to be worn buttoned at all times in the lab space)

Gloves (to be worn at all times manipulating the experimental set-up)

Goggles (to be worn over eyes at all times in the lab space)

Close toed shoes fully enclosing feet, with no open back/top or vent holes

The main purpose for the AB2 experiment is to:

Select one:

determine the equilibrium constant for the titration

determine the pKa(s) of an unknown acid and thus identify the unknown titrated

confirm the concentration of sodium hydroxide from AB1

determine the time it takes for the equivalence point to be reached

determine the pKa(s) of an unknown acid and thus identify the unknown titrated

It is important to have proper technique in addition of the titrant to:

Select one:

ensure only parts of the solution are being neutralized.

proper technique is not necessary.

ensure the reaction is making only products.

ensure all equivalence points can be observed.

ensure all equivalence points can be observed.

Why is it important to condition the burette?

Select one:

To minimize the amount of base that can be added to the buret.

To ensure that the solution will be stirring on a stir plate

To determine the volume needed for the titration.

To ensure that all of the residual impurities are removed.

To ensure that all of the residual impurities are removed.

For this experiment, we are running a neutralization reaction. The titrant is Choose...water/sodium hydroxide and it goes in the buret; the unknown acid goes in the Choose...vial/beaker/polyethylene bottle with a stir bar.

sodium hydroxide

beaker

Why are bubbles in the burette bad?

Select one:

It's a sign the titration is finished; they are not bad.

The bubbles stem from using too strong of titrant so new solution must be prepared.

It adds unnecessary error, distorting the buret volume reading

It adds unnecessary error, distorting the buret volume reading

If 0.119 g of an unknown diprotic acid is being titrated with 16.0 mL of a standardized concentration of the NaOH solution (0.107 M). What is the molar mass of the unknown acid?

Select one:

25 g/mol

139 g/mol

70 g/mol

139 g/mol

What does having an unstandardized solution of sodium hydroxide (NaOH) mean?

Select one:

The temperature of the solution is too high to be used.

The solution will likely react with moisture in the air.

The base is not equally distributed in the solution so it needs to be stirred more.

The exact concentration has not been determined.

The exact concentration has not been determined.

To store the pH probe, you should ensure that it is plugged in to charge upright and confirm that the tip is immersed in distilled water within its storage container.

Select one:

True

False

False

Consider this process: A student weighed out KHP using the weigh-by-difference technique. They performed steps in this order: 1) weighed the KHP vial, 2) removed the cap, 3) added a small amount of KHP to the Erlenmeyer flask, 4) re-weighed the vial, and 5) recapped the vial to put it away.

The student correctly performed the technique.

Select one:

True

False

False