CHEM 208 FINAL EXAM

Beaker

An open cylindrical container with a pouring lip; used for mixing larger amounts of substances

Erlenmeyer flask

Used to hold liquids, has narrow neck to prevent splashes

Burette

Used for dispensing liquids especially during titrations

Calculate the volume of a 20.0-μg/mL Fe2+ stock solution needed to make standard Fe2+ solutions of 5.00 μg/mL, in 100 mL volumetric flasks

25 mL

What is the primary purpose of a calibration curve?

To determine the unknown concentration of an analyte in a sample by comparing its signal to a set of known standards

Identify each term in the Beer's law equation, A

Absorbance

Identify each term in the Beer's law equation, ε

Molar absorptivity

Identify each term in the Beer's law equation, b

Width of the cell

Identify each term in the Beer's law equation, C

Concentration of the samples

Beer's Law states that concentration is proportional to of light

Absorbance

According to Beer-Lambert law, when concentration of Cu2+(aq) is doubled

The absorbance doubles (2x)

Why is hydroxylamine hydrochloride added when the Fe2+ complex is made?

To ensure Fe remains in 2+ state

A sample in a spectrophotometer gives 54.5% transmittance. What is the absorbance?

0.264

Which sample absorbs the least light? (85%, 50%, 25% transmittance)

85%

Given y = 2.5x + 0.1 and absorbance = 1.6, what is concentration?

0.6

Volume of 6.0 M titrant to prepare 250 mL of 0.10 M NaOH solution

4 mL

Molarity of NaOH used to titrate 0.7154 g of KHP in 20.10 mL NaOH

0.1743

Concentration of HCl if 15 mL is neutralized by 15 mL of 0.6 M NaOH

0.6 M

Concentration of HCl if 30 mL is neutralized by 15 mL of 0.6 M NaOH

0.3 M

NaOH used in titration of 100 mL 0.2 M HCl

0.8 g

Chemical name of aspirin

Acetylsalicylic acid

Solvent used to dissolve aspirin

Ethanol

Phenolphthalein color in basic to acidic solution

Pink to colorless

At equivalence point in acid-base titration

Solution is neutral

True statement in titration

End point occurs after equivalence point

Indicator in redox titration

Potassium permanganate

Role of indicator in redox titration

Causes color change when analyte is completely reacted

True about a redox reaction

The oxidizing agent loses electrons

MnO₄⁻ is reduced to what in redox titration?

Mn²⁺

Oxidation number of Mn in MnO₄⁻

+7

Oxidation state of sulfur in H₂SO₄

+6

Element reduced in 2Fe³⁺ + 3Zn → 2Fe²⁺ + 3Zn²⁺

Iron (Fe)

Element oxidized in Zn + CuSO₄ reaction

Zinc (Zn)

H₂ is oxidized, O₂ is reduced

Redox reaction involving H₂ and O₂ forming water

Oxidation state change of nitrogen in 3H₂ + N₂ → 2NH₃

Reduced from 0 to -3

Before filling burette with titrant solution

Rinse burette with the titrant solution

Primary use of a burette

Measure volume of liquid during titrations

If air bubbles in burette

Tap to remove and fill tip with liquid

Role of potassium permanganate in redox titration

Serves as indicator due to color change

Reddish orange solution max absorbance wavelength

500 nm

Purpose of determining drug purity

Ensure correct amount of active pharmaceutical ingredient (API)

Impurity in drug analysis refers to

Any substance other than the API

Standard used for aspirin purity calibration curve

Acetylsalicylic acid

Final concentration if 500 mL of 6 M solution is diluted to 2 L

1.5 M

Final volume when 50 mL of 6 M solution is diluted to 2 M

150 mL

Volume-concentration relationship in dilution

Inversely proportional

Visible light wavelength range

400 nm to 700 nm

Purpose of blank in spectroscopy

Eliminate solvent absorption effects

Effect of too high concentration in spectroscopy

Insufficient light transmission for accurate measurement

Other CHEM208 lab using spectrophotometer

Determining iron in multivitamins

Spectrophotometer wavelength setting for lab 5

565 nm

Pathlength of cuvette used in lab

1 cm

Doubling solution concentration affects absorbance

Absorbance will double

Same mass but different volumes

Greater volume means lower density

Cutting wood block in half

Each half has same density

Mass of 100 cm³ water if density = 1 g/cm³

100 grams

How to find water mass in graduated cylinder

Subtract mass of empty cylinder from total mass

Candle floats in water but sinks in alcohol

Water is more dense than alcohol

Density difference in hot vs cold water

Molecules in hot water move faster and are further apart

mL of 2.0 M NaBr to make 200.0 mL of 0.50 M NaBr

50 mL

Molarity of diluted HCl from 2.0 mL of 6.0 M in 500 mL

0.024 M

mL of water to dilute 300 mL of 0.75 M HCl to 0.25 M

600 mL

Beer's Law equation

A = εbc

'm' in y = mx + b

Slope

εb in Beer's Law corresponds to

Slope

Color absorbed by red solution

Bluish green

Absorbance of 6.50 × 10⁻⁵ M KMnO₄ with 27.3% T, 1.15 cm, 525 nm

0.563

Calibration curve x-axis

Analyte concentration

Sum 12 + 1.2 + 0.12 + 0.012 (significant figures)

13

Correct sig figs for 1.1 × 10²

2

Chemical name of Ba(OH)₂·8H₂O

Barium hydroxide octahydrate

Grams in one mole of water

18

Moles in 90 g of water

5

Water lost heating 5.00 g BaCl₂·nH₂O to 4.26 g anhydrous

0.0411 mol

Value of n in CoCl₂·nH₂O if 1.98 g hydrate → 1.55 g anhydrous

2

Moles of HCl in 35.00 mL of 0.0919 M solution

0.00322

Phenolphthalein color in acidic to basic solution

Colorless to pink

Equivalence point in titration

Stoichiometric amount of reactant added

Molarity of NaOH if 0.5418 g KHP titrated with 25.91 mL NaOH

0.1024

Concentration of HCl if 30 mL is neutralized by 15 mL of 0.2 M NaOH

0.1 M

mmol NaOH for titrating 33 mL of 3 M HCl

100 mmol

NaOH used in titrating 100 mL of 0.1 N HCl

0.4 g

Percent by mass of 20.0 g NaCl in 180.0 g water

10.0%

Chemical change vs physical change

Chemical change forms new substance; physical change does not

In a chemical reaction

Atoms unbond, rearrange, and rebond to form products

Mass conservation in reaction

Mass of reactants = mass of products

Molecule count in chemical equation shown by

Coefficient

Number of oxygen atoms in 2Ca(NO₃)₂

12

Allowed step when balancing chemical equations

Write coefficients

Precipitate forms when

Two liquids react and a solid forms