Chem 01LA Quizzes

In the previous experiment, you obtained the density by dispensing 25.00 mL of water from. a pipet into a weighed flask, then re-weighing the flask after the addition of water. How would your density result compare to the true density if (unknown to you) a small amount of residue from the lab bench adhered to the outside of the flask just before you re-weighed it? Assume the flask was clean and dry before the initial weighing. Choose your answer and explain. a. It does not affect the result b. It will be larger than the true density c. It will be smaller than the true density d. More information is needed

b. It will be larger than the true density : if there was a small amount of residue left over before re-weighing, then the density will be larger than the true density bc now there's more mass that wasn't accounted for greater mass = greater density

Match each of the following terms with its definition by placing the corresponding letter in the space provided. a.) carbohydrate b.) deliquescence c.) efflorescence d.) desiccant _____ An anhydrous compound that will absorb water from the air or other source. _____ An example of a substance that is not a true hydrate. _____ When a hydrate loses water upon standing. _____ When a substance takes up so much water from the atmosphere that it dissolves.

d - desiccant a - carbohydrate c - efflorescence b - deliquescence

Rank the following photons from lowest to highest energy (left to right). a.) visible (λ = 650 nm) b.) infrared (λ = 10^-5 m) c.) ultraviolet (λ = 10^-8 m)

infrared < visible < ultraviolet

Briefly describe how you will determine the interior volume of the 25 mL flask in today's experiment.

measuring the volume displaced using water, volume can be determined for any solid fill flask w water, add metal, record change in volume

Fill in the blank: The ______ is the curved surface that appears at the top of a liquid in a container (such as a buret or a pipet).

meniscus

How many decimal places should the volume of liquid in a buret be recorded?

one hundredth : 0.01

Give a brief definition of density

the amount of mass per given volume/space

Rank the following photons from highest to lowest energy (left to right). a.) visible (λ = 650 nm) b.) infrared (λ = 10^-5 m) c.) ultraviolet (λ = 10^-8 m)

ultraviolet > visible > infrared

Briefly describe how you will determine the density of water using a 25 mL volumetric pipet and a 25 mL flask.

weigh the flask ; pipet in 25 mL of water into the flask ; measure the weight of the flask again ; calculate for mass of water ; divide the mass of water by volume

One of the lines in the Balmer series of the hydrogen atom emission spectrum occurs in the UV region at 384 nm. It results from a transition from an upper energy level to n = 2. What is the principal quantum number of the upper energy level? Rydberg constant = 1.097 x 10^7 m^-1 1/λ = RH (1/nl^2 - 1/nh^2) a. nh = 9 b. nh =7 c. nh = 5 d. nh =3 e. none of the above

x = 3.8357 x 10^-7 ~ 384 nm nh = 9

Mass of empty flask + stopper = 54.232g Mass of flask + stopper + H2O = 153.617g Mass of flask + stopper + metal = 143.557g Mass of flask + stopper + metal + H2O = 226.196g Density of H2O = 1.00 g/mL How do you report the density of metal ?

1) Get mass of H2O : ( mass of stoppered flask + water) - (mass of empty flash + stopper) 2) Find internal volume of flask/the volume of water : (m of H2O/density of H2O) cm^3 3) Find mass of surrounding H2O : (m of flask + stopper + metal + H2O) - (m of flask + stopper) - (mass of metal) 4) Find volume of H2O surrounding the metal : (m of H2O/density) cm^3 5) Find the volume of the metal : (internal volume of flask) - (volume of H2O surrounding the metal) 6) Find the density of the metal (D = m/v)

A piece of copper with a mass of 20.48 g is submerged in 46.3 cm^3 of water in a graduated cylinder. The water level increases to 48.6 cm^3. Report the density of copper to the proper number of significant figures.

8.904 g/cm^3

A piece of bismuth with a mass of 22.54 g is submerged in 46.3 cm^3 of water in a graduated cylinder. The water level increases to 48.6 cm^3. Report the density of bismuth to the proper number of significant figures.

9.8 g/cm^3

What is the formal charge on the middle nitrogen in :..N..---N⏚O: ? Include the sign (+ or -) and show your calculation.

:..N..---N⏚O: 2- + + N = 5 O = 6 5-7 = -2 5-4 = +1 6-5 = +1

Write the mathematical equation for Beer's Law and briefly explain each symbol in the expression.

A = εbC A = absorption of solution ε = molarity b = path length of the solution C = concentration

When blue copper (II) sulfate pentahydrate is heated, it completely loses the water of hydration and forms a white solid. How many moles of water are lost when 0.0456 mole of copper (II) sulfate pentahydrate is heated? (MM Cu = 63.55 g/mol ; MM S = 32.07 g/mol ; MM O = 16.00 g/mol ; MM H = 1.008 g/mol)

CuSO4 (5H2O) 63.55 + 32.07 + 5(16.00 + 2.016) 0.228 moles

Complete the following Lewis structures for the NCS- ions by adding nonbonding electrons (lone pairs). Indicate the formal charge beneath each atom. Circle the more stable structure and explain why it is preferred. (Electronegativity values : C = 2.5 ; N = 3.0 ; S = 2.5) [ N ⏚ C -- S ] ‾ [ N == C == S ] ‾

[ : N ⏚ C -- S..:.. ] ‾ 0 0 -1 5 - 4/2 - 4 = -1 [ : : N == C == S : : ] ‾ -1 0 0 6 - 4/2 - 4 = 0 Fc = valence - bonding/2 - unpaired First one is more stable because its greatest electronegativity is on the most electronegative atom

A 3.1971g penny is dissolved in 250 mL of nitric acid. The resulting Cu 2+ solution has an absorbance of 0.432 at 620 nm in a 1.00 cm cell. The calibration curve prepared from Cu 2+ solutions of varying concentrations has a slope of 281.8 L/mol and a y-intercept of 0.0106. (MM Cu = 63.55 g/mol) a. Calculate the concentration of Cu 2+ in moles per liter. b. Calculate the mass of Cu contained in the penny.

a. 0.00144 b.

Match the best answer from the list. Answers are to be used only once. a. Speed of light b. Relationship between the energy of light and its frequency c. Symbol for the wavelength of light d. The measuring device you will use in today's experiment

a. 3.00 x 10^8 m/s b. E = hv c. λ d. spectroscope

Specify the number of valence electrons for each of the following atoms, molecules, or polyatomic ions. a. Si b. O c. Br d. H e. Co3 2- f. H3O +

a. 4 b. 6 c. 7 d. 1 e. 24 f. 8

For each wavelength of the visible hydrogen emission spectrum, assign the corresponding electron transition in the blank beside it. (Rydberg constant = 1.10 x 10^7 m^-1) a. 410 nm = ______ b. 434 nm = ______ c. 486 nm = ______ d. 656 nm = ______ Possible transitions = 3 → 2 4 → 2 5 → 2 6 → 2

a. 410 nm : 6 → 2 b. 434 nm : 5 → 2 c. 486 nm : 4 → 2 d. 656 nm : 3 → 2

How do you calculate the Rf value for a component in a chromatogram?

Rf = (space between the solvent start and the middle of the component) / (space between the solvent start and the solvent front)

An empty styrofoam cup has a mass fo 7.565g. When the cup is completely filled with water (density = 0.9971 g/mL), the mass is 20.381g. When the cup is emptied of water and then filled with an unknown liquid, the new mass is 25.269. What is the density of the unknown liquid to the proper number of significant figures?

1.377g

Indicate whether each of the following is True or False _____ Only colored substances can be separated and identified by paper chromatography. _____ If a component in a mixture interacts more strongly with the liquid phase, it will travel up the paper strip at a. faster rate than a component that interacts more strongly with the stationary (paper) phase.

False True

Draw the cis isomer of C2H2Cl2. Is it nonpolar or polar? (Electronegativity values : c = 2.5 ; H = 2.1 ; Cl = 3.0)

H H > C == C < Cl Cl polar

Indicate whether the following bonds are polar or nonpolar Electronegativity values : Br = 2.8 ; C = 2.5 ; Cl = 3.0 ; H = 2.1 ; N = 3.0 ; O = 3.5 ; S = 2.5 ; Si = 1.8 a. S--O b. C--Br c. C--H d. S--N

a. polar b. nonpolar c. nonpolar d. polar

Match the features in the chromatogram with the description. a. the solvent front b. the component with the smallest Rf value c. the component with the largest Rf value d. the component which interacts the strongest with the paper phase

a. the line 2cm away from the top ; where the liquid is to stop soaking to b. the streak at the shortest point on the paper c. the streak at the highest point on the paper d. longest streak

Match the best answer from the list. a.) "b" in the Beer's Law equation b.) has units of liter x mol^-1 x cm^-1 c.) equal to -log (%T/100) d.) The observed color of the solution whose absorbance spectrum is 580-630 nm LIST OF ANSWERS : 1. concentration 2. light blue 3. the path length of the solution 4. the absorbance of the solution 5. orange 6. ε 7. percent transmittance

a.) ε b.) absorbance of a solution c.) percent transmittance d.) orange