Chem 101L Quizzes

Using the graph shown from an experiment measuring the density of water, what would be the correct value, units, and significance of the slope of the trendline?

. -8.92 x 10-4 g mL-1 oC-1 represents the change in density as temperature increases

In a conductivity titration, 10.15 mL of 4.95 x 10-3 M Ba(OH)2 is titrated by a 4.15 x 10-3 M H2SO4 solution. The end point of the titration would be expected at a volume of:

12.11 mL

When calculating the displacement volume of the thermometer, the volume reading on the buret is 28.47 mL without the thermometer, and 27.82 mL with the thermometer in place. How many significant figures should be recorded for the displacement volume of the thermometer?

2

The following equations represent reactions used in Experiment 5. Of these reactions, choose the correctly balanced propulsion reaction.

2 H2 (g) + O2 (g) → 2 H2O (g)

The volume marking at the sealed bottom of a buret segment is 48.60 mL, and has markings for every 0.1 mL. When water is added, the bottom of the meniscus sits about halfway between the line for 28.3 mL and the next mark up. What volume of water is contained in the buret segment?

20.35 mL

According to the stoichiometry of the exothermic reaction equation 2 HCl (aq) + Mg (s) → H2 (g) +MgCl2 (aq), the maximum energy that can be released by this reaction would occur at a HCl:Mg ratio of

2:1

Given the Rydberg equation: ΔE = RH (1/(nf2)- 1/(ni2)) In the Balmer series for hydrogen, what is the initial energy level (ni) for a photon with a wavelength of 434.1 nm? REMEMBER: h = 6.626 x 10-34 J⋅s; c = 2.998 x 108 m/s; RH = 2.18 x 10-18 J

5

The graph shows the calibration of a spectroscope against a series of emission lines of known wavelength. Based on this calibration, which is the wavelength of a line that appears at 5.34 mm on the spectroscope scale?

535 nm

When viewed through a spectroscope, calcium ions produce three distinct lines in the visible region of the spectrum, at spectroscope positions of 7.30, 7.85, and 8.45. Assuming the linear fit for the calibration of the spectroscope has a positive slope, the line corresponding to the lowest energy would have a spectroscope position of:

8.45

In a calorimetry experiment, 50.0 mL each of two dilute aqueous solutions are combined and produce an extrapolated ΔT = -22.4˚C. If the density of each solution is assumed to be equal to that of water (at 20˚C, d = 0.9982 g/mL), and the specific heat of the solution is also equal to that of water (4.186 J/g˚C), the value of qrxn would be:

9.36 kJ

In the reaction NaOH(s) + HCl (aq) → NaCl(aq) + H2O(l), the spectator ion(s) would be: (select all that apply.)

: Cl-

A conductivity plot for the titration of barium hydroxide with sulfuric acid is shown below. Assuming sulfuric acid is the titrant, which ion species would you expect to be significant in solution when 11.62 mL of titrant had been added?

B and C only ( SO42- and H+)

The molecular equation for the reaction in Experiment 4 is: Ba(OH)2 + H2SO4 →BaSO4 + 2 H2O Based on the conductivity properties of these reactants and products that you observed in the lab, which is the correct net ionic equation?

Ba2+(aq) + 2 OH-(aq) + 2 H+(aq) + SO42-(aq) →BaSO4(s) + 2 H2O(l)

In calorimetry, the enthalpy change of the reaction, qrxn, is defined to be: (Select all that apply.)

Both A and E are true ( -(qsoln + qcal) and the heat gained or lost by the reaction in units of joules.)

During a conductivity titration, 15.0 mL of Ba(OH)2 is placed in a beaker with 35 mL of H2O. At the start of the titration, the initial conductivity reading is nearly double that of a previous trial and does not decrease to zero at the minimum as expected as sulfuric acid is added, even though the minimum occurs at the expected volume. One possible explanation for these observations would be:

Instead of adding distilled water to the barium hydroxide, the experimenter added tap water.

Using the graph provided, for the reaction of 1.25 g of sodium bicarbonate with 150 mL of 0.5 M citric acid, the value of ΔT/mol (°C/mol) would be: (NOTE: molar mass of sodium bicarbonate is 84.007.)

None of these

To carry out Experiment 6 quantitatively, one major adjustment was made to the procedure followed in Experiment 2. That adjustment was:

The calorimeter was calibrated to account for heat loss from the system.

A student creates the following graph after an experiment measuring the density of water. Suppose the thermometer the student used was improperly calibrated and always read a value 3.5 degrees below the true temperature. Which of the following statements would be true?

The slope of the regression line would be correct, but the intercept would read a value that was less than the true value.

Which item used during Experiment 8 required calibration?

The spectroscope.

The molecular equation of a reaction is NaHCO3 (aq) + HCl (aq) →NaCl (aq) + H2O (l) + CO2 (g). Both the initial solutions and the final solution were transparent and colorless, but bubbles were seen during the reaction. Based on this equation and the observations of the reaction, the spectator ions in the ionic equation would be:

Two of the above A. Na+ B. Cl- C. H+ D. CO2 E. H2O

Based on your observations in Experiment 5, an exothermic reaction may be identified via observation in the lab when it:

Two of these answers are correct. (Causes a loud popping noise)

The temperature at the start of a reaction was 22.8°C and the final temperature was 32.9°C. Based on these observations, the reaction of sodium bicarbonate with hydrochloric acid would be:

exothermic, because energy is transferred from the reaction to the surroundings

The following three actions could produce a significant source of error in the results for Experiment 5: Using an excess of yeast in the reaction with H2O2. Using an excess of HCl in the reaction with zinc. Collection both gases in the same pipet bulb.

false

3.5 g of white solid is added to a calorimeter containing 30 mL of 0.5 M HCl at 22 °C. During the reaction, bubbles appear in a steady stream, and the solution remains transparent. Based on these observations the reaction would be classified as:

two of the above (gas-forming and..)