Chem lab part 1 final

You are given samples of two different compounds, one liquid and one solid. Which sample has the greater density?

Density depends on more than physical state, so it is impossible to know without additional information about the compounds.

What is the primary reason that energy is absorbed during the liquid-to-vapor phase transition?

Energy is needed to offset (overcome) the intermolecular forces in a liquid.

Why does it make sense that noble gas elements like xenon only form compounds with highly electronegative elements like fluorine or oxygen?

Only strongly electronegative elements can pull hard enough to cause unreactive noble gases to share their electrons.

In next week's experiment, you will be measuring temperature as it drops during the evaporation of liquids. Why does the temperature decrease?

The temperature being measured is that of a metal probe, not the liquid itself. Energy is transferred from the probe to the liquid as it evaporates.

If the true value for a measurement of mass is 19.705 g, which of the measurements below is the most accurate? 19.699 g 19.650 g 19.715 g All of these measurements show the same degree of accuracy.

19.699

If the best tool you have for measuring length shows millimeters (mm) as the smallest lines (no lines between millimeter markings), which of the following measurements could be correct? 14.mm 7.23mm .25mm 11.2mm

11.2 mm

A student attempts to accurately measure 25.00 mL of water, using a graduated cylinder. Which set of results below shows the best precision? 23.44 mL, 23.37 mL, 23.41 mL 23.41 mL, 26.22 mL, 25.16 mL 25.1 mL, 24.0 mL, 28.2 mL 22.13 mL, 27.98 mL, 33.23 mL 23.44 mL, 23.37 mL, 23.41 mL

23.44 mL, 23.37 mL, 23.41 mL

How many significant figures are there in the measurement 0.02030 kg?

4

It is impossible to perform an "error free" experiment in the laboratory that generates "perfect" data because

All measurements contain error in the last digit or significant figure. No measuring tool (e.g., balance, ruler, graduated cylinder, et al.) is perfectly calibrated. We work at the "macro" level in the lab (using moles of molecules) and therefore we cannot keep track of every last atom or molecule of the compounds we are measuring.

Density values of elements in the Periodic Table tend to increase from top to bottom. Why does this make sense?

Atomic mass and radius (a measure of volume) both increase from top to bottom in the Periodic Table, but mass increases more, so density increases as well.

Which fundamental stoichiometric concept is the basis for your determination of the unknown copper salt?

Conservation of mass. Percent composition by mass. Balanced equations.

Which of the following does not fit into the category of intermolecular forces? Covalent bonding London Dispersion Forces Hydrogen bonding Dipole-dipole interactions

Covalent bonding

What is most likely to be the limiting reactant in the synthesis of soap?

Fatty acids

At one end of the electromagnetic spectrum, gamma waves have the highest energy (high frequency and short wavelength). At the opposite end, radio waves have the lowest energy (low frequency and long wavelength). Which type of radiation travels more quickly to the earth from the sun?

Gamma and radio waves travel to the earth at the same speed.

Why are bubbles created in this experiment?

Hydrogen gas (H2) is being generated.

Why is glycerol an example of a "useful by-product"?

It can be isolated and used for many other applications. It is non-toxic. It is highly water-soluble.

Bill Nye the Science Guy was particularly impressed by the red light given off by strontium. What is one common use for this brilliant red color?

It causes the color red we see in fireworks.

Why is water considered a "green" solvent?

It is not expensive, toxic, or harmful to the environment.

Why is ethanol considered a "Green" solvent?

It is renewable. It is relatively non-toxic. It is relatively inexpensive.

Why is it important to avoid placing the heated ceramic crucible directly on the laboratory bench?

It will burn the bench top, leaving a permanent mark. The temperature difference may shatter the crucible. It will be easier to knock over the crucible (and possibly be burned by touching it) if it's placed on the lab bench.

During lecture today, which of the following people were featured in videos being totally psyched by the AWESOMENESS of chemistry? (Check all that apply.) Cardi B Jimmy Fallon Steven Colbert Lucy Liu

Jimmy Fallon, Lucy Liu

Which of the following is the weakest type of interaction? Hydrogen bonding Ionic attraction Dipole-dipole attraction London dispersion forces

London dispersion forces

Of all the electronic "domains", why do lone pairs take up the most space around a central atom?

Lone pairs are "non-bonding" and therefore their orbital is not being pulled and elongated by the positively charged nucleus of another atom.

Why does mercury (80 electrons) show only three strong lines in the visible spectrum, while neon (10 electrons) shows more than a dozen lines?

Most electronic transitions result from the excitation of valence electrons (electrons in the outermost orbitals). The number of lines in the visible region corresponds with the energy gaps between available orbitals, not the number of electrons. Energy gaps between orbitals vary from one element to another, depending on the electron configuration and overall number of electrons.

While working in the lab, when is it permissible to remove the mask you are wearing that completely covers your mouth and nose?

Never

What is the correct name for the following compound: NiCl2.5H2O ?

Nickel chloride pentahydrate

Which element is unable to expand its octet in a formal Lewis structure? Sulfur (S) Bromine (Br) Xenon (Xe) Nitrogen (N)

Nitrogen (N)

Based on the VSEPR model, molecules have specific three-dimensional geometries. What determines the geometry for a given molecule?

Number of electronic "domains". Shapes of the atomic and molecular orbitals. Repulsion between electrons.

Why is it important that you not look directly at the sun with your spectroscope?

Radiation from the sun will damage your retina and the tissues within your eye.

When you heat an iron rod, it eventually starts to glow - at first red and then eventually "white hot" as the temperature rises. Why is red the first visible color instead of green or violet?

Red light has the lowest energy of all the colors in the visible region.

The third ionization energy for Boron (B) is larger than the second ionization energy. Why is this the case?

Removing an electron from a 2+ cation always requires more energy than removing an electron from a 1+ cation.

The third ionization energy for Beryllium (Be) is larger than the second ionization energy. Why is this the case?

Removing an electron from a 2+ cation always requires more energy than removing an electron from a 1+ cation. The third ionization for Beryllium involves removing an electron from a full shell configuration. Beryllium cations prefer to be isoelectronic with Helium rather than Hydrogen.

You have samples of three different solids as shown below. All three samples occupy the same volume. Which sample has the greatest density? Sample 1 (mass = 10.743 g) Sample 2 (mass = 17.232 g) Sample 3 (mass = 5.977 g)

Sample 2

You have three samples of liquid as shown below. All three samples have the same mass. Which liquid has the lowest density? Sample 1 (volume = 25.64 mL) Sample 2 (volume = 53.27 mL) Sample 3 (volume = 71.22 mL)

Sample 3

Phosphates used to be common additives in detergents. Why is this no longer the case?

Scientists have developed better alternatives. It's important to address the broader impact of the chemicals we release into the environment. Industry, scientists, and politicians worked together to address the environmental impacts of phosphates.

What is the correct spelling of the verb that means "to divide into constituent or distinct molecules"?

Separate

Why is it required that you only make markings on chromatography paper with a dull pencil?

Sharp pencils may tear the paper. Ink may smear and obscure the results from the dye samples. Ink actually contains dye molecules, while graphite does not.

Which electronic "domain" requires the least amount of space around the nucleus of an atom?

Single bond

Which of the following molecular properties could be exploited to distinguish between different types of substances in a chromatography experiment?

Size (molar mass), Polarity, and Charge

Proper set-up of the filtration apparatus requires that the filter paper completely cover all holes in the Buchner funnel. Why is this?

So no copper product is lost through the funnel.

Soap molecules are typically quite large. Why are they able to dissolve in water?

Soap molecules have a highly polar/ionic portion that helps dissolving by interacting with water molecules.

Which of the following metals is most likely to give up its valence electrons to form a cation? Sodium (Na) Silver (Ag) Gold (Au) Copper (Cu)

Sodium (Na)

Which physical phase could not be used as the "mobile phase" in a chromatography experiment?

Solid

As we discussed in lecture today, the melting points of elemental carbon (C) and nitrogen (N) are remarkably different. What is the best explanation for this?

The difference in valence electrons between these two elements: carbon forms extended three-dimensional networks like diamond and nitrogen forms highly stable molecules consisting of only two atoms.

Most of the time, hydrates of salts are a different color than the respective anhydrous salts. What is the explanation for this?

The inclusion of water molecules in the crystal lattice changes the relative energies of metal electron orbitals.

Why is it important to continue cycles of heating the ionic compounds until a constant mass is recorded?

Two consecutive mass measurements means that all the water has been removed through the heating process. Incomplete removal of water from the crystal lattice will lead to erroneous stoichiometric calculations. Different salts contain different amounts of water and some may take more heating than others to be sure all water is removed.

Which of the following is NOT true about the inclusion of water molecules in the crystal lattice of an ionic compound? Water molecules occupy specific, fixed positions in the crystal lattice. Water molecules are positioned randomly throughout the crystal lattice. The partial positive side of water molecules are positioned near the anions of the ionic compound. The partial negative side of water molecules are positioned near the cations of the ionic compound.

Water molecules are positioned randomly throughout the crystal lattice.

Why has the use of synthetic detergents like "sodium laurel sulfate" been strictly curtailed in the U.S. and elsewhere?

When released to the environment, these molecules cause foaming in streams, lakes, and oceans. Scientists have designed better (greener, more effective, less environmentally harmful) molecules for use in detergents. These molecules do not degrade properly in wastewater treatment plants.

As we discussed in lecture, the Noble Gases (Group 18) were among the last elements to be "discovered" and added to the Periodic Table. Why is this?

With full valence shells, these elements are extremely unreactive and (mostly) don't form compounds with other known elements. The elements in this group are all gases at room temperature and pressure. These elements are all odorless and colorless.

Oxidation-reduction reactions are chemical reactions that always include

transfer of electrons from one species to another.