Question

Which substance is this?

Answer 1

The substance in question is likely heptane with a molecular formula of C7H16. By calculating its specific heat and comparing it to known values in Table 5.1, its identity can be determined. Additionally, deciding whether a substance is pure or a mixture, and identifying molecular types, requires understanding chemical composition and bonding modes.

Step-by-step explanation:

The substance in question appears to be heptane, which is a hydrocarbon with the molecular formula C7H16. To identify a substance through its specific heat, you would consult a table (such as Table 5.1 referenced in the question), which lists specific heats of various substances. By using the specific heat value of the unknown substance and comparing it to the table, you can often determine its likely identity. The process involves calculating the specific heat using the formula specific heat = amount of heat energy (J) / (mass of the substance (g) * change in temperature (°C)), then matching this calculated value to known substances.

To determine if a substance is pure or a mixture, and if it's homogeneous or heterogeneous, you examine its composition. Pure substances include elements and compounds with uniform composition, while mixtures can be separated into their individual substances and include homogeneous mixtures (solutions) and heterogeneous mixtures with visibly different phases or parts.

The questions regarding identifying molecules and writing molecular formulas involve understanding the types of chemical bonds and molecules. A covalent substance is made up of molecules held together by covalent bonds (sharing of electron pairs), an ionic substance is composed of charged ions held together by ionic bonds (electrostatic attraction), and a metallic substance consists of a lattice of metal cations surrounded by a sea of delocalized electrons.

Answer 2

the substance is most likely a metal.

Step-by-step explanation:

The key pieces of information are:

• 18.58 grams of mass
• 5.7 mL of volume
• Density of 3/25 g/mL
• Sinks in water

Taken together, these properties point to the substance being a metal:

• The relatively high density of 3/25 g/mL is typical for metals. Most non-metals have lower densities.
• Metals typically have much higher mass to volume ratios compared to non-metals, due to their dense crystalline atomic structure. This is consistent with the provided mass and volume.
• The fact that the substance sinks in water suggests it has a high density, again pointing to it likely being a metal. Most non-metals float in water due to their lower density.
• The measurement of mass in grams and volume in mL suggests a real-world substance as opposed to an idealized one, further implying it's a metal.

So in summary, given the provided properties of relatively high mass and low volume but high density, along with sinking in water, the substance is most consistent with being a metal, likely a metal piece or sample of that mass and volume. While other possibilities cannot be ruled out definitively, the available information points most strongly toward the substance being a metal, likely one with a density around 3 grams per cubic centimeter.

#2nd edit:

Based on the limited information, here are my best estimates of what metal it could potentially be:

Best Guess #1: Lead

Lead has a relatively high density of 11.34 g/cm3, which is in the ballpark of the given density of 3/25 g/mL or 12 g/cm3.

Lead has a low melting point of 327 degrees Celsius, which is typical for dense metals.

Lead is a soft, malleable metal that can form into samples of various sizes and masses.

Lead is inexpensive and commonly found in the forms of sheets, rods, pipes, plates, etc. making a sample of around 18 grams plausible.

Best Guess #2: Tin

Tin has a density of 7.3 g/cm3, which is slightly lower but reasonably close to the given density.

Tin is a soft metal that can be molded or cut into small samples weighing around 18 grams.

Tin has a low melting point of around 230 degrees Celsius, consistent with dense metals.

Tin corrodes to a silvery-white color when exposed to air, which could produce the given density if the sample includes some corrosion.

Tin is also commonly available and used in various forms.

Those would be my best guesses for possible metals based on the limited information provided. Lead seems most plausible given its higher density and softer nature, though tin is also a reasonable possibility. Of course, there are many other metals that could match as well, but lead and tin are two of the most common options based on their properties aligning with what little we know about the sample.