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# Recently Posted Questions in Chemistry

Tracem-p outlines potential hazards and mechanisms of injury at a hazardous materials (hazmat) incident. the letter “t” stands for:

Tracem-p outlines potential hazards and mechanisms of injury at a hazardous materials (hazmat) incident. the letter “t” stands for Thermal.

Monel metal is a corrosion-resistant copper-nickel alloy used in the electronics industry. A particular alloy with a density of 8.80 g/cm3 and containing 0.073% Si by mass is used to make a rectangular plate that is 15.0 cm long, 12.5 cm wide, and 2.50mm thick and has a 2.50-cm-diameter hole drilled through its center such that the height of the hole is 2.50mm . The silicon in the plate is a mixture of naturally occurring isotopes. One of the those isotopes is silicon-30, which has an atomic mass of 29.97376 amu and a percent natural abundance of 3.10% How many silicon-30 atoms are found in this plate? Express your answer numerically using two significant figures.

Answer is: there are 1.82·10²⁰ silicon-30 atoms.

V₁(alloy) = 15 cm · 12.5 cm · 0.25 cm.

V₁(alloy) = 46.875 cm³; volume of the alloy without hole.

V(hole) = 0.25 cm · (1.25 cm)² · 3.14.

V(hole) = 1.23 cm³

V₂(alloy) = 46.875 cm³ - 1.23 cm³.

V₂(alloy) = 45.65 cm³; volume of the alloy with hole.

m(alloy) = V₂(alloy) · d(alloy).

m(alloy) = 45.65 cm³ · 8.80 g/cm³.

m(alloy) = 401.7 g; mass of the alloy.

ω(Si) = 0.073% ÷ 100%.

ω(Si) = 0.00073.

m(Si) = ω(Si) · m(alloy).

m(Si) = 0.00073 · 401.7 g.

m(Si) = 0.293 g; mass of silicon it the alloy.

m(Si-30) = m(Si) · ω(Si-30).

m(Si-30) = 0.293 g · 0.031.

m(Si-30) = 0.0091 g; mass of the silicon-30.

n(Si-30) = m(Si-30) ÷ M(Si-30).

n(Si-30) = 0.0091 g ÷ 29.97376 g/mol.

n(Si-30) = 0.000303 mol; amount of the silicon-30.

N(Si-30) = n(Si-30) · Na (Avogadro constant).

N(Si-30) = 0.000303 mol · 6.022·10²³ 1/mol.

N(Si-30) = 1.824·10²⁰.

A chemist has 2.0 mol of methanol (CH₃OH). The molar mass of methanol is 32.0 g/mol. What is the mass, in grams, of the sample? 16 30 32 64

64

Explanation:

Mole of a compound = mass of a compound / molar mass of a compound

Mass of a compound = mole of a compound x molar mass of a compound

Given,

Mole of methanol = 2 mol

Molar mass of methanol = 32 g/mol

Mass of methanol = Mole of methanol x Molar mass of methanol

= 2 mol x 32 g/mol = 64 g

Therefore, the mass, in grams, of the sample = 64

Draw a complete Lewis structure for the conjugate acid of nitromethane that shows all bonds, unshared electron pairs, and minimized formal charges, where appropriate.

Lewis structures are shown below

Explanation:

• In Lewis structure of nitromethane, a negative charge is present on oxygen atom in nitro group.
• Hence this oxygen atom acts as a basic center preferably.
• Therefore conjugate acid of nitromethane should be drawn by adding a hydrogen atom with this oxygen atom.
• Lewis structure of nitromethane as well as it's conjugate acid has been shown below including all the lone pairs and formal charges

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An unknown compound contains only carbon, hydrogen, and oxygen (CxHyOz). Combustion of 2.50g of this compound produced 3.67g of carbon dioxide and 1.50g of water. How many moles of carbon, C, were in the original sample?

The solution to the problem is as follows:

a)

C + O2 = CO2

Molar mass CO2 = 44 g/mol

3.67 g CO2 * 1 mol / 44 g =

=0.0834 mol CO2 = 0.0834 mol C

I hope my answer has come to your help. God bless and have a nice day ahead!

What kind of bond does these have? 1.tap water 2.distilled water 3.sugar 4.salt 5.salt in distilled water 6.sugar in distilled water

1. Tap water has a small concentration of H+ & OH- ions as well as water molecules, hence there would be permanent dipole-permanent dipole (p.d.-p.d.) forces of attraction between the water molecules (aka H-bonds) as well as ionic bonds between the H+ & OH- ions.

2. Distilled water does not have H+ & OH- ions, hence only H-bonds exist between the water molecules.

3. There are covalent bonds between the individual sugar molecules.

4. There are ionic bonds between the Na+ & Cl- ions in NaCl.

5. There are p.d.-p.d. forces of attraction between the Na+ ions and the O2- partial ions of the water molecules as well as between the Cl- ions and the H+ partial ions of the water molecules. There are also H-bonds between the individual water molecules and ionic bonds between the Na+ & Cl- ions (although these are in much lower abundance than in unsolvated solid NaCl).

6. There are i.d.-i.d. as well as p.d.-p.d. forces of attraction between the sugar molecules and the water molecules. There are also H-bonds between the individual water molecules and covalent bonds within the sugar molecules.

A teacher makes the following statement. “Gasoline boils at a relatively low temperature (about 150°C). The kerosene is removed at around 200°C, followed by diesel oil at 300°C and fuel oil at around 370°C.” What topic is the teacher most likely talking about? a. distillation of a mixture b. filtration of a pure substance c.evaporation of a mixture d. sorting of a pure substance

The correct answer is option a.

Explanation:

According the question, boiling points of different liquids are discussed which means that if we take all these liquids in single mixture we can separate them from each other on the basis of their difference in boiling point. And the technique which employs this principle is distillation process.

Hence, we can say teacher is most likely talking about distillation of a mixture of oils.

Distillation is a process which is used to separate mixture of different liquids from each other. In this process, during the course of boiling of mixture liquid compound with lower boiling points vaporizes first leaving behind the liquid with higher boiling point behind.

And vapors of boiled liquid are condensed down in a separate container for the collection.

Which of the following ions would represent the ion of an element from Group 2A? A. X2- B. Y3+ C. Z+ D. A2+

An element belongs to particular group is related to the number of electrons present in the outer shell of the atoms. In given case, group is 2, therefore, number of valence electrons is 2 implies it has ability to lose two electrons to get +2 charge.

Therefore, ion formed after removal of two electrons is .

Hence, option (D) is the correct answer.

Choose one property of water that makes it unique describe the property and explain the chemical or physical reasons that causes water to have to property.

Water has high heat specific capacity. Heat specific capacity is the amount of heat that is needed to raise the temperature of one gram of particular substance by one degree Celsius. The high specific heat capacity of water is due to the hydrogen bond that exist among the molecules of water. The hydrogen bond is quite strong and it will take a lot of heat to break the bonds. Thus, it takes a lot of heating to increased the temperature of water by one degree Celsius. This is also the reason why water has high boiling point.

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Which contributes to the dissolution of sugar in water? a. the dissociation of an ionic compound in water b. a strong pull of water molecules on an ionic compound c. the dissociation of a polar covalent compound in water d. a strong pull of water molecules on a polar covalent compound

Option C: The dissociation of a polar covalent compound in water.

Sugar is made up of sucrose molecules containing polar covalent bonds. They have same type of oxygen-hydrogen covalent bonds that are present in water.

Since, sugar is not an ionic compound, option a and option b are incorrect. Also, due to same type of bonding in water and sugar molecules there will be no such force of attraction between them, this will opt out the option d.

Thus, dissolution of sugar in water is the dissociation of a polar covalent compound in water and option c is correct.

What is the mass of 5.05×1021 platinum atoms?

Explanation:

According to avogadro's law, 1 mole of every substance occupies 22.4 L at STP and contains avogadro's number of particles.

To calculate the moles, we use the equation:

1 mole of Platinum weighs 195 g

of Platinum weigh =

Thus mass of platinum atoms is 1.6 gram.

Which statement best characterizes chemical reactions? They always occur very quickly. Their rates vary significantly. Their rates are always slow. They rarely occur in the natural environment.

I think the correct answer from the choices listed above is the second option. The statement that best characterizes chemical reactions would be that their rates vary significantly. Each reaction has its own rate and it depends on the conditions the reactants are subjected to. Hope this answers the question.

Which of the following is not an example of a polymer? Plastic Nylon Amino acid Polystyrene

I believe the correct answer from the choices listed above is the third option. It is amino acid that is not an example of a polymer. It  is a large molecule, or macromolecule, composed of many repeated subunits. Hope this answers the question.

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Which statement about van der Waals forces is true?

Van der Waals forces' is a general term used to define the attraction of intermolecular forces between molecules. They  are the residual attractive or repulsive forces between molecules or atomic groups that do not arise from a covalent bond, or ionic bonds. Hope this answers the question.

Identify the group of elements that corresponds to the following generalized electron configuration: [noble gas]ns 2 (n−1)d 2

For the answer to the question above, I think you are referring to the group of four elements. The Titanium, Zirconium, Hafnium and lastly the Rutherfordium are the group of elements that corresponds to the configuration you are asking.
I hope my answer helped you

An unknown or changeable quantity is called a(n)...

I think the answer would be dependent variable. An unknown or changeable quantity is called a dependent variable. It is what you measure in the experiment and what is affected during the experiment. Hope this answers the question. Have a nice day.

How many grams does 23 moles of tantalum contain ?

mTa= MTa x nTa

nTa = 23moles

MTa = 180.95 g/mol

so the mTa= MTa x nTa= 4161,85g

Which of these is a property of a substance that is composed of atoms that are held together by ionic bonds? It can be shaped into wires. It has a low melting point. It conducts electricity when in solid form. It conducts electricity when it is dissolved in water.

Explanation:

A ionic compound will have opposite charges on the 2 atoms attached to each other.

When ionic compound is in solid state then atoms will be more closer to each other and also due to the opposite charges the molecules will have strong force of attraction between them.

In order to conduct electricity, free movement of ions is required. So, a solid with ionic bonds is not able to conduct electricity as molecules or ions are closely held together.

Whereas when a substance that is composed of atoms that are held together by ionic bonds is dissolved in water then its ions will start to move freely from one point to another. Thus, this solution will be able to conduct electricity.

Thus, we can conclude that out of the given options, conducts electricity when it is dissolved in water displays a property of a substance that is composed of atoms that are held together by ionic bonds.

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Which fat is most likely a solid at room temperature? one that is saturated one that is unsaturated one with double bonds one that contains no hydrogen

Explanation:

When a fat contains high proportion of fatty acid molecules which have no double bonds then it is known as a saturated fat.

For example, animal fats are mostly saturated.

Fats which are solid at room temperature are known as solid fats. Butter, beef fat etc are all solid at room temperature. Most of the animal food gives solid fats.

Thus, we can conclude that saturated fat is most likely a solid at room temperature.

A machine is a device that creates energy

FALSE!
We can't create or destroy energy. Machine is a device that converts one form of energy into another.

Hope this helps!

What is gas in matter

Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or compound molecules made from a variety of atoms (e.g. carbon dioxide).

Which grouping has the least complex body plan? If you were on a research expedition in the kingdom of Tonga, a coral atoll in the South Paciﬁc, would you ﬁnd these organisms?

YES, I WOULD FIND THOSE ORGANISMS.

The Kingdom of Tonga is a Polynesian Archipelago in Oceania consisting of 176 islands. During a month long coral reef research mission in Tonga, the Foundation focused on islands in the Ha’aipi group, Vava’u and Niuatoputapu. Haʻapai, directly west of the Tonga trench in the central part of Tonga, is made up of 51 volcanic islands and includes Kao, the highest point in the kingdom (1,046 m). Vavaʻu has one large island and 40 smaller ones, and includes the second largest city, a large harbor.  The north side of the main island is lined by 200 m high cliffs and extensive open network of fjord-like channels that stretch inland on the north side. Nearly 300 km north of Vavaʻu, close to the border of Samoa is Niuatoputapu, a sparsely inhabited (population 150)  eroded remnant of a volcano surrounded by a large uplifted reef. This island was badly damaged by a tsunami following a submarine earthquake off Samoa in 2009.

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