Questions posted in Chemistry

How many formula units make up 11.4 g of magnesium chloride (MgCl2)?

A mol has several meanings: 1 mol of an atom, molecule or formula unit contains 6.022 x 10^23 atoms or the Avogadro's Number. Therefore, a formula unit is equal to a mole. Calculation of the formula units of magnesium chloride as follows;

11.4 g (1 mol/ 95.21 g) = 0.12 mol or formula unit

ANSWERED AT 28/01/2020 - 01:16 AM


QUESTION POSTED AT 28/01/2020 - 01:16 AM

Which criterion is used to arrange the elements in columns on the periodic table?

Answer:

The elements that have the same outer electronic configuration belong to the same group (column).

Explanation:

Periodic table is a form of classification of chemical elements. In this table, the elements are classified into seven rows and eighteen columns. The horizontal rows are called periods and the vertical columns are known as groups.

The chemical elements are arranged in the order of increasing atomic number. The elements that have the same outer electronic configuration belong to the same group. Whereas, the elements having the same number of shells belong to the same period.

ANSWERED AT 28/01/2020 - 01:12 AM


QUESTION POSTED AT 28/01/2020 - 01:12 AM

As a purchasing agent for a pharmaceutical company, how much chlorine, Cl2, do you need to order to react completely with 500 kg of platinum, Pt, to make cisplatin, PtCl2(NH3)2?

The formula tells you the proportion in mols

2 mols of Cl: 1 mol of Pt

Now use the atomic masses:

Cl: 35.5 g/mol
Pt: 195 g/mol

Then you have these equation:

[2*35.5 g Cl] / 195 g Pt = x / 500 kg Pt

Solve for x.

x = (71 g Cl / 195 g Pt) * 500 kg Pt

x = 182 Kg Cl = 182 kg Cl2.

ANSWERED AT 28/01/2020 - 01:05 AM


QUESTION POSTED AT 28/01/2020 - 01:05 AM

Structurally, what is the difference between the dermis and the epidermis? A. the dermis contains more types of tissue. B. the epidermis consists of mostly adipose cells. C. the epidermis is thicker. D. the dermis is made of mostly dead cells

A is the right answer

there are 2parts of epidermis in a leaf upper epidermis and epidermis is the lower

ANSWERED AT 28/01/2020 - 12:56 AM


QUESTION POSTED AT 28/01/2020 - 12:56 AM

Under which conditions would the solubility of a gas be greatest?

Answer:High Pressure Low Temp would be the most efficient choice

Explanation:

ANSWERED AT 28/01/2020 - 12:55 AM


QUESTION POSTED AT 28/01/2020 - 12:55 AM

Which is true about the dissolving process in water?

In a dissolving process, energy is required to overcome the forces of attraction between the solvent particles. The first step is for the solvent particles to move in order for solute particles to enter the system. This process is endothermic where energy flows into the system. The second step is when solute particles must separate from other solute particles. Lastly, the solute should move between solvent particles.

ANSWERED AT 28/01/2020 - 12:54 AM


QUESTION POSTED AT 28/01/2020 - 12:54 AM

Which of the following structures are tubes? A. Eustachian, Pharynx, Bronchi. B. Cilia, Adenoids, mucous, epiglottis. C. Apex, MAxillary, sphenoidal, ethmoidal?

The correct answer among the choices given is option A. Eustachian, Pharynx, Bronchi are structures that ensembles a tube. The Eustachian tube is a narrow passage from the pharynx to the middle ear. Pharynx is a passageway leading from the oral and nasal cavities to the larynx and the esophagus. Lastly, bronchi is an airway in the respiratory tract.

ANSWERED AT 28/01/2020 - 12:53 AM


QUESTION POSTED AT 28/01/2020 - 12:53 AM

1 How many grams are there in 7.4 x 1023 molecules of AgNO3? 2 How many grams are there in 7.5 x 1023 molecules of H2SO4? 3 How many grams are there in 9.4 x 1025 molecules of H2? PLZ HELP

Answer:

In 7,4.10^{23} molecules of AgNO_3 are 209 g

In 7,5.10^{23} molecules of H_2SO_4 are 123 g

In 9,4.10^{25} molecules of H_2 are 312 g

Explanation:

First remember that 1 mole of any element has 6.02 10^{23} molecules (this number is a constant).

we know that the molecular mass of an element relates the grams of that substance in 1 mol

To calculate how many grams of AgNO_3 are in 7,4.10^{23} molecules we use a rule of three

6,02.10^{23} molecules \longrightarrow 1mol AgNO_3\\7,4.10^{23} molecules\longrightarrow x\\x=\frac{7.,4.10^{23}molecules.1mol AgNO_3 }{6,02.10^{23}molecules}\\x=1.23 mol AgNO_3

The molecular mass of AgNO_3 is 169.87 g/mol

1 mol \longrightarrow 169.87 g\\1.23 mol\longrightarrow x\\x=\frac{1.23 mol. 169.87g}{1 mol} \\x= 209 g AgNO_3

In 7,4.10^{23} molecules of AgNO_3 are 209 g

To calculate how many grams of H_2SO_4 are in 7,5.10^{23} molecules we repeat the previous procedure

6,02.10^{23} molecules \longrightarrow 1mol H_2SO_4\\7,5.10^{23} molecules\longrightarrow x\\x=\frac{7.,5.10^{23}molecules.1mol AgNO_3 }{6,02.10^{23} molecules}\\x=1.25 mol H_2SO_4

The molecular mass of H_2SO_4 is 98.079 g/mol

1 mol \longrightarrow 98.079g\\1.25 mol\longrightarrow x\\x=\frac{1.25mol. 98.079g}{1 mol}\\x= 123 g AgNO_3

In 7,5.10^{23} molecules of H_2SO_4 are 123 g

To calculate how many grams of H_2 are in 9,4.10^{25} molecules we repeat the previous procedure

6,02.10^{23} molecules \longrightarrow 1mol H_2\\9,4.10^{25} molecules\longrightarrow x\\x=\frac{9,4.10^{25}molecules.1mol H_2}{6,02.10^{23} molecules}\\x=156 mol H_2

The molecular mass of H_2 is 2 g/mol

1 mol \longrightarrow 2g\\156 mol\longrightarrow x \\x=\frac{1.25mol. 98.079g}{1 mol} \\x= 312g

In 9,4.10^{25} molecules of H_2 are 312 g

ANSWERED AT 28/01/2020 - 12:51 AM


QUESTION POSTED AT 28/01/2020 - 12:51 AM

How many moles are present in 10.5 grams of NaCl?

Answer : The number of moles present in 10.5 grams of NaCl are, 0.179 moles.

Solution : Given,

Mass of NaCl = 10.5 g

Molar mass NaCl = 58.5 g/mole

Formula used :

\text{Moles of NaCl}=\frac{\text{Mass of NaCl}}{\text{Molar mass of NaCl}}

Now put all the given values in this formula, we get the moles of NaCl

\text{Moles of NaCl}=\frac{10.5g}{58.5g/mole}=0.179moles

Therefore, the number of moles present in 10.5 grams of NaCl are, 0.179 moles.

ANSWERED AT 28/01/2020 - 12:51 AM


QUESTION POSTED AT 28/01/2020 - 12:51 AM

If there is a loss of 5.63 x 10 -7 kg of mass in a nuclear reaction, how many joules of energy would be released? Recall that C equals 3 times 108 m / s.

5.07x10^10 may be right but i dunoo know bro 

ANSWERED AT 28/01/2020 - 12:51 AM


QUESTION POSTED AT 28/01/2020 - 12:51 AM

Which of the following equations can be used to determine the change in enthalpy of a system?

When ever I had to calculate changes in enthalpy I always used the equation q=mcΔT.

I hope this helps.  Let me know if anything is unclear.

ANSWERED AT 28/01/2020 - 12:50 AM


QUESTION POSTED AT 28/01/2020 - 12:50 AM

A. Which statement accurately describes part of the dissolving process of a polar solute in water? B. Solute molecules repel water molecules. C. Water molecules surround solute molecules. D. Water molecules are strongly attracted to nonpolar substances. Solute molecules remain concentrated in one part of the solvent.

A statement that accurately describes the dissolving process of a polar solute in water

C. Water molecules surround solute molecules.

Explanation:

By description, the "solvent" is the major composite and the "solute" is the lesser compound in solution. The roles/names may be modified if the compounds are commonly miscible. Water is an outstanding solvent because its polar water molecules makehydrogen bonds with ions and polar molecules, releasing ionic and polar covalent compounds to scatter easily in water.

ANSWERED AT 28/01/2020 - 12:49 AM


QUESTION POSTED AT 28/01/2020 - 12:49 AM

What is the molarity of a .25 liter solution containing 52 grams of HBr?

Molar mass HBr = 80.91 g/mol

number of moles:

mass of solute / molar mass

52  / 80.91 => 0.642 mols

Volume = 0.25 L

M = n / V

M = 0.642 / 0.25

M = 2.568 mol/L

hope this helps!

ANSWERED AT 28/01/2020 - 12:48 AM


QUESTION POSTED AT 28/01/2020 - 12:48 AM

A mover packs books, CDs, and DVDs into a moving box. If the box contains 6.5 kg of books, 1.5 kg of CDs, and 2.0 kg of DVDs, what is the percent by mass of each object in the box?

Answer:

\text{Mass percentage}=\frac{\text{Mass of the substance}}{\text{Total mass}}\times 100

Given: Mass of books = 6.5 kg

Mass of CD's = 1.5 kg

Mass of DVD's = 2.0 kg

Total mass = 6.5 kg + 1.5 kg + 2.0 kg = 10 kg

\text {Mass percentage of books}=\frac{6.5kg}{10kg}\times {100}=65\%

\text {Mass percentage of CD's}=\frac{1.5kg}{10kg}\times {100}=15\%

\text {Mass percentage of DVD's}=\frac{2.0kg}{10}\times {100}=20\%

ANSWERED AT 28/01/2020 - 12:47 AM


QUESTION POSTED AT 28/01/2020 - 12:47 AM

Which of these factors will cause a solid solute to dissolve faster? increasing the air temperature increasing the amount of solute increasing the amount of solvent increasing the surface area of solute

The correct answer among the choices given is the last option. Increasing the surface area of the solute will increase the dissolution of a solute in the solvent. The dissolution rate is affected by a number of factors like temperature, pressure, particle size and the polarity.

ANSWERED AT 28/01/2020 - 12:46 AM


QUESTION POSTED AT 28/01/2020 - 12:46 AM

Deforestation typically

Deforestation typically leads to soil erosion and the ruin of the ecosystem where deforestation occurred. The land gets destroyed and with it the natural habitat of the animals and plants who live there. In addition, we, the humans, lose oxygen because of lack of trees.

ANSWERED AT 28/01/2020 - 12:46 AM


QUESTION POSTED AT 28/01/2020 - 12:46 AM

When a strip of magnesium metal is touched to a flame, a bright light and a whitish substance are produced. Why is the burning of magnesium considered a chemical change? A. because the metal reaches a high temperature B. because the metal begins to melt C. because a new substance is formed D. because the metal is malleable

C. Chemical changes take place when a new substance is formed from an older substance. In this case, a new substance is formed when the magnesium metal is touched to a flame and the heat transforms it into the whitish, powdery substance.

ANSWERED AT 28/01/2020 - 12:44 AM


QUESTION POSTED AT 28/01/2020 - 12:44 AM

A precipitate is the name for the _____ that forms when liquids are mixed? metal, element, solid, gas

It is named a solid,but i thin,k its metal but no its solid
...

ANSWERED AT 28/01/2020 - 12:41 AM


QUESTION POSTED AT 28/01/2020 - 12:41 AM

A fusion reaction takes place between carbon and another element. Neutrons are released, and a different element is formed. The different element is A) lighter than helium.B)heavier than helium.C)the same weight as helium.D)dependent on the element that reacted with carbon.

Answer is: B) heavier than helium.

Helium (He) is an element with mass number 4 and carbon (C) is an element with mass number 12. Carbon has three time bigger mass numer, so new element is heavier thah helium.

For example, nuclear reaction: ²⁴⁹Cf + ¹²C → ²⁵⁷Rf + 4n°.

Californium-249 has mass number 259, carbon-12 has mass number 12 and rutherfordium-257 has mass number 257.

Mass number (A) is the total number of protons and neutrons in a nucleus.  

Sum of mass numbers of californium-249 and carbon-12 is 261 (249 + 12), but four neutrons are produced, so new element has mass number 257 (261 - 4).


ANSWERED AT 28/01/2020 - 12:39 AM


QUESTION POSTED AT 28/01/2020 - 12:39 AM

Which of the following observations would indicate that a material is a pure substance? A. It does not dissolve in water. B. It changes color after heating. C. It cannot be physically broken down into different types of atoms. D. It can be physically broken down into different types of molecules.

The answer to the question is the option C. it cannot be physically broken down into different types of atoms. This means that the material is an element, which is a pure substance. Because an element is a pure substance that is formed by one only type of atoms. For example, gold is an element and all its atoms are of the same type. That is also true for any of the 118 elements of the periodic table. Compounds (other kind of pure substances) can be broken down into molecules (which contain different kind of atoms, but always in the same proportion) and mixtures (non pure substances) have different kind of substances.

ANSWERED AT 28/01/2020 - 12:37 AM


QUESTION POSTED AT 28/01/2020 - 12:37 AM

One quarter of a 1-mole piece of iron turns to rust in six months. Which rate describes the speed at which the iron rusts?

Answer:

0.5 mol/yrs

hope this helps!

ANSWERED AT 28/01/2020 - 12:36 AM


QUESTION POSTED AT 28/01/2020 - 12:36 AM

Which best describes what happens when 50 mL of 0.0010M CaCl2 is added to 50 mL of 0.010M Na2SO4? (The Ksp of CaSO4 = 2.4 × 10–5.)

For [Ca +2 ]:
0.0010 mol/l · 0.05 l = 5 * 10^{-5} mol
For [ SO4 -2 ] :
0.01 mol/l · 0.05 l = 5 * 10^{-4}
Cumulative volume:
 50 ml + 50 ml = 10 ml = 0.1 l
[Ca +2 ] = \frac{5 * 10^{-5} }{0.1} = 5 * 10^{-4}
[SO4 - 2] =  \frac{5*10^{-4} }{0.1}= 5* 10 ^{-3}
Qc for CaSO4:
Qc =  5 * 10 ^{-4} * 5 * 10^{-3} = 25 * 10 ^{-7}= 2.5 * 10 ^{-6}
This is less than Ksp of CaSO4. 
 Answer: C ) No precipitation will occur.

ANSWERED AT 28/01/2020 - 12:36 AM


QUESTION POSTED AT 28/01/2020 - 12:36 AM

If sulfur dioxide and oxygen can be made into sulfur trioxide, what is the reverse reaction?

Sulfur monoxide, I believe.

ANSWERED AT 28/01/2020 - 12:34 AM


QUESTION POSTED AT 28/01/2020 - 12:34 AM

In a first-order reaction, how does the rate change if the concentration of the reactant decreases to one-third its original value?

Changes at the rate of 3 or the third rate

ANSWERED AT 28/01/2020 - 12:34 AM


QUESTION POSTED AT 28/01/2020 - 12:34 AM

How many kilojoules of heat energy are required to raise the temperature of 400.0g of water from 18.0ºC to 25.0 ºC?

Q=mcdeltaT
Q=400*4.18J/g*7
Q=11704J

ANSWERED AT 28/01/2020 - 12:33 AM


QUESTION POSTED AT 28/01/2020 - 12:33 AM

Which description best characterizes the motion of particles in a solid

The movement of particles within a solid is extremely slow when compared to that of a gas. It is also significantly slower in movement than that of the movement found within the particles of liquid. The more movement present and the faster the movement of the particles the more space will be present between each particle. This causes the material to spread out as they become less densely packed within a solid material.

ANSWERED AT 28/01/2020 - 12:32 AM


QUESTION POSTED AT 28/01/2020 - 12:32 AM

What are thermal plasmas

Have electrons and the heavy particles at the same temperature, i.e. they are in thermal equilibrium with each other.

ANSWERED AT 28/01/2020 - 12:31 AM


QUESTION POSTED AT 28/01/2020 - 12:31 AM

Which statement describes a chemical property of water? It reacts with sodium metal. It has a melting point of 0°C. It has a density of about 1 g/mL. It is clear and colorless.

The chemical description of water is H2O, which means, it is composed of 2 hydrogen atoms and 1 oxygen atom. The answer to this item is the fourth option, " It is clear and colorless." When water is added with calcium, clear, colorless bubbles are formed. This explains a reaction of water with acid. The following are additional facts about water properties: Density: 1 g/cm³ Boiling point: 100 °C Molar mass: 18.01528 g/mol Melting point: 0 °C Formula: H2O

ANSWERED AT 28/01/2020 - 12:14 AM


QUESTION POSTED AT 28/01/2020 - 12:14 AM

Simiralities of bohr's atomic model and Rutherford's atomic model?

There are a lot of similarities between the two models.
Rutherford said that electrons revolve around the nucleus in rings.

Bohr also said it but in a slightly modified way.

He said that the orbits could have only certain fixed sizes depending on their allowed energies.

In an address to the Physical Society of Copenhagen, Bohr stated,

"It can be seen that it is impossible to employ Rutherford's atomic model so longas we confine ourselves exclusively to ordinary electrodynamics".

Bohr introduced the concept of electron shells.

Bohr did not prove that Rutherford was wrong. Rather, he improved and extended the Rutherford model.

There were two drawbacks to the Rutherford model.

It does not explain the hydrogen spectrum.It does not obey Maxwell's equations, which predict that an orbiting electron should fall into the nucleus.

Bohr's model is a defined, expanded model of Rutherford's atom that overcomes these two drawbacks.

The basics are the same, i.e., electrons revolve around the nucleus in paths called orbits with the nucleus at the centre.

Bohr expanded on Rutherford's model in detail.





ANSWERED AT 28/01/2020 - 12:12 AM


QUESTION POSTED AT 28/01/2020 - 12:12 AM

Which statement describes a chemical property of water? It reacts with sodium metal. It has a melting point of 0°C. It has a density of about 1 g/mL. It is clear and colorless.

The statement that describes a chemical property of water is this: IT REACT WITH SODIUM METAL.

Substances generally have two types of properties, these are chemical and physical properties. Physical properties of matters refer to those characteristics of matter which can be observed without changing the composition or nature of the matter. Examples of physical properties are color, boiling point, melting point, etc. Chemical properties on the other hand are those properties that can only be observed by changing the chemical nature of the substance. For instance, the chemical reaction of a substance with another substance will showcase the chemical properties of those substances.

ANSWERED AT 28/01/2020 - 12:11 AM


QUESTION POSTED AT 28/01/2020 - 12:11 AM