How would you prepare 250 mL of 0.125 M HCl from concentrated HCl (aq) that is 38.0% by mass with a density of 1.19 g/mLnote: find moles in 250 mL of 0.125 HCl

Half life is the time period in which half of the initial amount of an element will decay into a new element due to instability. For I-131, the half life is 8 days.

From 200 to 25 grams, let's see how many half lives are there:

200g -> 100g

100g -> 50g

50g -> 25g

Therefore for 200g of I-131 reach 25 grams, 3 half lives are necesseray, 3 half lives or 24 days

2. (a) We are told that it is a double displacement reaction, so there will be two substitutions and Cl will exchange places with NO3.

Now, that will be the full reaction but we need to balance it. Count the atoms of each element on each side of the reaction. In the figure we can see that Chlorine, Nitrogen and Oxygen are not balanced.

We place the coefficient 2 in front of the AgCl molecule to balance the chlorides. You can see the picture.

Now we will balance the nitrogens. There are two nitrogens in the products. We place the coefficient two in the AgNO3 molecule. In the figure I will make the update.

Now the equation is balanced, so the balanced reaction will be:

The question requires us to calculate the pOH value for a solution containing 0.01 moles of HCl in 2.5 L of solution.

To solve this problem, we'll need to go through the following steps:

I) calculate the molar concentration of the HCl solution to obtaine the concentration of H+ ions;

II) using the concentration of H+ ions, calculate the pH of the solution;

III) with the value obtained for pH, calculate the value of pOH for this solution.

Next, we'll go through the steps to solve the question:

I) Since the question provided the number of moles of HCl and the volume of the solution, we can calculate the molar concentration using the following equation:

Thus, applying the values provided:

Therefore, the concentration of the HCl solution is 0.004 mol/L.

Since HCl is a strong acid, we can expect it to completely dissociate in H+ and Cl-: the concentration of H+ ions for this solution would also be 0.004 mol/L ( [H+] = 0.004 mol/L).

III) The next step is calculate the pH of this solution. We'll use the following equation and apply the concentration of H+ ions obtained in the previous step ( [) using H+] = 0.004 mol/L):

Now, we know that the pH of the solution is 2.39.

III) The last step is use the pH value calculated (pH = 2.39) to calculate the pOH of the solution, using the following equation:

Therefore, the pOH of the HCl solution given is 11.6.

pH = 7

pOH = 7

The formula for calculating the pOH of a solution is given as:

Given the following parameter

Substitute

Determine the pH of the solution

Recall that pH + pOH = 14, hence;

Hence the required pH and pOH of aqueous solution are 7 and 7 respectively

Explanation:

One atm of pressure is equal to 760 torr. We can use this relationship to find the answer to our problem.

1 atm = 760 torr

P = 2.29 atm = 2.29 atm * 760 torr/(1 atm)

P = 1740 torr

Answer: The pressure of the tank in torr is 1740 torr.

The groups of the periodic table from left to right are alkali metals, alkaline earth metals,transition metals,halogens and noble gases.

Periodic table is a tabular arrangement of elements in the form of a table. In the periodic table, elements are arranged according to the modern periodic law which states that the properties of elements are a periodic function of their atomic numbers.

It is called as periodic because properties repeat after regular intervals of atomic numbers . It is a tabular arrangement consisting of seven horizontal rows called periods and eighteen vertical columns called groups.

Elements present in the same group have same number of valence electrons and hence have similar properties while elements present in the same period show gradual variation in properties due to addition of one electron for each successive element in a period.

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0.268grams

According to the Avogadro's constant

1 mole of an atom = 6.02 * 10^23 molecules

Given the following

atoms of calcium = 4.02 x 10^21 atoms

Determine the moles of calcium

Determine the mass of Calcium

Hence the required grams in 4.02 x 10^21 atoms of calcium is 0.268grams

DNA describes as a blueprint for a cell because it contain the instruction needed for an organism to grow develop and survive

DNA is called a blueprint of life because it contain the instruction needed for an organism to grow develop and survive and reproduce and DNA does this by controlling protein synthesis and protein do must of the work cell and are basic unit of structure and function in the cell of organism

DNA is read by the enzyme RNA polymerase and this enzyme attaches itself to the DNA strand slightly in front of a gene and it then slides along the DNA strand making a copy of the gene only using RNA building blocks instead of DNA building block

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In order to solve the question b):

We have the following reaction occuring:

We need to calculate the number of moles of aluminum needed to produce 30ml of H2 (hydrogen gas) at a temperature of 22°C and a pressure of 763mmHg.

To calculate the number of moles of hydrogen produced we use the ideal gas equation:

Where:

P is the pressure

V is the volume

n is the number of moles

R is the gas constant

T is the temperature

R is a constant and it's value is:

So we need to convert each variable to the units of this constant.

So now we calculate:

So we know that 0.00124 moles of H2 are formed.

Now we know that for every 2 moles of aluminum 3 moles of H2 are formed.

So we calculate the moles of Al needed:

So the answer is 0.000826 moles of Al°

option A is  is a true molecular equation depicted.

Na2S+2HCl→2NaCl+H2S↑

A molecular equation is a balanced chemical equation in which the constituent ions of the ionic compounds are represented as molecules. Each of a compound's constituent components and the amount of atoms they each possess are listed in the molecular formula. Similar rules apply to the most basic formula: all the constituents are mentioned, but the numbers represent their relative proportions.

There are three different types of equations that may be developed for a reaction involving ionic compounds: molecular equations, full ionic equations, and net ionic equations. In chemistry, each of these equations has a specific function. Because it details exactly which compounds were employed in a process, a molecular equation is useful.

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Given the equation:

• Sn (NO2)4 + Pt3N4 → Sn3N4 + Pt(NO2)4

(1) The first thing we noticed is that this is a double replacement equation

• ,Sn combines with N4 to form Sn3N4, (,take note that Sn→ Sn3,)

• Pt3 combines with (NO2) to form Pt(NO2)4 ( ,take note that Pt3 → Pt)

(2) Balancing the equation

• Sn (NO2)4 + Pt3N4 → Sn3N4 + Pt(NO2)4 ....(,place 3 infront of Sn in the reactant side .)

• 3,Sn (NO2)4 + Pt3N4 → Sn3N4 + Pt(NO2)4...( ,then place 3 infront of Pt in the product side,)

• 3,Sn (NO2)4 + Pt3N4 → Sn3N4 + ,3,Pt(NO2)4

Check :

3Sn reactant : Sn3 Product

(NO2)4 reactant : (NO2)4 product

Pt3 reactant : 3Pt product

N4 reactant : N4 product

Explanation:

Ammonia will decompose into nitrogen gas and hydrogen gas according to the following reaction. In that reaction 92 kJ will be absorbed.

2 NH₃ ----> N₂ + 3 H₂ ΔH = 92 kJ

Since the heat is absorbed, the sign is positive and we can add it to the reactants side.

2 NH₃ + 92 kJ ----> N₂ + 3 H₂

When 92 kJ are absorbed 34 g of ammonia are reacted. We can use that relationship to find the mass of ammonia that reacted when 184 kJ where absorbed.

34 g of NH₃ : 92 kJ

mass of NH₃ = 184 kJ * 34 g of NH₃/(92 kJ)

mass of NH₃ = 68 g

Answer: 68 g of ammonia were decomposed.

2 NH₃ ----> N₂ + 3 H₂ ΔH = 92 kJ

Step 1 - Understanding % concentration in mass

% concentration in mass expresses the concentration of a solute by its percentage, in mass, in relation to the total mass of the solution.

Mathematically, we can find this percentage by the following relation:

Step 2 - Caculating the % concentration for the given solution

According to the exercise:

Setting these values in the equation:

Answer: the % concentration of NaCl in this solution is 3.38%.

To answer this question, the first step is to convert the given number of molecules to moles using Avogadro's number:

Now, use the molecular weight of CO2 to find the mass of this amount of moles:

The mass of 5.32x10^22 molecules of CO2 is 3.872g.

The formed amount of KCl from the reaction is 297.12 g which is not enough to kill someone.

A limiting reagent can be defined as a reactant that is exhausted completely from the mixture at the completion of a chemical reaction.

When quantities of reactant are not taken in stoichiometry, the limiting reactants in the chemical reaction will decide the maximum amount of product.

Given, a balanced equation of the decomposition of KClO₃ is:

[tex]KClO_3\longrightarrow KCl +O_2[/tex]

One mole of KClO₃ will produce one mole of KCl.

122.55 g of the KClO₃ will produce KCl = 74.55 g

Given, the amount of KClO₃ = 488.43 g

Then 488.43 g of KClO₃ will produce KCl  = (74.55/122.55) × 488.43

                                                                      = 297.12 grams

As given 420.45g of potassium chloride would be required to kill someone. Therefore,  there is not enough potassium chloride that Melanie killed the butler.

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Answer:

Explanation:

Here, we want to know the number of molecules of oxygen that was reacted with

From the question, we can see that the mole ratio is 2 to 1

Thus, the number of molecules of oxygen reacted will be half that of hydrogen

Hence, the number of molecules of oxygen will be:

alkali metals has 6-p electrons

The alkali metals are elements of group 1 elements which are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).,

These elements are s-block elements because they have their outermost electron in an s-orbital.

The alkali metals are soft, shiny and highly reactive and  lose their outermost electron to create cations with charge +1, it can tarnish rapidly in the air due to oxidation by atmospheric moisture and oxygen.

Alkali metals are good conductors of heat and electricity, these elements are  specific, They are soft and can be cut by knife.

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Answer:

Balls uhhh neutron but if theres a better answer take it cuz im prolly wrong

Explanation:

50/50 im right up to you to take the chance or jus search it on tha goog

So,

The elements that belong to group 18 of the modern periodic table can be considered as some of the best electric insulators since they all contain completely filled valence shells and are, therefore, stable.

In general, elements that make good insulators are nonmetals, and these are located at the right of the periodic table. Thus the correct answer is B.

Answer

pH = 6

Explanation

Given that:

The concentration of the acid [H⁺] = 10⁻⁷ M

What to find:

The pH of the strong acid solution.

Step-by-step solution:

The pH of the strong acid solution whose concentration is 10⁻⁷ M can be calculated using the pH formula.

The pH formula is given by: pH = -log[H⁺]

Substitute [H⁺] as 10⁻⁷ M, we have:

pH = - log(10⁻⁷)

pH = -(-6)

pH = 6

The pH of the strong acid solution whose concentration is 10⁻⁷ M is 6.

6. As we can see from the graph, if we have only 100 grams of water, at 30°C, we will have 10 grams of KClO3 being dissolved in water, therefore if we have 300 grams of H2O, we will have 30 grams of KClO3 being dissolved at 30°C

7. The least soluble substance will be the one that shows up first in the temperature "line", if you follow the temperature up, the first solute that is listed will be considered to least soluble, therefore the least one will be KClO3

We must first determine the heat needed to heat 175mL of water. In the working temperature range we can assume that the density of water is 1g/mL, so the mass of water that we must heat will be 175g of water.

Now, the heat we need to heat that mass of water is calculated with the following equation:

Where Q is the heat required to heat the water

Cp is the specific heat of water equal to 4186 J/g°C

delta T is the change of temperature = 25°C-20°C=5°C

We replace the know values:

Now, to heat the water they tell us that the glucose combustion will take place. We must assume that all the heat generated in the reaction will go to heating the water and that there is no heat loss to the environment.

The combustion reaction of glucose generates 2538.7 kJ/mol. So the moles of glucose needed will be:

We calculate the grams of glucose by multiplying the moles by the molar mass of glucose equal to 180.2g/mol

grams of glucose= 1.44 mol x 180.2 g/mol=260g

Answer: To heat 175 mL of water from 20.0 °C to 25.0°C are required 260g of glucose

5s. Option D is correct

Electron orbitals are area around the nucleus where electron resides. The closer the orbital to the nucleus, the higher the energy level.

Based on the explanation above, 5s will be higher in energy than the 4d orbital.

Answer: By using Ideal gas law  PV=nRT  ,the final pressure is calculated

Explanation:

In thermodynamics a constant volume process is known as isochoric process and in this volume remains constant and pressure varies along with the temperature .

FORMULA USED - PV=nRT

If Volume is constant ,then  initial Temperature  = 18+273 = 291K

final temperature =225K

initial pressure = 0.90 atm

final pressure = ?

The final pressure comes out to be 0.6958 atm.

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0.029397 kCal

According to the question, we are to convert Joules to kCal

Using the conversion factor:

1 Joule = 0.000239 Kcal

Next is to convert 123 Joules to kCal

To do that, we will multiply 123 Joules with the factor as 0.000239

123 Joules = (0.000239 * 123) kcal

123 Joules = 0.029397 kCal

Hence the value of 123 joules is equal to 0.029397 kCal

Answer:

Explanation:

Here, we want to get the volume of NH3 that will react with 30L of NO at STP

From the question, we have it that 4 moles of ammonia reacted 6 moles of NO

Thus, we have the mole ratio as 6 to 4

Thus, the volume of ammonia reacted would be:

Explanation:

The % w/v s the number of grams of solute in 100 mL of solution

So it relates grams of solute with mL of solution.

Answer: B. grams and milliliters

The free energy of formation of the MgO is −597 kJ/mol.

We know that the free energy of formation is defined as the energy that is evolved or absorbed when a substance is formed from its components under standard conditions. In this case, we have that the magnesium and the oxygen are all pure substances.

It is important that we recall that the free energy of formation of a pure substance is zero. We have the free energy  of formation of the magnesium oxide as−597 kJ/mol.

Hence;

Sum of free energy of formation of products - Sum of free energy  of formation of reactants

We have;

(−597 kJ/mol) - (0  kJ/mol)

free energy of formation = −597 kJ/mol

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In order to properly balance an equation, we need to make sure that the same amount of elements on the reactants side matches the number of elements on the products side, we can do that by increasing the number in front of each molecule, the so called stoichiometric coefficient. In the reaction from the question we can properly balance by adding the following stoichiometric coefficients

For our question, we have:

2 Al + 3 Zn(NO3)3 -> 2 Al(NO3)3 + 3 Zn

Now this reaction is properly balanced

Al(NO3)3 has the coefficient 2

To solve this question, we need to know the molar mass of Ca. It is 40 g/mol

There are 3 atoms of Ca in Ca3(PO4)2

So the mass of Ca in Ca3(PO4)2 is 3x40 = 120 g

So:

375 grams ---- 100%

120 g --- x

x = 32%

Answer: 32% of calcium.