Answer:
right
Explanation:
How many copper atoms are in a pure copper statue with a mass of 187 kg?
Avogadro's number states that:
1 mol of Cu = 63.54 g of Cu = 6.02x10^23 atoms of Cu
Now, we proceed like this:
1 kg = 1000 g ===> 187 kg = 187,000 g
63.54 g Cu -------- 6.02x10^23 atoms of Cu
187,000 g Cu -------- X
X = 1.77x10^27 atoms Cu
Answer: 1.77x10^27 atoms Cu
If you add 8 g of salicylic acid to 84 g of an ointment base, what is the final concentration (w/w) of the product? Round to the nearest hundredths (w/w).Question 3 options:Answer will be in % nothing else! ACTIVE INGREDIENT will always be your numerator.NUMERATOR (ACTIVE INGREDIENT)--------------------------------DENOMINATOR (TOTAL) Numerator means the top part of your fractionThe (w/w) is telling you to divideSTEPS: Add 8 + 84 this will be your denominator totalthen multiply by 100 to add the % sign in #----- Divide = then multiply by 100 for the percent sign. What is your answer?#FINISH THE MATH FOR THE CORRECT ANSWER
Answer
Concentration = (8/92)*100 = 8.7%
Explanation
Given:
mass of salicylic acid (active ingredient) = 8 g
mass of an ointment base = 84 g
Required: concentration (w/w) of the product?
Solution:
Total mass of the mixture = 8 + 84 = 92 g
Concentration = (8/92)*100 = 8.7%
Write a balanced chemical reaction for each of the following double replacement reactions:
a. Hydrochloric acid reacts with sodium hydroxide.
b. Hydrochloric acid reacts with barium hydroxide.
c. Hydrochloric acid reacts with ammonium hydroxide
Balanced chemical reaction for each of the following double replacement reactions:
a) HCl + NaOH -----> NaCl + H₂O
b) 2HCl + Ba(OH)₂ ----> BaCl₂ + 2H₂O
c) 3HCl + Al(OH)₃ ----> AlCl₃ + 3H₂O
Balanced chemical reaction is when the number of atoms in the reactant sides are equal to the no. of atoms in product side.
a) Hydrochloric acid reacts with sodium hydroxide.
HCl + NaOH -----> NaCl + H₂O
b) Hydrochloric acid reacts with barium hydroxide.
2HCl + Ba(OH)₂ ----> BaCl₂ + 2H₂O
c) Hydrochloric acid reacts with ammonium hydroxide
3HCl + Al(OH)₃ ----> AlCl₃ + 3H₂O
Thus, Balanced chemical reaction for each of the following double replacement reactions:
a) HCl + NaOH -----> NaCl + H₂O
b) 2HCl + Ba(OH)₂ ----> BaCl₂ + 2H₂O
c) 3HCl + Al(OH)₃ ----> AlCl₃ + 3H₂O
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A certain copper ore contains 3.24% of Cu2S by mass. In 1991, a single open-air smelt furnace heated 30000 tons of this ore. Compute the mass of copper metal obtained by this process. Enter in tons.
The mass of the copper that is obtained is 97.2 tons.
What is combustion?We can define the term combustion as the procedure by which a substance can be burnt in oxygen. We can also be able to refer to the process as roasting the object in the air. It is an oxidation reaction.
Having said all all of these, the reaction equation can be written as;
[tex]Cu_{2} S + O_{2} ------ > 2Cu + SO_{2}[/tex]
We know that the percent of the copper that it contains can now be used when we are trying to compute the mass of the copper that can be obtained from the process as we are going to have in the question that is at hand here to solve.
We are now going to proceed to see the mass of the copper that can be produced from the 300 tons of the copper I sulfide ore given.
Thus;
The mass of copper that can be obtained is;
3.24/100 * 3000 tons
= 97.2 tons
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Which type of radiation would you consider ionizing radiation?MicrowavesVisible lightSound wavesGamma rays
Ionization radiation is a type of energy with such a high value that it is capable of removing electrons from atoms and converting them into ions. This type of energy is extremely dangerous. The types of energy that fall into this category are X-rays and gamma rays.
So, the answer will be Gamma rays
Please help
For this assignment, you will create a public service
announcement, or a PSA, describing the environmental
and economical impact of the end-products of
chemical reactions of those that may result in the
greenhouse effect or ozone depletion.
Items you must include or address:
• describe the chemical reaction
occurring using a
chemical equation and identifying the reactants
and products.
• demonstrate how mass/matter is conserved
during this chemical reaction.
• describe the energy changes that accompany this
chemical reaction.
• describe how the end-products affect the
environment.
• describe the economical impact.
provide ways for anyone to help reduce the
environmental impacts.
I need to be a letter to your senator
The assignment about the Public Service Announcement (PSA) describing the environmental impacts due to ozone depletion and the greenhouse effect is given below.
Since we live in a modern industrialized world, we need to get exposed to lots of chemicals and pollutants. With modernization people began to use Air conditioners, Refrigerants, and other household appliances for a sophisticated lifestyle without knowing the harmful effects it causes on the environment.
The use of Refrigerators and Air Conditioners contains Freons which are used as aerosol propellants. These freons release CFCs which are called as Chloro-Fluro-Carbons which are the main element responsible for damaging the environment by causing both global warming and Ozone depletion.
The Chlorine atom that is released from the CFCs breaks the bond of the Ozone. The reaction is elucidated below:
ClO + O -------> Cl + O₂
This breaks the bond of Ozone creating Ozone depletion and eventually leading to Global Warming.
Similar to Ozone depletion, another main environmental problem is the greenhouse effect which is occurring mainly due to the release of harmful gases from automobiles, and industries such as CO₂, SO₂, etc... These gases absorb and trap the solar heat from the Infrared region and creates a greenhouse effect. These gases are called greenhouse gases.
This greenhouse effect, ozone depletion eventually leads to an increase in global temperature and results in the rising of sea levels by melting the glaciers and icebergs. The climatic pattern is adversely affected. This would affect agriculture, as well as the health of humans as harmful UV rays that enter the earth due to ozone depletion, will lead to skin diseases, cancer, and so on.
By adversely affecting the agriculture and health of the world, there would be a drop in the entire economy as our country is dependent mainly on agriculture for the nation's economy.
The effects of these could be minimized by using public transport, planting trees, using refrigerators and air conditioners free from freons, and proper treatment of the wastes eliminated from industries must be ensured.
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Write down a specific step by step procedure of the titration process which the goal is to determine the unknown concentration of a basic solution.
Explanation:
Titration is a technique used to determine the amount of matter in a sample using a solution of known concentration. In other words, titration is a quantitative chemical analysis. In this process, the sample has its concentration determined through a chemical reaction when it is mixed with another substance. The use of pH indicators in this process is useful to determine the endpoint of the titration, indicating that the entire sample has reacted. Titration is used to accurately determine the amount of a substance, confirm that the concentration described on the label is true or that the amount of a chemical compound is indicated on the package.
Sample weighing: With the solid sample on a watch glass, weigh it on the balance.
Sample dissolution: The sample is transferred to an Erlenmeyer flask with water, where dissolution takes place.
Problem solution: The solution is transferred to a volumetric flask and the volume is made up with water, creating the problem solution.
Aliquot transfer: Remove an aliquot of the problem solution with the aid of a pipette and transfer it to an Erlenmeyer flask.
Titration: To the Erlenmeyer flask, the problem solution (titrated) is added and the solution of known concentration (titrant) is inserted into the burette.
An acid-base indicator is also added to the titrator to indicate when the titration should be stopped due to the color change. The color change indicates the end point or turning point of the titration.
After that, when the color change persists, the volume of titrant used is verified and stoichiometric calculations will help us to discover the concentration of the titrated solution.
Answer:
Step 1 - Sample weighing: With the solid sample on a watch glass, weigh it on the balance.
Step 2 - Sample dissolution: The sample is transferred to an Erlenmeyer flask with water, where dissolution takes place.
Step 3 - Problem solution: The solution is transferred to a volumetric flask and the volume is made up with water, creating the problem solution.
Step 4 - Aliquot transfer: Remove an aliquot of the problem solution with the aid of a pipette and transfer it to an Erlenmeyer flask.
Step 5 - Titration: To the Erlenmeyer flask, the problem solution (titrated - basic solution) is added and the solution of known concentration (titrant - acidic solution) is inserted into the burette.
Step 6 - An acid-base indicator is also added to the titrator to indicate when the titration should be stopped due to the color change. The color change indicates the endpoint or turning point of the titration.
Step 7 - After that, when the color change persists, the volume of titrant used is verified and stoichiometric calculations will help us to discover the concentration of the titrated solution.
Classify each of the following chemical reactions as a synthesis decomposition and single displacement or double displacement reaction
1. Synthesis reaction : there is only 1 product formed from 2 or more reactant
E.g:
[tex]H_2(g)+N_2(g)\text{ }\Rightarrow2NH_3(g)\text{ }[/tex]2. Decomposition : reaction that occurs in presence of UV light and only 1 reactant that decomposes into 2 or more products.
E.g:
[tex]CH_3Br(g)+UV_{light}\Rightarrow CH_3(g)\text{ + Br (g)}[/tex]3. Single displacement : reaction that occurs when 1 reactant displaces other reactant from its compound:
E.g:
[tex]Zn(s)+CoCl_2(aq)\text{ }\Rightarrow ZnCl_2(aq)\text{ + Co(s)}[/tex]4. Double displacement : reaction that occurs when both reactant displaces each other.
E.g :
[tex]K_2S(aq)+Co(NO_3)_2\Rightarrow2KNO_3(aq)\text{ + }CoS(s)\text{ }[/tex]Which of the following elements would have chemical properties similar to those of Na?O Ne KBr
Ne is a noble gas, O is a non metal and Br is an halogen.
K is a metal that belongs to the same group as Na, it means that they have similar chemical properties.
It means that the answer is K.
the partial negative charge at one end of a water molecule is attracted to the partial positive charge of another water molecule. what is this attraction called?
Hydrogen bonding is formed when the partial negative charge at one end of a water molecule is attracted to the partial positive charge of another water molecule
Hydrogen bonding is a potent intermolecular force. In a water molecule, a partial negative charge is formed due to the oxygen, which is electro-negative.This oxygen gets attracted towards the positively charged Hydrogen, thus partial charges are shared between these two atoms of two different molecules.An electrostatic force is created between these molecules which helps in attraction of the partial charges.A hydrogen bond is formed between the water molecules which is formed due to hydrogen bonding. This kind of bond is formed between hydrogen atom and an electronegative atom, typically fluorine (F), nitrogen (N), or oxygen (O).Thus, when the partial negative charge at one end of a water molecule is attracted to the partial positive charge of another water molecule, hydrogen bonding is formed.
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identify an element that has similar chemical properties as those of the element krypton (K).
I believe the incorrect statement is dissolution of oxygen in water is due to dipole- induced dipole interaction.
For this question we have 4 options and relates a few chemical concepts, let's analyze each option and reach a final conclusion:
A. Since in a geometric 3-D point of view, neopentane is more closely together in its bondings, the boiling point will be lower in it, and n-pentane has more surface to be heated, therefore the boiling and melting point will be higher, as it is proven experimentally, n-pentane = 36.1°C, neopentane = 9.5°C. Correct
B. If we have O2 being thrown in water, the covalent bonding between these two atoms is very nonpolar and weak, the weak Van der Waals force, also known as temporary dipole-induced dipole interactions. Correct
C. Dipole moment has a lot to do with the strength of a bond, greater the dipole moment, the stronger the bond will be, and if we have a strong bond, more energy will be required to break, therefore higher the boiling and melting point will be for these compounds, therefore this one is Incorrect
D. Yes, in DNA the main type of intermolecular force is Hydrogen bonding
Many people use a microwave oven to cook their food. When it is turned on, what type of energy transfer is taking place?A. Electrical to chemicalB. Nuclear to heatC. Electromagnetic to soundD. Electrical to electromagnetic
Explanation:
The microwave receives, from a transformer (energy source), a fixed voltage and generates, through the vibration of electrons in its resonant cavities, electromagnetic waves inside the device.
Answer: D. Electrical to electromagnetic
25.0 mL of a solution with concentration 0.30 M is diluted to a final volume of 150. mL. What is the final concentration?
Answer: the concentration of the solution after the dllution is 0.050 M
Explanation:
The question requires us to determine the concentration of a solution after a dilution process.
The following information was provided by the question:
Concentration of initial solution = C1 = 0.30 M
Volume taken from initial solution = V1 = 25.0 mL
Volume of final solution = V2 = 150 mL
When a solution is diluted, the number of moles of the substance remains the same. Thus, we can say that:
[tex]n_1=n_2[/tex]where (1) is the solution before dilution and (2) refers to the solution after dilution.
The number of moles of a substance can be obtained from the definition of molarity (or molar concentration), where the number of moles is divided by the volume of the solution:
[tex]molarity=\frac{number\text{ of moles}}{volume}\rightarrow number\text{ of moles = molarity}\times volume\rightarrow n=C\times V[/tex]Thus, we can write that for a dillution:
[tex]n_1=n_2\rightarrow C_1\times V_1=C_2\times V_2[/tex]From the expression above we can determine the concentration of the final solution. Applying the values provided by the question to the expression above, we'll have:
[tex]\begin{gathered} \begin{equation*} C_1\times V_1=C_2\times V_2 \end{equation*} \\ \\ (0.30M)\times(25.0mL)=C_2\times(150mL) \\ \\ C_2=\frac{(0.30M)\times(25.0mL)}{(150mL)}=0.050M \end{gathered}[/tex]Therefore, the concentration of the solution after the dilution is 0.050 M.
Calculate the mass (in g) of 5.86x10^20 SO3 molecules.
Answer
0.0779 g SO₃
Procedure
To solve this question, you will need to use the Avogadro's number equivalent to 6.02214 x 10^23 molecules/ mol, and then the molecular weight in grams per mole for the SO₃.
[tex]5.86\times10^{20}\text{ molecules SO}_3\frac{1\text{ mol SO}_3}{6.02214\text{ x 10}^{23}\text{molecules SO}_3}\frac{80.06\text{ g SO}_3}{1\text{ mol SO}_3}=0.0779\text{ g SO}_3[/tex]3.(a) Draw the following five-carbon hydrocarbons:•Pentane•Pentene•Pentyne(e)Classify each molecule and explain the differences between them. (Classes of organic molecules include alkanes, alkenes, alkynes, alcohols, carboxylic acids, aldehydes, ketones, esters, ethers, amines, and amides.)
Structural formulas are ways atoms and elements are arranged in a molecule. The structural formula of pentane, pentene, and pentyne are as shown below;
Pentane - C5H12
Pentene - C5H10
Pentyne - C5H8
e) Pentane is an alkane compound with a general formula CnH2n+2. The chemical formula of pentane is C5H12. There are only single bonds between the C-H atoms in the molecule.
Pentene is an alkene compound with a general formula of CnH2n. The chemical formula of pentene is C5H10. There is a double bond present between the C=H atoms. This double bond shows that the compound is an alkene.
Pentyne is an alkyne compound with a general formula of CnH2n-2. The chemical formula of pentene is C5H8. There is a triple bond present between the Carbon Hydrogen atoms. This presence of a triple bond shows that the molecule is an alkyne compound.
How much heat is released when 245 g of steam cools from 106.0°C to -4.5°C
ANSWER
The amount of heat released is -54, 957.175J
EXPLANATION
Given that;
[tex]\begin{gathered} \text{ The mass of the steam is 245g} \\ \text{ The final temperature of the steam is -4.5}\degree C \\ \text{ The initial temperature of the steam is 106.0}\degree C \end{gathered}[/tex]To find the amount of energy released, then apply the below formula
[tex]\text{ q = mc \lparen}\theta2\text{ - }\theta1)[/tex]Recall, that the specific heat capacity of steam (c) is 2.03 J/g degrees Celcius
[tex]\begin{gathered} \text{ q = 245 }\times\text{ 2.03 \lparen-4.5 - 106\rparen} \\ \text{ q = 245 }\times\text{ 2.03 \lparen -110.5\rparen} \\ \text{ q = -54,957.175J} \end{gathered}[/tex]Therefore, the amount of heat released is -54, 957.175J
How many liters of NH3, at STP, will react with 5.3 g. O2 to form NO3 and water? 4NH3 (g) + 9O2 (g) —> 4NO3 + 6H2O (g)
Step 1
The reaction must be completed and balanced:
4NH3 (g) + 9O2 (g) => 4NO3 + 6H2O (g)
Reactants: NH3 and O2
Products: NO3 and H2O
--------------------
Step 2
Information provided:
STP conditions, therefore:
1 mole of gas (NH3 in this case) = 22.4 L (volume)
5.3 g of O2
Liters => L
Grams => g
---------
Information needed:
The molar mass of O2 = 32.0 g/mol
-------------------
Step 3
By stoichiometry,
1 mole NH3 = 22.4 L NH3
1 mole O2 = 32.0 g O2
Procedure: We will work with volume and mass
4NH3 (g) + 9O2 (g) => 4NO3 + 6H2O (g)
4 x 22.4 L NH3 ---------- 9 x 32.0 g O2
X ----------- 5.3 g O2
X = 5.3 g O2 x 4 x 22.4 L NH3/9 x 32.0 g O2 = 1.65 L approx.
Answer: 1.65 L of NH3
How many moles of magnesium is 5.01 x 10^22 atoms of magnesium?
The question requires us to calculate the number of moles that corresponds to 5.01 x 10^22 atoms of magnesium.
To solve this question, we'll need to use the Avogadro constant. This number, defined as 6.02 x 10^23, relates the number of constituent particles (molecules, atoms or ions, for example) in a sample with the amount of substance in that sample. We can use it by saying that 1 mol of a substance corresponds to 6.02 x 10^23 constituent particles of this substance.
Then, using the information above, we can calculate the number of moles in 5.01 x 10^22 atoms of magnesium (Mg):
6.02 x 10^23 atoms of Mg --------------- 1 mol of Mg
5.01 x 10^22 atoms of Mg ---------------- x
Solving for x, we'll have:
[tex]x=\frac{(5.01\times10^{22}\text{ atoms of Mg)}\times(1\text{ mol of Mg)}}{(6.02\times10^{23}\text{ atoms of Mg)}}=0.0832\text{ mol of Mg}[/tex]Therefore, 5.01 x 10^22 atoms of magnesium corresponds to 0.0832 mol of this element.
Which phase change is endothermic?
A) H₂O(t)→ H₂O(g)
B) I2(g) → I2(s)
C) Hg(t)→ Hg(s)
D) H₂S(g) → H₂S(t)
Scientists discovered a rock formation in the mountains that
contains some amount of Uranium-235. Upon further testing you
learn that the rock is composed of 25% Uranium-235. Knowing that
the rock is 1.426 billion years old, how long is the half-life of
Uranium-235?
The half-life of the Uranium-235, given that the rock is composed of 25% Uranium-235 is 713 million years
How do i determine the half-life?First, we shall calculate the number of half lives that has elapsed. This can be obtained as follow:
Original amount of Uranium-235 (N₀) = 100%Amount remaining of Uranium-235 (N) = 25%Number of half-lives (n) =?2ⁿ = N₀ / N
2ⁿ = 100 / 25
2ⁿ = 4
2ⁿ = 2²
n = 2
Finally, we shall determine the half-life of the Uranium-235. This can be obtained as follow:
Number of half-lives (n) = 2 Age of rock (t) = 1.426 billion years Half-life (t½) = ?n = t / t½
Cross multiply
n × t½ = t
Divide both sides by n
t½ = t / n
t½ = 1.426 / 2
t½ = 713 million years
From the calculations made above, we can conclude that the half-life is 713 million years
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A reaction take place between an acid and 0.5 grams of powdered magnesium. Which statement is true?A. The powdered magnesium reacts faster because the activation energy has been lowered.B. The magnesium tracts reacts faster because It has a higher concentration of magnesium.C. The powdered magnesium react faster because it has a greater surface area.D. The magnesium react faster it will create a higher temperature once the reaction starts
Explanation:
The rate of a reaction is defined as the rate of disappearance of reactants in a reaction or the rate of conversion of appearance of products during a reaction.
The rate of a reaction depends on the concentration of the reactants, the temperature of the reaction, the nature of reactants, and the presence or absence of catalysts during the reaction.
The surface of reactants comes into play. Reactants with high surface areas react faster than reactants with fewer surface areas. Hence, powdery reactants react faster than solid reactants.
Answer: C. The powdered magnesium react faster because it has a greater surface area.
does lead melt in atoms or molecules
Answer:
Atoms
Explanation:
Answer:
atoms
Explanation:
its right, trust
Which of these are true situations that could be explained by the kinetic molecular theory?Select all that apply.
Kinect-molecular theory hypothesis:
- The formation of a gas occurs by a large number of molecules;
- Gas molecules have a negligible dimension, which means that the volume occupied by them is very small, almost insignificant;
- These gases move in a discontinuous and random way, thus occupying the entire volume of the container where they are found, having a rectilinear and uniformly varied movement;
- They are independent, they only interact with each other when a collision occurs;
- Collisions between molecules and molecules and between molecules and container walls are elastic collisions, which cause the kinetic energy of the molecules to remain constant.
Having seen these statements, the answers can only be:
The warmer a glass of water, the faster a drop of ink will spread through the water.
The colder a room is, the longer it would take to smell a spray of perfume from the other side of the room.
Predict the nature of the indicated
covalent bond.
H-C=N:
polar
non-polar
Answer:
I would say Polar
Explanation:
Aluminum reacts with chlorine gas to form aluminum chloride. (a) If 35g of aluminum reacts with excess chlorine, how many grams of aluminum chloride will form. (b) How many grams of chlorine will react completely with 42.8 g of aluminum 2Al + 3Cl2 ==> 2AlCl3
Answer
(a) 172.848 grams
(b) 168.584 grams
Explanation
The balanced equation for the reaction of aluminum with chlorine gas is:
[tex]2Al+3Cl_2\rightarrow2AlCl_3[/tex](a) Mass of Al = 35 g
From the Periodic Table;
Molar mass of Al = 27 g/mol
Molar mass of AlCl₃ = 133.34 g/mol
From the balanced equation above; 2 moles Al produced 2 moles AlCl₃
So in grams, 2 mol x 27 g/mol = 54 g Al produced 2 mol x 133.34 g/mol = 266.68 g AlCl₃
Therefore, 35 g Al will form:
[tex]\frac{266.68\text{ g AlCl}_{3}\text{ }\times35\text{ g Al}}{54\text{ g Al}}=172.848\text{ g AlCl}_{3}[/tex]172.848 grams of aluminum chloride will be formed.
(b) Mass of Al = 42.8 g
Also from the Periodic Table; the molar mass of Cl₂ = 70.90 g/mol
From the equation above; 2 mol of Al requires 3 mol Cl₂.
In grams, 2 mol x 27 g/mol = 54 g Al requires 3 mol x 70.90 g/mol = 212.7 g Cl₂
Hence, 42.8 g Al will react with:
[tex]\frac{42.8\text{ g Al }\times212.7\text{ g Cl}_{2}}{54\text{ g Al}}=168.584\text{ g Cl}_{2}[/tex]168.584 grams of chlorine will react completely with 42.8 g of aluminum
A 695.7 ng sample of an unknown radioactive substance was placed in storage and its mass measured periodically. After 47 daysthe amount of radioactive substance had decreased to 86.96 ng. How many half-lives of the unknown radioactive substancehave occurred?
The decay of this radioactive unknown compound is a first-order process.
We can express the time dependence of its mass m using a first-order integrated rate law, where k is the rate constant:
[tex]m_t=m_0xe^{-kxt}[/tex]mt = mass at time t
m0 = initial mass
t = time
-----------------------------------------------------------------------------------------------------
Procedure:
1) We need to find "k":
From the first-order rate law we clear k,
[tex]\begin{gathered} \frac{m_t}{m_0}=\text{ }e^{-kxt} \\ \ln (\frac{m_t}{m_0})=\text{ -kxt} \\ \frac{\ln (\frac{m_t}{m_0})}{-t}=\text{ k} \end{gathered}[/tex][tex]k\text{ = }\frac{\ln (\frac{86.96ng}{695.7ng})}{-47}=0.044days^{-1}\text{ }[/tex]----------------------------------------------------------------------------------------------
2) We find the half-life from the value of k we have just calculated:
[tex]t_{\frac{1}{2}}=\text{ }\frac{\ln 2}{k}=\text{ }15.7\text{ days}[/tex]-----------------------------------------------------------------------------------------------
3) The number of half-lives of the unknown sample is:
Number of Half-lives = 47 days / 15.7 days = 3 (approx.)
Answer: Number of half-lives = 3
Electrons in atoms exist in particular energy levels. A _______ must be emitted or absorbed to move between energy levels.Question 19 options:A) photonB) electronC) particleD) quantum
Answer: We can complete the sentence as:
"Electrons in atoms exist in particular energy levels. A photon must be emitted or absorbed to move between energy levels" (letter A).
Explanation:
The question requires us to choose the best option to complete the sentence: "A ________________ must be emitted or absorbed to move between energy levels".
Energy levels are fixed distances from the nucleus of an atom where electrons can be found. Energy levels can be compared to stairs in a staircase: we can stand on a step, on the previous step or the next step, but never between them; this is what happens to electrons, as they can occupy one energy level or another but not the space between energy levels.
To move from one energy level to another, an electron must absorb energy (to move to a higher level) or emit energy (to move to a lower level). The energy difference between a lower starting level and a higher ending level must correspond to the energy of a photon of light absorbed in order to make the transition between energy levels possible. Additionally, electrons are usually unstable at excited states (when at a higher energy level that it was initially), and the electron quickly returns to the lower energy level emitting the excess of energy in the form of light (as a photon of light).
Therefore, considering the information above, we can complete the sentence as:
"Electrons in atoms exist in particular energy levels. A photon must be emitted or absorbed to move between energy levels" (letter A).
70.0 mL of water was added to 100.0 mL of 0.250 M CaCl₂ solution. Assuming the volumes are additive, what is the CaCl₂ concentration in the diluted solution?
70.0 mL of water was added to 100.0 mL of 0.250 M CaCl₂ solution. Assuming the volumes are additive, The CaCl₂ concentration in the diluted solution is 0.147 M.
given that :
volume V1 = 100 mL
volume V2 = 100 + 70 = 170 mL
Molarity M1 = 0.250 M
Molarity M2 = ?
using dilution equation we get :
M1 V1 = M2 V2
M2 = ( M1 V1) / V2
M2 = ( 0.250 × 100 ) / 170
M2 = 0.147 M
Therefore , the dilution solution will have 0.147 M
Thus, 70.0 mL of water was added to 100.0 mL of 0.250 M CaCl₂ solution. Assuming the volumes are additive, what is the CaCl₂ concentration in the diluted solution is 0.147 M.
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How many liters of a 0.75 M solution can be made with 75 grams of lead (ll) oxide?
Step 1
Molarity is defined as:
Molarity (M or mol/L) = Moles of lead (II) oxide/Volume of solution (L)
Molarity = mass of lead (II) oxide/molar mass of lead (II) oxide x volume (L) (1)
-------------------------
Step 2
The molar mass of PbO = 223 g/mol
PbO = lead (ll) oxide
------------------------
Step 3
Data provided:
Molarity = 0.75 M
Mass of PbO = 75 g
------------------------
Step 4
Procedure:
The volume of the solution is cleared from (1):
Volume (L) = mass PbO/(molar mass PbO x Molarity)
Volume (L) = 75 g/(223 g/mol x 0.75 mol/L) = 0.45 L approx.
Answer: Volume = 0.45 L