4. What is the percent by mass of tungsten in the calcium tungstate compound CaWO3, commonly
called scheelite?
Answer: 67.4%
Explanation:
Ca 40.8
W. 183.8
O. 16.00
CaWO3 272.6
W = 183.8/272.6 = 0.674
67.4% percent by mass of tungsten in the calcium tungstate compound CaWO3, commonly called scheelite.
What are calcium tungstate screens?The 200 Speed Blue Emitting Calcium Tungstate Screen is the most commonly used Non-Rare Earth intensifying screen. With a faster speed than Detail or Medium speed screens, the Hi-Plus Intensifying Screen provides an efficient balance between the time patients are exposed during x-rays and image quality and detail.
Who introduced calcium tungstate?It was also used in radium paint in the same fashion as was zinc sulfide, and Thomas Edison invented a fluoroscope with a calcium tungstate-coated screen, making the images six times brighter than those with barium platinocyanide; the latter chemical allowed Röntgen to discover X-rays in early November 1895.
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How many molecules are there in 42gms of Na?
According to bond energy tables, the triple bond of N2 is 946 kJ/mol while the bond of I2 is 151 kJ/mol. Based on simple chemical ideas about what molecular properties lead to activation energies, it is reasonable to expect that the reaction of H with N2 will have a higher activation energy than the reaction of H with I2.
1. Yes, I2 is heavier than N2.
2. No, bond energies do not matter much; lone pairs are crucial.
3. Yes, in both cases the reactant bond must be stretched by collisions and more energy is required for the stronger bond.
4. Yes, in both cases the reactant bond must be broken before the H can bond.
5. No, activation energies have nothing to do with bond energies.
Answer:
Yes, in both cases the reactant bond must be broken before the H can bond.
Explanation:
Let us remind ourselves of the basics of the collision theory. According to this theory, chemical reaction occurs because of the collision of particles of substances in a chemical reaction system.
This means that the bond between reactants must first be broken and new bonds formed in products. Activation energy is the minimum energy required for a reaction to occur. This energy goes into the rearrangement of reactant bonds to enable them to recombine and form products.
Since the N2 bond energy is far higher than the I2 bond energy, a greater degree of energy is needed overcome the energy barrier in the reaction of H2 with N2 compared to the reaction of H2 and I2 . Therefore, the activation energy for the reaction of H2 and N2 is much higher than the activation energy for the reaction of H2 with I2.
which section from the article most emphasizes the role of technological development in the discovery of cells
Answer:
B. The microscope paved the way
Explanation:
This section from the article, "History of the Cell: Discovering the Cell", that emphasizes the role of technological development in the discovery of cells, is the subheading, "The microscope paved the way". In this subheading, the author narrated how Robert Hooke improved the existing microscope, and was able to discover the cell through it.
Further improvement of the simple microscope by Antonie van Leeuwenhoek led to the discovery of bacteria and protozoa.
WORTH 40 POINTS HELLPPPP
What class of element is Astatine (At)?
Answer:
halogen.
nonmetal.
Explanation:
What is the function of the chloroplast? A. Breaks down sugar to make energy B. To hold the cell together C. To make animals green D. Uses sunlight to create glucose (sugar)
Answer:
D. Uses sunlight to create glucose (sugar)
Explanation:
The function of the chloroplast is that it uses sunlight to create glucose.
The chloroplast allows for light to be trapped which is used for the synthesis of glucose from carbon dioxide and water.
The chloroplast is a rich in a pigment called the chlorophyll. This chlorophyll is a green pigment which allows for the trapping of solar energy
This solar energy is used to carryout the photosynthetic reaction.
Why is this image a good model for the Law of Conservation of Mass?
Answer:
The Law of Conservation of Mass states that mass is neither created nor destroyed in chemical reactions. Since the number and type of atoms in the reactant side of the chemical equation are the same as on the product side, the Law of Conservation of Mass has been demonstrated.
Explanation:
In the answer.
The two main postulates that was given by Antoine Lavoisier are, oxygen play an important role in combustion and the other is mass of the reactant and product is conserved. Therefore, the given image is a good model for the Law of Conservation of Mass.
What is law of conservation of mass?According to Law of conservation of mass, mass can neither be created nor be destroyed. Mass can only be transformed from one form to another. The law of conservation of mass was given by Antoine Lavoisier.
Every reaction in nature follow the law given by Antoine Lavoisier that is mass is always conserved. Another postulated that was given by Antoine Lavoisier is the role of oxygen in combustion reaction. Combustion can not happen without presence of oxygen.
The image is a good model for the Law of Conservation of Mass as number and type of atoms on the reactant side and product side are the same.
Therefore, the given image is a good model for the Law of Conservation of Mass.
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Match each term to its description. (3 points)
Excess reactant
Theoretical Yield
Limiting Reactant
1. Reactant that can produce more of
the product
2. Reactant that can produce a lesser
amount of the product
3. Amount of product predicted to be
produced by the given reactants
Answer:
1. B 2. C 3. A
Explanation:
I just took it
Limiting reactant is the reactant the produces the least amount of the product.
In a chemical reaction, the reactant that is in least supply is the limiting reactant while the reactant that is more than required is the excess reactant.
To match each term with its description, we have;
Excess reactant - Reactant that can produce more ofthe product
Limiting Reactant - Reactant that can produce a lesseramount of the product
Theoretical Yield - Amount of product predicted to beproduced by the given reactants
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The octet rule states that atoms in molecules share electrons in such a way that each atom has a full valence shell. Determine whether each structure has the correct number of electrons and obeys the octet rule. Classify structures that have the correct number of electrons and obey the octet rule as valid, and those that do not as invalid. valid structure invalid structure
Answer:
Their must be a picture with this question so we can answer it
Explanation:
According to octet rule the bonded valence shells are completely filled. All the compounds except the first one, CH₃CH₃O is invalid since H does not obey the rule and invalid.
What is octet rule?Octet rule says that an atoms become stable when it completes its valence shell to 8 electrons or 2 electrons for K-shell. Thus bonded shells have to completely filled to be stable.
Each atom shares its electrons based on its valency. For example carbon have a valency of 4 and it forms for bonds and oxygen and sulfur have two and hydrogen forms only one bonds.
In the first compounds CH₃CH₃O, where one H forms two bonds which is not possible and invalid.
In the second compound CONH, all the atoms satisfies its valency including nitrogen having a valency of three forms three bonds. Similarly in CH₂F₂, one fluorine forms one bond and the structure is valid.
In the case of Br₂ , each bromine shares one electron with the other and complete their octet to eight electrons. In NH₃, SCO and COCl₂ all the atoms satisfies their valency and the structures are valid.
Therefore the only invalid structure is first compound, remaining all are valid.
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Your question is incomplete. But most probably your complete question was as in the uploaded image.
Which of the following statements about semi-empirical methods are true: It can be used for static molecules but not for reactions in which bonds are forming or breaking. It combines a theoretically sound model of bonding with some experimentally determined parameters. It can determine precisely both the location and the energy of bonding electrons. It is good at predicting structural properties that arise from subtle interactions of orbitals.
Answer:
The true statement about semi-empirical methods is:
It combines a theoretically sound model of bonding with some experimentally determined parameters.
Explanation:
Semi-empirical methods are theoretical assumptions combined with experimental data to improve computational performance. In modern computational chemistry, semi-empirical methods play important roles. The methods offer the advantage of a substantial reduction in computational time. They also increase one's ability to carry out calculations for large molecules. However, with these methods, there is the added loss of the variational principle because one can obtain a total energy that is below the true total energy. Again, semi-empirical methods have limited applicability because the methods apply to molecules with parameterized elements. Semi-empirical methods may supply spurious results, especially since the molecular systems may be different from those used for parameterizations.
What is the maximum mass of ammonia (NH3) that can be produced from the synthesis reaction of 781 g of nitrogen and 656 g hydrogen?
HINT: You will need to write a balanced chemical equation and perform 2 calculations before you can determine the answers.
How many moles of phosphoric acid would be needed to produce 15 grams of water?
Moles of phosphoric acid would be needed : 0.833
Further explanationGiven
15 grams of water
Required
moles of phosphoric acid
Solution
Reaction(decomposition) :
H3PO4 -> H2O + HPO3
mol water (H2O :
= mass : MW
= 15 g : 18 g/mol
= 0.833
From the equation, mol ratio H3PO4 = mol H2O = 1 : 1, so mol H3PO4 = 0.833
A brown dye has a percent composition of 62.41% C, 5.24% H, and 32.36% N by mass with a molar mass of 346.40 g/mol. Determine the molecular formula of the dye
The molecular formula : C₁₈H₁₈N₈
Further explanationGiven
62.41% C, 5.24% H, and 32.36% N
Required
The molecular formula
Solution
mol ratio
C : 62.41/12.0096 = 5.1967
H : 5.24/1.00784 = 5.1992
N : 32.36/14.0067 = 2.310
Divide by 2.310(smallest)
C : 5.1967/2.31=2.25
H : 5.1992/2.31 = 2.25
N : 2.31/2.31 = 1
Multiplied by 4
C : H : N = 9 : 9 : 4
The empirical formula : C₉H₉N₄
(C₉H₉N₄)n=346.40 g/mol
(12.0096 x 9 + 1.00784 x 9 + 14.0067 x 4)n=346.4
(108.0864+9.07056+56.0268)n=346.4
(173.184)n=346.4
n=2
The molecular formula : C₁₈H₁₈N₈
A chemist has a block of copper metal (density is 8.96). They drop the metal into a graduated cylinder containing water, and find the volume change is 2.90 mL. What is the mass of the block , in grams?
Answer:
26g
Explanation:
Given parameters:
Density = 8.96g/cm³
Volume of metal = 2.9mL
Since 1mL = 1cm³;
Volume = 2.9cm³
Unknown:
Mass of the blocks in grams = ?
Solution:
Density is the mass per unit volume of a substance;
Mass = density x volume = 8.96 x 2.9 = 26g
Which of the following choices is not evidence supporting the theory of plate tectonics?
Answer:
B
Explanation:
An early version of the Periodic Table had the elements listed in order of increasing relative atomic
mass instead of increasing atomic number. Doing so today would result in the reordering of three
pairs of elements in the first five periods. Identify the three element-pairs.
Answer:
Although he was unaware ofit, Mendeleev had actually placed the elements inorder of increasing “atomic number,” a numberrepresenting the amount of positively charged protons in the atom (also thenumber of negatively charged electronsthat orbit the atom). Mendeleev went even further.
definition of solubility
(science)
Answer:
th relative ability of a solute to devolve into a solvent
Why reaction of lead with dilute acid Cannot liberate hydrogen
Answer:
Copper does not reacts with dilute sulphuric acid, liberating hydrogen because copper is lower in the electromotive series than hydrogen. ... The metals above hydrogen in the activity series react with dilute sulphuric acid and dilute hydrochloric acid to liberate hydrogen.
What is the difference between stored energy and usable energy
answer:
In biology, the energy that is stored in the bonds between compounds is termed as the chemical energy. This chemical energy is released and converted into different forms according to the functions of the body.
Potential energy can be described as the energy that is stored in an object. In physics, the energy that an object possesses while at rest is termed as the potential energy.
The energy that can be used during work is termed as the kinetic energy. In physics, kinetic energy can be described as the energy that an object possesses while in motion.
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Answer: The stored energy is termed as potential energy while the working energy is termed as kinetic energy. The electricity used in our homes is also a form of energy because it is a form of usable power. The places from which the different energies are obtained are known as energy sources.
Write a balanced chemical equation for the reaction of aqueous solutions of lead(II) nitrate and potassium iodide
to produce solid lead (II) iodi de and aqueous potassium nitrate.
Help pleaseee
Answer: Pb(NO3)2(aq) + 2KI(aq) —> PbI2(s) + 2KNO3(aq)
Explanation:
Dale is speaking to a group of students about the importance of extracurricular activities. He provides specific scenarios to show the audience how the information presented will affected them directly. Dale is fulfilling which goal of informational speaking?
to enhance understanding
to be heard
to maintain interest
to be remembered
A desert that contains plants and animals that have been there a long time is
an example of
If I dilute 334.75 mL of 1.28 M lithium acetate solution to a volume of 822.18 ml, what
will the concentration of this solution be?
Answer:
C₂ = 0.52 M
Explanation:
Given data:
Initial volume = 334.75 mL
Initial concentration = 1.28 M
Final volume = 822.18 mL
Final concentration = ?
Solution:
C₁V ₁ = C₂V₂
By putting values,
1.28 M×334.75 mL = C₂×822.18 mL
C₂ = 1.28 M×334.75 mL / 822.18 mL
C₂ = 428.48 M.mL / 822.18 mL
C₂ = 0.52 M
Classify the following compounds as binary ionic, ternary ionic, or molecular.
Answer:bro u already have an answer why are you asking?
Explanation:
Please help me thanks so much!?!?!?
Answer:
Lighting the stove and cooking the meat are both chemical changes.
Explanation:
Both fire and cooking are chemical changes.
Answer:
the second one
Explanation:
Which of the following contains a polyatomic ion?
sodium iodide
carbon monoxide
Iron II oxide
ammonium chloride
Answer:
i think its oxide not too sure
Answer:
Its should be ammonium chloride.
A picture to help you with another question like this
How many cells are a result of Meiosis?
Answer:
2
Explanation:
Cells divide and reproduce in two ways, mitosis and meiosis. Mitosis results in two identical daughter cells, whereas meiosis results in four sex cells.
Define degree of hardness of water? Mention different units.
Answer:
Degree of hardness is defined as the number of parts of calcium carbonate or equivalent to various calcium and magnesium salts present in a million parts of water by mass.
Explanation:
General guidelines for classification of waters are: 0 to 60 mg/L (milligrams per liter) as calcium carbonate is classified as soft; 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard. Lime scale buildup inside a water pipe
Units: mg/l , ppm , kg/[tex]m^{3}[/tex] , ppb , g/L
Given:
BO3 + 3Mg → 3MgO + B
1. How many moles of Mg are required if 2 moles of B are produced?
Answer:
6moles of Mg
Explanation:
The reaction expression is given as:
BO₃ + 3Mg → 3MgO + B
Given:
Number of moles of B produced = 2 moles
Unknown:
Number of moles of Mg required = ?
Solution:
From the balanced reaction expression:
1 mole of B is produced from 3 moles of Mg
2 moles of B will be produced from 2 x 3 = 6moles of Mg
What is the iupac name of the following compound?
2,2-dimethyl-4-ethylheptane
Answer:
The IUPAC name of the compound has already been given which is 2,2-dimethyl-4-ethylheptane.
Explanation:
The IUPAC (International Union of Pure and Applied Chemistry) is an authority in chemistry that provides a guideline and standardized methods in the naming of compounds formed from the periodic table.
In order the give an IUPAC name to a compound, certain steps needs to be followed, these includes:
--> Identify the functional group in the compound as this will form the suffix. For example if the functional group is an alkane the suffix will be -ane.
--> Identify the longest carbon chain (it may not be a straight chain) that contains the functional group. This forms the prefix. Example: if the longest carbon chain is 7 carbon atoms then the prefix will be hept-
--> All the carbons of the longest chain should be numbered
--> Identify branched groups on the chain and name them according to the number of carbon atoms. They usually end with -yl.
--> Finally, combine the elements of the name is a single word.
The structural formula of the IUPAC compound can be found in the attached file for a better understanding. The branched groups are circled.