Answer:
Formulas
3.2 Determining Empirical and Molecular Formulas
Learning Objectives
By the end of this section, you will be able to:
Compute the percent composition of a compound
Determine the empirical formula of a compound
Determine the molecular formula of a compound
The previous section discussed the relationship between the bulk mass of a substance and the number of atoms or molecules it contains (moles). Given the chemical formula of the substance, one may determine the amount of the substance (moles) from its mass, and vice versa. But what if the chemical formula of a substance is unknown? In this section, these same principles will be applied to derive the chemical formulas of unknown substances from experimental mass measurements.
Percent Composition
The elemental makeup of a compound defines its chemical identity, and chemical formulas are the most succinct way of representing this elemental makeup. When a compound’s formula is unknown, measuring the mass of each of its constituent elements is often the first step in the process of determining the formula experimentally. The results of these measurements permit the calculation of the compound’s percent composition, defined as the percentage by mass of each element in the compound. For example, consider a gaseous compound composed solely of carbon and hydrogen. The percent composition of this compound could be represented as follows:
%H=mass Hmass compound×100%
%C=mass Cmass compound×100%
If analysis of a 10.0-g sample of this gas showed it to contain 2.5 g H and 7.5 g C, the percent composition would be calculated to be 25% H and 75% C:
%H=2.5g H10.0g compound×100%=25%
%C=7.5g C10.0g compound×100%=75%
EXAMPLE 3.9
Calculation of Percent Composition
Analysis of a 12.04-g sample of a liquid compound composed of carbon, hydrogen, and nitrogen showed it to contain 7.34 g C, 1.85 g H, and 2.85 g N. What is the percent composition of this compound?
Solution
To calculate percent composition, divide the experimentally derived mass of each element by the overall mass of the compound, and then convert to a percentage:
%C=7.34g C12.04g compound×100%=61.0%%H=1.85g H12.04g compound×100%=15.4%%N=2.85g N12.04g compound×100%=23.7%
The analysis results indicate that the compound is 61.0% C, 15.4% H, and 23.7% N by mass.
Check Your Learning
A 24.81-g sample of a gaseous compound containing only carbon, oxygen, and chlorine is determined to contain 3.01 g C, 4.00 g O, and 17.81 g Cl. What is this compound’s percent composition?
ANSWER:
12.1% C, 16.1% O, 71.8% Cl
Determining Percent Composition from Molecular or Empirical Formulas
Percent composition is also useful for evaluating the relative abundance of a given element in different compounds of known formulas. As one example, consider the common nitrogen-containing fertilizers ammonia (NH3), ammonium nitrate (NH4NO3), and urea (CH4N2O). The element nitrogen is the active ingredient for agricultural purposes, so the mass percentage of nitrogen in the compound is a practical and economic concern for consumers choosing among these fertilizers. For these sorts of applications, the percent composition of a compound is easily derived from its formula mass and the atomic masses of its constituent elements. A molecule of NH3 contains one N atom weighing 14.01 amu and three H atoms weighing a total of (3 × 1.008 amu) = 3.024 amu. The formula mass of ammonia is therefore (14.01 amu + 3.024 amu) = 17.03 amu, and its percent composition is:
%N=14.01amu N17.03amuNH3×100%=82.27%%H=3.024amu H17.03amuNH3×100%=17.76%
This same approach may be taken considering a pair of molecules, a dozen molecules, or a mole of molecules, etc. The latter amount is most convenient and would simply involve the use of molar masses instead of atomic and formula masses, as demonstrated Example 3.10. As long as the molecular or empirical formula of the compound in question is known, the percent composition may be derived from the atomic or molar masses of the
Given 450.98 g of Cu(NO3)2, how many moles of Ag can be made? Provide your final answer rounded to two decimal places.
Cu + 2 AgNO3 → Cu(NO3)2 + 2 Ag
Answer:
4.82 moles of Ag.
Explanation:
We'll begin by calculating the number of mole in 450.98 g of Cu(NO₃)₂. This can be obtained as follow:
Molar mass of Cu(NO₃)₂ = 63.5 + 2[14 + (16×3)]
= 63.5 + 2[14 + 48]
= 63.5 + 2[62]
= 63.5 + 124
= 187.5 g/mol
Mass of Cu(NO₃)₂ = 450.98 g
Mole of Cu(NO₃)₂ =?
Mole = mass /Molar mass
Mole of Cu(NO₃)₂ = 450.98 / 187.5
Mole of Cu(NO₃)₂ = 2.41 moles
Next, we shall determine the number of mole of Cu needed to produce 450.98 g (i.e 2.41 moles) of Cu(NO₃)₂. This can be obtained as follow:
Cu + 2AgNO₃ —> Cu(NO₃)₂ + 2Ag
From the balanced equation above,
1 mole of Cu reacted to produce 1 mole of Cu(NO₃)₂.
Therefore, 2.41 moles of Cu will also react to produce 2.41 moles of Cu(NO₃)₂.
Thus, 2.41 moles of Cu is needed for the reaction.
Finally, we shall determine the number of mole of Ag produced from the reaction. This can be obtained as follow:
From the balanced equation above,
1 mole of Cu reacted to produce 2 moles of Ag.
Therefore, 2.41 moles of Cu will react to produce = 2× 2.41 = 4.82 moles of Ag.
Thus, 4.82 moles of Ag were obtained from the reaction.
What is the percent composition of Mg in the compound Mg3(PO4)2?
A 21.92%
B 23.57%
C 32.32%
D 27.74%
Answer:
D 27.74%
Explanation:
Percent composition of Magnesium (Mg) in Magnesium Phosphate compound ie Mg3(PO4)2 = 27.74%
Answer:
The answer is D
Explanation:
I took the test
can someone help me?
Answer:
no, and next time take it right
Explanation:
A chemistry student needs 50.0ml of tetrahydrofuran for an experiment. By consulting the CRC Handbook of Chemistry and Physics, the student discovers that the density of tetrahydrofuran is . Calculate the mass of tetrahydrofuran the student should weigh out. Be sure your answer has the correct number of significant digits.
Answer:
44.45 g of tetrahydrofuran.
Explanation:
From the question given above, the following data were obtained:
Volume of tetrahydrofuran = 50 mL
Density of tetrahydrofuran = 0.889 g/mL
Mass of tetrahydrofuran =?
Density of a substance is simply defined as the mass of the substance per unit volume of the substance. Mathematically, density is expressed as shown below:
Density = mass / volume
With the above formula, we shall determine the mass of tetrahydrofuran needed. This can be obtained as follow:
Volume of tetrahydrofuran = 50 mL
Density of tetrahydrofuran = 0.889 g/mL
Mass of tetrahydrofuran =?
Density = mass / volume
0.889 = mass / 50
Cross multiply
Mass = 0.889 × 50
Mass of tetrahydrofuran = 44.45 g
Therefore, the student should weigh out 44.45 g of tetrahydrofuran.
Calculate the kinetic energy of an electron ejected from a piece of sodium (Φ = 4.41x10–19 J) that is illuminated with 265 nm light.
in Joules
Answer:
Explanation:
Energy of falling radiation having wavelength of 265 nm
= h c / λ where h is plank's constant , c is velocity of light and λ is wavelength of radiation . Putting the values
Energy of light photon = 6.6 x 10⁻³⁴ x 3 x 10⁸ / 265 x 10⁻⁹
= .0747 x 10⁻¹⁷
= 7.47 x 10⁻¹⁹ J .
Work function of sodium is 4.41 x 10⁻¹⁹
So kinetic energy of ejected electron = energy of falling photon - work function
= 7.47 x 10⁻¹⁹ - 4.41 x 10⁻¹⁹
= 3.06 x 10⁻¹⁹ eV .
There are four conditions an atom needs to meet to participate in hydrogen bonding. It needs to be_______ enough not to bump into other atoms when approaching the 1s orbital of the hydrogen, it needs to carry at least one________ atom, it needs to be_________enough to create a delta on the connected hydrogen, and it needs to have at least one________.
Answer:
The conditions are
1) Small enough
2) Electronegative atom
3) highly electronegative
4) lone pair of electrons
The correct statement therefore is
It needs to be small enough not to bump into other atoms when approaching the 1s orbital of the hydrogen, it needs to carry at least one electronegative atom, it needs to be highly electronegative enough to create a delta on the connected hydrogen, and it needs to have at least one lone pair of electrons.
Explanation:
Hydrogen bonding is a type of intermolecular bond that occurs between the partial positive charge (delta) on a hydrogen atom bonded to a small highly electronegative element (like nitrogen, oxygen or fluorine) and the free electrons on another electronegative element of another molecule.
The hydrogen atom with the partial positive charge (delta) is known as the hydrogen bond donor, while the electronegative element, carrying lone electrons is called the hydrogen bond acceptor.
Let's take a deeper look at these terms:
1) Hydrogen bond donor
Using water (H₂O) as an example, the high electronegativity of the oxygen atom covalently bonded to the hydrogen atom draws the lone electron in the 1s orbital of the hydrogen atom, creating a partial positive charge (d⁺) on the hydrogen atom. This is what happens within one water molecule
2) Hydrogen bond acceptor
When two or more molecules of water interact, the partial positive charge (d⁺) on the hydrogen atom of one molecule, is attracted to the valence or free electrons on the oxygen atom of a nearby molecule of water thus creating a dipole-dipole intermolecular bond known as a hydrogen bond.
For the hydrogen bond to be effective, the electronegative atom bonded to the hydrogen acting as the hydrogen bond donor in the first water molecule needs to be small enough so as not to disrupt the 1s orbital of the hydrogen atom. The smaller the size of the electronegative atom, the stronger the partial negative charge created on the hydrogen atom.
The valence or free pair of electrons on the electronegative (oxygen) atom of the second molecule of water (hydrogen bond acceptor) is what attracts the partial positive charge on the hydrogen atom to create the hydrogen bond
Two colorless chemicals combine inside a glow
stick. When the chemicals combine, they produce
brightly colored light. The glow stick's temperature
does not change.
emission of heat
emission of light
color change
formation of gas
Answer:
Option B & Option C
Explanation:
correct on edge! :D
When chemicals combine chemical change takes place which is accompanied by emission of heat and light.
What is a chemical change?Chemical changes are defined as changes which occur when a substance combines with another substance to form a new substance.Alternatively, when a substance breaks down or decomposes to give new substances it is also considered to be a chemical change.
There are several characteristics of chemical changes like change in color, change in state , change in odor and change in composition . During chemical change there is also formation of precipitate an insoluble mass of substance or even evolution of gases.
There are three types of chemical changes:
1) inorganic changes
2)organic changes
3) biochemical changes
During chemical changes atoms are rearranged and changes are accompanied by an energy change as new substances are formed.
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please help. im freaking out rn. i have like 40 missing assignments please
Answer:
I'm pretty sure its the one that says very little at the beginning but if I get it wrong I'm sorry
Heat will continue to move until the objects or areas have reached the same ______.
Answer: Thermal Equilibrium
Explanation:
Answer:
temperature
Explanation:
I think that's it i'm sorry if i'm wrong
18. What is one of the three things that cause the surface currents of the oceans?
A.differences in salinity
B.temperature differences
C. density differences
D. Coriolis effect
Answer:
b. temperature difference
If 3.53 g of CuNO, is dissolved in water to make a 0.330 M solution, what is the volume of the solution in milliliters?
Answer:
84.8 mL
Explanation:
From the question given above, the following data were obtained:
Mass of CuNO₃ = 3.53 g
Molarity of CuNO₃ = 0.330 M
Volume of solution =?
Next, we shall determine the number of mole in 3.53 g of CuNO₃. This can be obtained as follow:
Mass of CuNO₃ = 3.53 g
Molar mass of CuNO₃ = 63.5 + 14 + (16×3)
= 63.5 + 14 + 48
= 125.5 g/mol
Mole of CuNO₃ =?
Mole = mass / Molar mass
Mole of CuNO₃ = 3.53 / 125.5
Mole of CuNO₃ = 0.028 moles
Next, we shall determine the volume of the solution. This can be obtained as follow:
Molarity of CuNO₃ = 0.330 M
Mole of CuNO₃ = 0.028 moles
Volume of solution =?
Molarity = mole /Volume
0.330 = 0.028 / Volume
Cross multiply
0.330 × Volume = 0.028
Divide both side by 0.330
Volume = 0.028 / 0.330
Volume = 0.0848 L
Finally, we shall convert 0.0848 L to millilitres (mL). This can be obtained as follow:
1 L = 1000 mL
Therefore,
0.0848 L = 0.0848 L × 1000 mL / 1 L
0.0848 L = 84.8 mL
Therefore, the volume of the solution is 84.8 mL.
What is the molecular formula of the molecule that has an empirical formula of C2H40 and a molar mass of 176.21 g/mol?
Type your answer using the following format:
CuCl2 for CuCl2.
Answer:
C8H16O4
Explanation:
C2H4O= 24+4+16
44
n=molar mass/empirical formula
n=176.21/44
=4
Therefore
Molar Formula= (C2H4O)4=C8H16O4
Which has more calories: table sugar or aspartame?
Hello there!
Aspartame has 4 kilocalories of energy per gram and table sugar has 3.9 kilocalories. They are pretty much same but aspartame is 200 times sweeter than sucrose so probably would be aspartame that has more calories.
Vitamin C is a covalent compound with the molecular
formula C6H8O6. The recommended daily dietary
allowance of vitamin C for children aged 4-8 years is
0.000142mol. What is the mass of this allowance in grams?
The mass allowance of Vitamin C for children aged 4-8 years is equal to 0.025 grams.
What is a mole?A mole can be defined as a standard unit that can be utilized to evaluate the number of entities such as atoms, molecules, ions, or other particular particles in a particular amount of the substance.
The number of elementary entities present in one mole of any chemical substance was found to be equal to 6.023 × 10²³ which is also known as the Avogadro number.
Given, the number of moles of vitamin C = 0.000142 moles
Given, the molecular formula of Vitamin C is C₆H₈O₆.
The mass of one mole of C₆H₈O₆ = 176 g
One mole of Vitamin C has mass = 176 g
0.000142 mol of Vitamin C has mass = 0.000142×176 = 0.025 g
Therefore, the mass of 0.000142 mol of Vitamin C is 0.025 g.
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Name each of the following organic molecules. 
How many grams of sulfur must be burned to give 100.0 g of So2
Answer:
50 g of S are needed
Explanation:
To star this, we begin from the reaction:
S(s) + O₂ (g) → SO₂ (g)
If we burn 1 mol of sulfur with 1 mol of oxygen, we can produce 1 mol of sulfur dioxide. In conclussion, ratio is 1:1.
According to stoichiometry, we can determine the moles of sulfur dioxide produced.
100 g. 1mol / 64.06g = 1.56 moles
This 1.56 moles were orginated by the same amount of S, according to stoichiometry.
Let's convert the moles to mass
1.56 mol . 32.06g / mol = 50 g
Please answer, this is due in 30 minutes
Answer:
0.591 g of magnesium phosphate is the theoretical yield.
Magnesium nitrate is the limiting reactant.
Explanation:
Hello!
In this case, since the balanced reaction turns out:
[tex]3Mg(NO_3)_2+2Na_3PO_4\rightarrow Mg_3(PO_4)_2+6NaNO_3[/tex]
Next, we compute the grams of magnesium phosphate yielded by each reactant, considering the present mole ratios and molar masses:
[tex]m_{Mg_3(PO_4)_2}^{by\ Mg(NO_3)_2}=1.00gMg(NO_3)_2*\frac{1molMg(NO_3)_2}{148.31gMg(NO_3)_2}*\frac{1molMg_3(PO_4)_2}{3molMg(NO_3)_2} *\frac{262.86gMg_3(PO_4)_2}{1molMg_3(PO_4)_2} \\\\m_{Mg_3(PO_4)_2}^{by\ Mg(NO_3)_2}= 0.591gMg_3(PO_4)_2\\\\m_{Mg_3(PO_4)_2}^{by\ Na_3PO_4}=1.00gNa_3PO_4*\frac{1molNa_3PO_4}{163.94gNa_3PO_4}*\frac{1molMg_3(PO_4)_2}{2molNa_3PO_4} *\frac{262.86gMg_3(PO_4)_2}{1molMg_3(PO_4)_2} \\\\m_{Mg_3(PO_4)_2}^{by\ Na_3PO_4} = 0.802gMg_3(PO_4)_2[/tex]
Thus, we infer that the correct theoretical yielded mass is 0.591 g as magnesium nitrate is the limiting reactant for which it produces the fewest grams of product.
However, is not possible to compute the percent yield since no actual yield is given, and must be provided or indicated by the problem or an experiment and it not here, nevertheless, you may compute the percent yield by dividing the actual yield by the theoretical and then multiplying by 100:
[tex]Y=\frac{actual}{0.591g}*100\%[/tex]
Best regards!
please help me with this problem
the amount of reactants = the amount of products
N2 + 3H2 --> 2NH3
Consider the following reaction where K. = 9.52 10 2 at 350 K.
CH,(g) + CC14(2)—2CH2Cl2(g)
A reaction mixture was found to contain 2.21*10-2 moles of CH4(E), 3.8710-2 moles of CC1,(g) and 1.06-10-2 moles of CH,C12(2), in
a 1.00 liter container
Is the reaction at equilibrium?
If not, what direction must it run in order to reach equilibrium?
The reaction quotient, Qc equals
The reaction
A. must run in the forward direction to reach equilibrium
B. must run in the reverse direction to reach equilibrium
C. is at equilibrium
Answer:
The correct answer is A :))
What is the energy of an electron in the third energy level of hydrogen?
Answer:
Electrons in a hydrogen atom must be in one of the allowed energy levels. If an electron is in the first energy level, it must have exactly -13.6 eV of energy.
...
Energy Levels of Electrons.
Energy Level Energy
1 -13.6 eV
2 -3.4 eV
3 -1.51 eV
4 -.85 eV
I need help with this!!!
Answer:
0.73g/cm^3
Explanation:
d=m/v
d=11/15
d=0.73
Write the equilibrium expression of each chemical equation.
2H2S(g) 2H2(g) + S2(g)
Answer:
[H2]2[S2][H2S]2Kc=[H2]2[S2][H2S]2
Explanation:
2H2S(g)⇋2H2(g)+S2(g)2H2S(g)⇋2H2(g)+S2(g)
The equilibrium constant expression in terms of concentrations is:
Kc=[H2]2[S2][H2S]2Kc=[H2]2[S2][H2S]2.
The equilibrium expression for the given reaction can be written in terms of equilibrium constant which is the ratio of power of molar concentration of the product to the product of power of molar concentration of the reactants.
What is equilibrium?Equilibrium is a state for a reversible reaction where, the rate of forward reaction is equal to the rate of backward reaction. The rate of a reaction is the rate of decrease in the concentration of reactants or the rate of increase in the concentration of the products.
The given reaction at equilibrium state is written as:
[tex]\rm 2H_{2}S (g)\leftrightharpoons 2H_{2} (g)+ S_{2}(g)[/tex]
The equilibrium constant Kb is ratio of power of molar concentration of the product to the product of power of molar concentration of the reactants.
[tex]Kb = \rm \frac{[H_{2}S]^{2}}{[H_{2}]^{2} [S_{2}]}[/tex]
The rate of the reaction will be r = Kb [H₂]² [S₂].
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If two reactant molecules collide with each other what two reasons might they not combine ?
Why is it important to know gas properties at STP?
Answer:
STP values are most often cited for gases because their characteristics change dramatically with temperature and pressure. One common definition of STP is a temperature of 273 K (0° Celsius or 32° Fahrenheit) and the standard pressure of 1 atm. Under these conditions, one mole of a gas occupies 22.4 L.
Consider the following chemical equilibrium:
N2 (g) + 3H2 ⇌ 2NH3
Now write an equation below that shows how to calculate Kp from Kc for this reaction at an absolute temperature .
Answer:
Kp = Kc (RT) ^(-2)
Explanation:
For the reaction;
N2 (g) + 3H2 ⇄ 2NH3(g)
We can write;
Kc = [NH3]^2/[N2] [H2]^3
But
Kp = pNH3^2/pN2 . PH2^3
To convert from Kc to Kp
Kp = Kc (RT) ^Δn
where Δn is the change in number of moles going from reactants
to products.
For this reaction;
Δn = 2- (3+1) = -2
Kp = Kc (RT) ^(-2)
A beaker in your laboratory drawer has an inside diameter of 6.8 cm and a height of 8.9 cm. Using the equation V= arh, calculate the volume of the beaker, expressed in milliliters.
Answer:
323.22 ml
Explanation:
Given that :
Diameter, d = 6.8cm
Height, h = 8.9cm
V = arh
Recall :
Volume, V = πr²h
Radius, r = diameter / 2 = 6.8 / 2 = 3.4cm
V = π * 3.4^2 * 8.9
V = 323.21961 cm³
Recall:
1ml = 1cm³
Hence,
323.21961 cm³ = 323.21961 ml
Volume = 323.22 ml
Iron is a metal. The structure of iron is described as a lattice of positive ions in a sea of
electrons. Which of the following statements about iron are correct?
1 iron conducts electricity because the electrons are free to move
2 iron has a high melting point due to the strong covalent bonds
3 iron is an alloy
4 iron is malleable because the layers of atoms can slide over one another
A. 1 only
B. 1 and 3
C. 1 and 4
D. 2, 3 and 4
Answer: 1and 4
Explanation: iron is an element not an alloy. An ionic lattice is not bonded covalently.
Please explain to me!!!
Answer:
nice handwrtting
Explanation:
Which of the following metals (M) will form an ionic compound with nitrogen with the general formula M3N2?
Answer:
There are no options provided dude,
But i guess the answer will be a metal with valency 2 for sure as the subscript given for N in 'M3N2' is 2 so the valency of the metal u need to select will be 2 for sure
It can be magnesium or some other if the provided options in real question has Mg then its the answer
A molten sample of 1.00kg of iron with a specific heat of 0.385J/g.K at 1000.K is immersed in a sample of water. If the water absorbs 270 kJ of heat what is the final temperature of the iron?
I need all the process.
Answer:
298. 7 K.
Explanation:
Hello!
In this case, since equation we use to compute the heat in a cooling or heating process is:
[tex]Q=mC(T_f-T_i)[/tex]
Whereas we are given the heat, mass, specific heat and initial temperature. Thus, we infer that we need to solve for the final temperature just as shown below:
[tex]T_f=T_i+\frac{Q}{mC}\\\\T_f=1000 K+\frac{-270000J}{1000g*0.385\frac{J}{g*K} } \\\\T_f=298.7 K[/tex]
It is important to notice that the iron release heat as water absorbs it, that is why it is taken negative.
Best regards!