Draw the Lewis dot diagram for lithium (p.180)

The average atomic mass of the given isotopes of Halfnium is 178.55 amu

The average atomic mass of an element is equal to the sum of its isotope masses multiplied by it's own natural abundance (the decimal associated with the percent of atoms of that element for a given isotope).

In order to determine the weighted average, we must consider the % natural abundances of each isotope. The atomic mass of an element is the weighted average of the atomic masses of the element's naturally occurring isotopes. Determine the average atomic mass by using atomic masses and percentage abundances of each isotope. To convert each percentage abundance to decimal form, divide it by 100. Multiply this figure by the atomic mass of the isotope. To get the average atomic mass, add the atomic masses of each isotope together.

To determine the average atomic mass of Halfnium, the mass fractions of the isotopes multiplied by their respected atomic masses must all be added.

Using 100 atoms as the basis, calculate the mass fractions (m1, m2,...m5):

m1 =   5/100 = 0.05

m2 = 19/100 = 0.19

m3 = 27/100 = 0.27

m4 = 14/100 = 0.14

m5 = 35/100 = 0.35

Multiplying the mass fractions with the atomic masses of the respective isotopes.

Average atomic mass of Halfnium is:

Avg = (m1 x 176) + (m2 x 177) + (m3 x 178) + (m4 x 179) + (m5 x 180)

Avg = (0.05 x 176) + (0.19 x 177) + (0.27 x 178) + (0.14 x 179) + (0.35 x 180)

Avg = 178.55 amu

Therefore, the average atomic mass of Halfnium based on the data for its given isotopes is 178.55 amu.

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Answer:

mercury

Explanation:

mercury is a metal on the periodic table which is liquid at room temperature

Answer: Hormones are are the body's chemical messengers, sending signals into the bloodstream and tissues. Hormones work slowly, over time, and affect many different processes, including growth and development, metabolism – how your body gets energy from the foods you eat- sexual function, reproduction, and mood

Difference between crystallization and evaporation to dryness : crystallization is the formation of solid crystal from liquid whereas evaporation is the formation of vapor from liquid.

Crystallization is defined as the the process in which pure solid separates in the form of crystal from solution .

Evaporation to dryness is  used to separate solute thermally when soluble solid does not decompose on heating. crystallization is better than evaporation to dryness because in the process of evaporation some solid in the mixture get decomposed leaving impurities. during the process of evaporation.

The major difference is that in crystallization is the formation of solid crystal from liquid whereas evaporation is the formation of vapor from liquid.

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1. False, 2. True, 3. True, 4. False, 5. True, 6. False, 7. True, 8. False, 9.  Incomplete and 10. True.

1. Atoms have no weight - False

Atomic mass is the total mass of an atom. This is roughly equal to the total number of protons and neutrons with a small addition of electrons.

2. The electron is the heaviest part of the atom - in fact

3. All protons have the same mass - True

4. All atoms have the same mass - False

The mass of each element depends on the number of protons and neutrons it contains.

5. All neutrons have the same mass. - True

6. An oxygen atom weighs as much as a nitrogen atom. - False

o2 has a molecular weight of 15.9994 g/mol, and the molar mass of nitrogen is 14.0067 g/mol.

7. All oxygen atoms have the same mass - True

8. If we add neutrons and electrons to find the mass of an atom, the atomic mass of calcium is 40.08 - False

The number of protons and neutrons in an element determines its mass number. Protons and neutrons are the mass numbers.

9. The circular mass is 41, which is not quite correct.

10. Isotopes are identical atoms with differing numbers of protons. - True

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Get the fire blanket and notify the teacher.

If your clothing catches fire do not run or do anything else to fan the flames. Immediately drop it on the ground and roll it to extinguish the flames. The laboratory is also equipped with fire blankets to extinguish clothing fires. Used by instructors as needed to completely extinguish flames.

Long hair should be tied up and long sleeves should not be worn. Always keep hair clothing, and hands at a safe distance from flames. Never touch the open flame with your hands. Use tongs when holding objects in flames. Long hair can fall on lab benches or come into contact with chemical or biological agents.

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Answer:

1st option

Explanation:

At sea level, atmospheric pressure is high, and water boils at 100 °C (212 °F)

Answer:

the third one ;)

Explanation:

The molarity of a solution is 3.743M.

Molarity of a solution:

Molar concentration is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of the amount of substance per unit volume of solution.

The formula for the molarity of a solution:

M = [tex]w_{B}[/tex] × 1000 / [tex]M_{B}[/tex] × V(ml)

[tex]w_{B}[/tex] = 50.54g

[tex]M_{B}[/tex] = molecular mass of water(H2O) = 2 + 16 = 18

V = Volume = 750ml

Putting the value in the equation, we get

M = 50.54 ×1000 / 18 × 750

   = 50540 / 13500

    = 3.743M

Therefore the molarity of a solution is 3.743M

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The molecular formula is [tex]\rm C_2O_8[/tex]. The empirical formula is [tex]\rm C_2H_1_2O_6[/tex] which is the simplest from.

Molecular formula is defined as  a chemical formula that gives the total number of atoms of each element in each molecule of a substance.

It can also be defined as a formula derived from molecules that indicates the total number of individual atoms in the molecule of a compound.

Empirical formula is defined as a chemical formula that depicts the simplest elemental ratio of a compound rather than the total number of atoms in the molecule.

Molecular formula = n - empirical formula

Thus, the molecular formula is [tex]\rm C_2O_8[/tex]. The empirical formula is [tex]\rm C_2H_1_2O_6[/tex] which is the simplest from.

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The intrinsic carrier concentration and the fraction of ionized atoms of silicon at -55℃, 0℃, 20℃, 75℃, 125℃ is calculated below.

The intrinsic carrier concentration in intrinsic material is the number of electrons found in the conduction band or holes in the valence band. This quantity of carriers is determined by the material's band gap as well as its temperature.

Because the number of holes equals the number of electrons, the concentration of each is equal to some amount, ni, and this quantity is known as the intrinsic carrier concentration, and the pure semiconductor material is referred to as intrinsic material.

Given:

B = 5.4 x [tex]10^{31}[/tex]

[tex]E_G[/tex] = 1.12 ev for silicon

K = 8.62 x [tex]10^{-5}[/tex]

Silicon crystal = 5 x [tex]10^{22}[/tex] atoms/[tex]cm^3[/tex]

To find:

Intrinsic carrier concentration, ni = ?

Fraction of ionized atom = ?

Formula:

[tex]ni^2 = BT^3 e^{\frac{-E_G}{KT}[/tex]

Fraction of ionized atom = ni / 5 x [tex]10^{22}[/tex]

Calculations:

(a) For -55℃:

T = -55 + 273 = 218K

ni = [tex]5.4 * 10^{31} * 218^3 * e^{(\frac{-1.12}{8.62 * 10^{-5} * 218})}[/tex]

ni = 2.7018 x [tex]10^6[/tex] carriers/[tex]cm^3[/tex]

Fraction of ionized atom = 2.7018 x [tex]10^6[/tex] / 5 x [tex]10^{22}[/tex]

Fraction of ionized atom = 5.403 x [tex]10^{-17}[/tex] atoms/[tex]cm^3[/tex]

(b) For 0℃:

T = 0 + 273 = 273K

ni = [tex]5.4 * 10^{31} * 273^3 * e^{(\frac{-1.12}{8.62 * 10^{-5} * 273})}[/tex]

ni = 1.53 x [tex]10^9[/tex] carriers/[tex]cm^3[/tex]

Fraction of ionized atom = 1.53 x [tex]10^9[/tex] / 5 x [tex]10^{22}[/tex]

Fraction of ionized atom = 3.07 x [tex]10^{-14}[/tex] atoms/[tex]cm^3[/tex]

(c) For 20℃:

T = 20 + 273 = 293K

ni = [tex]5.4 * 10^{31} * 293^3 * e^{(\frac{-1.12}{8.62 * 10^{-5} * 293})}[/tex]

ni = 8.65 x [tex]10^9[/tex] carriers/[tex]cm^3[/tex]

Fraction of ionized atom = 8.65 x [tex]10^9[/tex] / 5 x [tex]10^{22}[/tex]

Fraction of ionized atom = 1.73 x [tex]10^{-13}[/tex] atoms/[tex]cm^3[/tex]

(d) For 75℃:

T = 75 + 273 = 348K

ni = [tex]5.4 * 10^{31} * 348^3 * e^{(\frac{-1.12}{8.62 * 10^{-5} * 348})}[/tex]

ni = 3.724 x [tex]10^{11}[/tex] carriers/[tex]cm^3[/tex]

Fraction of ionized atom = 3.724 x [tex]10^{11}[/tex] / 5 x [tex]10^{22}[/tex]

Fraction of ionized atom = 7.449 x [tex]10^{-12}[/tex] atoms/[tex]cm^3[/tex]

(e) For 125℃:

T = 125 + 273 = 398K

ni = [tex]5.4 * 10^{31} * 398^3 * e^{(\frac{-1.12}{8.62 * 10^{-5} * 398})}[/tex]

ni = 4.75 x [tex]10^{12}[/tex] carriers/[tex]cm^3[/tex]

Fraction of ionized atom = 4.75 x [tex]10^{12}[/tex] / 5 x [tex]10^{22}[/tex]

Fraction of ionized atom = 9.51 x [tex]10^{-11}[/tex] atoms/[tex]cm^3[/tex]

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We can't you use the equation Q = mc∆T to calculate how much thermal energy is needed to melt or boil a substance because this equation is to calculate for heat energy transferred between two objects where m is the mass of each object and c is the specific heat capacity

Thermal energy refers to the energy contained within a system that is responsible for its temperature and for thermal energy for melt any substance is latent heat and during boiling of any substances the heat energy supplied is used in increasing the energy of the water molecule which changes its state from liquid to gaseous

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The independent variable as we can see from the experiment that have been described in this case is the brand of fertilizer that was used in the study.

When we talk about an experiment, we are talking about the way by which the relation ship between the dependent and the independent variable could be studied. In the experiment, there is a dependent variable which would change values when the variable that is under study in the particular experiment changes value. We have to know that in the realm if science, it is only by the means of experiments that we can be able to establish cause and effect relationships.

In this case, we can see that the experiment that the students were working on has to do with trying to actually find out if  brand X fertilizer will affect the growth of Lily plants. This means that they were studying the effect of a fertilizer brand on the growth of the crops.

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19.2g/cm³

D = m / V

24.20g / 1.92ml = 19.2g/cm³

16:32=1:2 hence the Law of Multiple Proportion holds true

According to the Law of Multiple Proportion, the mass of one element that is combined with a fixed mass of the second element will always be ratios of whole numbers when two components combine to generate more than one compound.

For illustration, suppose there are two molecules of CO (carbon monoxide) and CO 2. (carbon dioxide).

CO is equal to 12g of carbon and 16g of oxygen.

CO2 is made up of 12 grams of carbon and 32 grams of oxygen.

The two compounds are 16:32=1:2 in terms of the mass of oxygen.

This establishes the law of multiple proportions.

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Yes, there are chemical reactions that are brought about through the use of light (such as free radical halogenation) and there are chemical reactions that produce light (chemiluminescence).

Numerous reactions use light as an initiator. For example, in various examples of free radical halogenation (a reaction between a hydrocarbon and a halogen molecule, where alkyl halides are formed), light is needed to break the bond between the bromine atoms in order to form bromine radicals that then initiate the chain reaction leading to the formation of the product.

The phenomenon of producing light through a chemical reaction is called chemiluminescence. It is relatively rare, but not unheard of. One example is the reaction between luminol and hydrogen peroxide, which forms 3-aminophthalate and releases light.

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Answer:

different number of neutrons

The atomic mass of every element may be simply calculated using the number of protons and neutrons in the nucleus.

The atomic mass can be approximated by summing the number of protons and neutrons in the atom. The average mass of an element's atoms that are meaningfully measured in the atomic mass unit (amu) is defined as its atomic mass. It should be noted that the atomic mass is calculated by adding the masses of all the element's isotopes. This is the most precise method for calculating the relative atomic mass.

However, if we do not wish to compute the precise atomic mass of one of the elements, we may simply sum the number of protons and neutrons in the atom. This provides us a ballpark estimation of the atom's mass. Another way for estimating the atomic mass of any element is to simply double the value of the atomic number that is known for each individual element.

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Answer:get a ruler and find out

Explanation:

measure from tip to tip and post a picture to see

Answer:baby carrots

Explanation:

measure with baby carr

The group with a better result is group 1

Three ways that the groups could improve their results in terms of the crystallization experiment and the melting point investigation are: recrystallisation, elimination of impurity, and heating the solvent.

Group 1's result is better, it is so because they have got the melting point range in a close proximity, that means they do not have a broad range. Smaller the range of melting point, more accurate the compound is synthesized.

3 ways that the groups could improve their results:

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A hiker climbs to the top of a mountain at rate of 0.5 m/hr. The speed of hiker is 1.3 x 10⁻⁴ m/s and the velocity of the hiker is 1.3 x 10⁻⁴ m/s west.

Speed is a scalar quantity. It is used to measure the distance traveled in a period of time. It is represented by -

s = d/Δt

where,

s = speed

d = distance

Δt = change in time

Velocity is a vector quantity. It is used to measure the change in position, that is, displacement over the change in time. It is represented by -

v = Δs / Δt

where,

v = velocity

Δs = change in position/displacement

Δt = change in time

The standard unit of velocity and speed both is m/s.

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In a polypeptide chain, to generate an amide, the peptide bond connects the carboxyl group of one amino acid (x) to the amino group of the subsequent amino acid (y).

A polypeptide chain is defined as a series of amino acids linked together by peptide bonds. Poly stands for numerous, while peptide stands for protein. A polypeptide chain is therefore a chain of protein or amino acid building components. Polypeptide chains are crucial because they are the building blocks of proteins.

The carboxyl group of the first amino acid, w binds with the amino group of the next amino acid, x. The carboxyl group of x binds with the amino group of the y amino acid. Thus, peptide bonds are formed between the w-x-y amino acids making them a polypeptide chain.

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It takes 5.89 x 10¹⁰ Oreos to reach the moon.

The average distance from the Earth to the moon is 385 000.6 km.

Metres = 385 000.6 km × (1000 m/1 km ) = 385 000 600 m

Centimetres = 38 500 060 000 m × (100 cm/1 m) = 38 500 060 000 cm

Oreos = 38 500 060 000 cm × (1 Oreo/0.654 cm) = 58 900 000 000 Oreos

= 5.89 x 10¹⁰ Oreos

Its diameter is around one-quarter that of the Earth (comparable to the width of Australia). The Moon is the Solar System's fifth-largest satellite. It is the largest (and most massive) satellite relative to its home planet and is larger than any other known dwarf planet. [f] According to geophysical criteria, the Moon is a planetary-mass object that became a differentiated rocky body, making it a satellite planet. There is no atmosphere, hydrosphere, or magnetic field. Its surface gravity is around one-sixth that of Earth (0.1654 g). Io, Jupiter's moon, has the highest surface gravity and density of any satellite in the Solar System.

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All of the nitrogen in the N2H4 molecule hybridizes to Sp3.

The combining of two atomic orbitals to create a whole new class of hybridized orbitals is the notion of hybridization in chemistry. Hybrid orbitals with completely distinct energies are often the outcome of this mixing. In hybridization, the same-energy level atomic orbitals are crucial. However, as long as they have an equivalent amount of energy, both fully and partially filled orbitals can participate in this process.

All of the nitrogen in the N2H4 molecule hybridizes to Sp3. N2H4 has a dipole moment of 1.85 D and is polar in nature. The nitrogen atoms in N2H4 have no formal charge. The N2H4 molecule has a trigonal molecular geometry (shape).

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Light energy is used in photosynthesis to convert carbon dioxide and water into glucose and oxygen. 1 glucose molecule and 6 oxygen molecules are produced for every 6 carbon dioxide and 6 water molecules.

C₆H₁₂O₆ is the chemical formula for glucose, a simple sugar. When a glucose molecule is assembled during photosynthesis, it absorbs 12 hydrogen ions from the chloroplast stroma. Reactants in photosynthesis include oxygen, carbon dioxide, ATP, and NADPH. Water and GA3P are both products. Chlorophyll, water, and carbon dioxide are reactants in photosynthesis. When the process is finished, photosynthesis produces oxygen and carbohydrate molecules, most commonly glucose. These sugar molecules contain the energy required by living things to survive.

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In this question, we need to find the value of pressure of a 15 grams sample of CO2 gas, and in order to find this value, we will be using the Ideal gas law formula, which is the following:

PV = nRT

Where:

P = pressure in atm

V = volume in liters, 20 Liters

n = number of moles

R = gas constant, 0.082

T = temperature in kelvin, 0°C = 273 K

The number of moles we need to find based on the mass in the question and based on the molar mass of CO2, 44g/mol:

44g = 1 mol

15g = x moles

44x = 15

x = 15/44

x = 0.34 moles of CO2 in 15 grams

Now we have the values to add to the formula:

P * 20 = 0.34 * 0.082 * 273

20P = 7.61

P = 7.61/20

P = 0.38 atm of pressure

The pressure will be 0.38 atm

The number of milliliters of 3.0m NaOH required to react with 0.5g of Cu2+ to form Cu(OH)2 is 5.249 ml

The reaction is as follows;

2NaOH  + Cu2+  ------------> Cu(OH)2  +  2Na+

From the balanced chemical reaction, 0.5 g of Cu2+ = 0.5/63.5 = 7.874x10-3 moles  (molar mass of Cu2+ = 63.5 g)

Thus, moles of NaOH required = 2*moles of Cu2+ = 0.01575

Now, moles of NaOH = molarityxvolume in litres

or,  3*volume in litres = 0.01575

or, volume in litres  = 5.249*10-3 litres = 5.249 ml

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Calculation of percent yield requires the theoretical yield to be calculated first. Using that method, the percent yield of the reaction is 44%.

To calculate the percent yield of calcium nitride, we first need to calculate the theoretical yield. To do this, we need the molar mass of both calcium (40 g/mol) and calcium nitride (3 * 40 + 2 * 14) g/mol = 148 g/mol.

3 moles of calcium produce 1 mol of calcium nitride so the proportion we can make will look like this:

120 g of calcium : 148 g of calcium nitride = 56.6 g of calcium : X

X = 148 g of calcium nitride * 56.6 g of calcium / 120 g of calcium

X = 69.8 g of calcium nitride

This is the theoretical yield. Calculating the percent yield works like this - we divide the actual mass by the theoretical yield and then multiply that number (that is always supposed to be between 0 and 1) by 100%:

%yield = 100% * 31.0 g / 69.8 g = 44%

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The enthalpy of precipitation of calcium fluoride is -13.974 kJ/mol.

In order to solve this, first we need to write the balanced chemical reaction equation of the reaction in question:

CaCl₂(aq) + 2KF(aq) → CaF₂(s) + 2KCl(aq)

In order to calculate the enthalpy of precipitation (ΔH), we need the amount  of heat released (Q) and the number of moles of CaF₂ (n):

ΔH = Q/n

To calculate the number of moles, we can use the molarity (c = 1.00 M) of the calcium chloride solution and its volume (V = 25 mL = 0.025 L):

c = n/V ⇒ n = c*V

n = 1.00 M * 0.025 L = 0.025 mol

We calculate the amount of heat released (Q) using the following equation:

Q = (t₁ - t₂) * C * m

t₁ - initial temperature (25.0 ⁰C)

t₂ - final temperature (26.7 ⁰C)

C - specific heat capacity (4.184 J/⁰Cg)

m - the mass of the solution

We need the mass of the solution, which we can calculate using the density (d = 1.00 g/mL) and the volume (V = 25 mL + 25 mL = 50 mL) of the solution:

d = m/V ⇒ m = d*V

m = 1.00 g/mL * 50 mL = 50 g

Q = (25.0 ⁰C - 26.7 ⁰C) * 4.184 J/°Cg * 50 g

Q = -349.4 J

ΔH = -349.4 J / 0.025 mol

ΔH = -13974 J/mol = -13.974 kJ/mol

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The time needed to decrease reactant concentration based on its half-life is 68.47 seconds.

We need to know about the half-life of the radioactive elements to solve this problem. The radioactive element will decay over time and follow the equation

N = No(1/2)^(t/t'')

where N is the final quantity, No is the initial quantity, λ is the decaying constant, t is time and t'' is the half-life of a radioactive element.

From the question above, we know that

t'' = 41.3 s

No = 6.5 m

N = 2.06 m

By substituting the given parameters, we can calculate the time taken

N = No(1/2)^(t / t'')

2.06 = 6.5 . (1/2)^(t / 41.3)

0.32 = (1/2)^(t / 41.3)

⁰'⁵log(0.32) = t / 41.3

1.66 = t / 41.3

t = 68.47 seconds

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Answer:

Since there is an equal number of each element in the reactants and products of MgO + 2HBr = MgBr2 + H2O, the equation is balanced.