the beta decay of cesium-137 has a half-life of 30 years. how many years must pass to reduce a 25 mg sample of cesium 137 to 6.25 mg? responses

Resulting pH = 7.4

Using Henderson Hasselbalch equation,

Since pH = pKa + log([A]/[HA])

8 = 7.4 + log([A]/[HA]), hence [A]/[HA] = 4   .....(i)

0.1 L = 0.1 mole (moles/L), hence [A] +[HA] = 0.1   .......(ii)

using eqn (i) and (ii), [A] = 0.08 moles and [HA] = 0.02 moles

After adding 30 ml of HCL, 0.03 L = 0.03 moles (mole/L)

Since [A] reduces and [HA] increases,

[A] = 0.08 - 0.03 = 0.05 and [HA] = 0.02 + 0.03 = 0.05

So new pH of solution becomes,

pH = 7.4 + log(0.05/0.05) = 7.4

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The chemical change that would provide evidence of exothermic reaction is evolution of heat.

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.

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Answer:

Going down a family means the elements are getting larger.  As more electrons surround the positively charged nucleus, they reduce the attractive electrostatic force because they are further away, and existing electrons repulse them.

Explanation:

Electronegativity is a measure of the attraction an element has for electrons.  Fluorine has a high electronegativity (2.98), while Francium does not (0.7).  Fluorine more readily attracts other electrons.  When going down a family on the periodic table, electronegativity decreases.  This is because the existing electrons have already filled the electron shells closest to the positive nucleus.  A new electron arriving near Francium doesn't experience the full attraction of the nucleus since it so far away.  The existing electrons form a repulsive barrier.



Acid the tendency of an acid to donate a proton. Thus, the more readily a compound donates a proton, the stronger the acid.

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Answer:

1. Creating products that improve people's lives.

2. Remaining impartial about data while conducting experiments.

-22.57 kJ of heat energy will be absorbed when 8.33 grams of NH3 is produced.

To determine the amount of heat energy absorbed or released when 8.33 grams of ammonia (NH3) is produced, we need to use the balanced equation for the reaction and the heat of formation for NH3.

The balanced equation for the production of NH3 is:

N2(g) + 3H2(g) → 2NH3(g)

The heat of formation, or delta Hf, of a substance is the amount of heat absorbed or released when one mole of a substance is formed from its elements at standard conditions. The standard enthalpy of formation (ΔHf°) for NH3 is -46.19 kJ/mol

To find out the amount of heat energy absorbed or released when 8.33 grams of NH3 is produced, we need to know the molar mass of NH3 and use it to convert the mass to moles, then multiply it by the enthalpy of formation.

The molar mass of NH3 is equal to 17 g/mol.

8.33 grams NH3 / 17 g/mol = 0.492 mol NH3

The heat energy absorbed or released when 8.33 grams of NH3 is produced is:

-46.19 kJ/mol * 0.492 mol NH3 = -22.57 kJ

So, -22.57 kJ of heat energy will be absorbed when 8.33 grams of NH3 is produced.

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Water is necessary for life. b) Nearly colorless property of water has the least impact on life

While all of the properties of water are important for life, the property of being nearly colorless is the one that affects life the least. The other properties, such as hydrogen bonding, cohesiveness, high heat capacity, and high heat of vaporization, all play critical roles in the functioning of living organisms and the environment. Hydrogen bonds between water molecules give water its high surface tension, which allows for the cohesion of water molecules that allows for the movement of water in plants, and the cohesion and adhesion property of water that allows for the movement of water in rivers and oceans. High heat capacity and high heat of vaporization are also important for maintaining a stable temperature range for living organisms.

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A chemical compound is a substance formed by the union of two or more chemical elements in a fixed ratio, the union being a chemical bond.

A pure substance is a substance that are made up of only one kind of particle and have a fixed or constant structure. Pure substances are further classified as elements and compounds.

A molecule is the smallest particle of a specific element or compound that retains the chemical properties of that element or compound; two or more atoms held together by chemical bonds.

A mixture is a compound made up of two or more chemical components that are not chemically linked together. This means that a mixture can be made of elements, compounds etc. but not the other way round.

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Basalt is an ingenious salt which is found near the surface. Limestone fossils are found in sedimentary sequences and they are old by 2.7 billion years. Sand stones with trilobites are old about 500 million years.

Rocks are the major parts of the tectonic plates of earth, There are broadly three classes of rocks namely, sedimentary rocks, igneous rocks and metamorphic rocks.

Basalt is a type of well grained igneous rocks found near the surface of earth. Rapid cooling of lava rich in Mg and Ca composes Basalt rock

Limestone, a form of carbonate sedimentary rock composed primarily of calcium carbonate (CaCO3). The minerals calcite and aragonite, which are various crystal forms of CaCO3, make up the majority of its material. When these minerals separate from water that has dissolved calcium, limestone is created.

Sileous sandstone is a typical component of nearshore deposits about 500-600 million years of age. This often grades into siltstone and shale as it moves into the sea, with finer-grained sediment accumulating in deeper water to create these rocks.

Shale rocks with ammonites have an age of about 70 million years. Ammonites are spiral shaped fossilized shells of marine animals.

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We can calculate the number of moles of magnesium that is equivalent to the bromobenzene used:

n_Mg = n_Br * 1.25 = 0.020mol * 1.25 = 0.025mol

Finally, we can calculate the mass of magnesium:

m = n * M

m = 0.025mol * 24.31 g/mol = 0.6 g.

So the mass of magnesium turnings equivalent to the amount of bromobenzene used is 0.6 g.

A molar equivalent is a unit of measurement that corresponds to the number of moles of a reactant that is needed to react with one mole of another reactant.

Bromobenzene is a clear, colorless liquid with a pleasant odor. It is primarily used as a solvent and motor oil additive, and in making other chemicals.

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5.75 moles of water vapor require 2.875 moles of methane, CH4, which is required in a different way.

The moles of CH4 that reacted from the balanced equation will be obtained first.

O2 + CH4 = CO2 + 2H2O

Given the above-mentioned balanced equation,

From 1 mole of CH4, 2 moles of H2O were created.

We can calculate the amount of moles of CH4 required for the reaction using the information above. Details are provided below:

Given the above-mentioned balanced equation,

From 1 mole of CH4, 2 moles of H2O were created.

Therefore,

The formula is: (5.75 1) / 2 = 2.875 moles of CH4 yields 5.75 moles of H2O.

The formula is: (5.75 1) / 2 = 2.875 moles of CH4 yields 5.75 moles of H2O.

In light of this, we can say that 2.875 moles of CH4 are required.

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Moles=Concentration x Volume

Moles = 0.100 x (75/1000) = 0.0075 moles.

We can use the molar mass of AgCl to calculate the mass of AgCl precipitate formed:

Mass of AgCl = moles of AgCl x molar mass of AgCl

mass of AgCl = 0.0075 moles x 143.32 g/mole

mass of AgCl = 1.07 g

It is well verified that AgCl is insoluble in water while NaCl and KCl are soluble. Hence, AgCl is very much less soluble than NaCl or KCl.

The base of silver is weak, whereas chlorine acid is strong. When the weak base responds with a strong acid, it forms acidic salt. It indicates the salt that produces acidic pH, becomes a base when liquefied in water.

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No, it would not be very probable to happen because the first element, neon, is already stable due to the fact that the outermost shell of its atom is completely filled.

An electron that is linked with an atom and that can take part in the development of a chemical bond is referred to as a valence electron. In the formation of a single covalent bond, each of the atoms in the bond contributes one valence electron in order to form a shared pair.

It is possible for the existence of valence electrons to determine the chemical characteristics of an element as well as whether or not it can form bonds with other elements. A valence electron can only exist in the most outer electron shell of an element that is part of the main group.

An atom that has its valence shell completely filled with electrons has a high probability of being chemically inert. A highly reactive atom is one that has one or two valence electrons in excess of what is required for a closed shell. This is because the additional valence electrons can be quickly stripped away to produce a positive ion.

An atom that has one or two valence electrons less than a closed shell is also extremely reactive. This is due to the fact that such an atom has a greater propensity to either gain the missing valence electrons or share valence electrons with neighboring atoms.

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Based on the observed properties of water and rubbing alcohol, the properties of the unknown substance are as follows;

The properties of water are as follows:

The properties of rubbing alcohol are as follows:

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Complete question:

Part A

Water and rubbing alcohol have distinct properties and will react differently with the same substance. Observe these properties of water and rubbing alcohol: color, smell, and ability to dissolve the salt. Record your observations in the table. To observe the solubility of salt in the liquid, put a one-quarter teaspoon of salt into each container and stir. You may weigh out 1.5 g of salt on the electronic balance if you don’t have a one-quarter teaspoon measure.

Part B

Now observe the properties of the liquid in the container labeled unknown. Record the properties of the unknown substance in the table.

Answer:

The separation of sodium and chlorine from sodium chloride

Explanation:

When sodium chloride reacts with water to form the aquated sodium and chloride ions, the entropy increases and thus the reaction is spontaneous

Answer:

a Naturally occurring and stable =

b. naturally occurring and radioactive

If purple flowers are dominant in a plant and white flowers are recessive in that plant, then when purple-flowered plants with two dominant genes are mated with white-flowered plants with two recessive genes, the first generation of offspring should have 100% purple flowers. Therefore, option D is correct.

In genetics, dominance occurs when one variant of a gene on a chromosome masks or overrides the effect of another variant of the same gene on the opposite copy of the chromosome.

The first variant is called dominant, while the second is called recessive. When there is dominance, it is always expressed. When no dominant genes are present, recessive genes are expressed.

Purple-flowered plants with two dominant genes should produce 100% purple flowers in the first generation when mated with white-flowered plants with two recessive genes.

The attached Punnett square shows the above combination.

Thus, option D is correct.

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We would need to measure  25.5 g of the potassium hydrogen phthalate an d make up to  500cm³ mark.

We know that we can be able to prepare a chemical if we can be able to measure out a given mass of the chemical that is in question and then make up to the mass that we need.

In the case of the  Potassium hydrogen phthalate  that we have;

Number of moles to be prepared = concentration * volume

= 0.25 mol/dm³ * 500/1000 L

= 0.125 moles

Mass of the compound = Molar mass * Number of moles

= 0.125 moles * 204 g/mol

= 25.5 g

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Solids have a fixed volume as well as a fixed shape. Liquids have a fixed volume but liquids do not have a fixed shape. Gases do not have a fixed volume or a fixed shape and take up the shape and volume of the container they are placed in due to the weak intermolecular forces of attraction.

Among the three states of matter, solids have the most rigid structure. This is because solids have the strongest intermolecular forces of attraction amongst them and have a fixed shape as well as volume.

Among solids, liquids and gases, liquids have intermediate forces of attraction and hence they have a fixed volume but not a fixed structure and hence they take the shape of the container in which they are kept.

Particles of gases have the weakest intermolecular forces of attraction and hence they have no fixed volume or fixed shape and hence gases take up both the shape as well as the volume of the container they are kept in.

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Aluminum + hydrochloride acid yield aluminum chloride + hydrogen gas therefore the balanced equation is 2Al+6HCl→2AlCl₃+3H₂.

This is referred to as the process in which one or more substances which are called the reactants, are converted to one or more different substances known as the products and it involves the exchange of electrons between elements.

In this scenario, when Aluminum and hydrochloride acid reacts they form aluminum chloride and hydrogen gas which is the product and the equation can be seen above.

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Explanation:

This is answer is given the following

The energy that is stored in the spring is 2.94 J.

We have to note that the elastic potential energy of the spring is the energy that has been stored in the spring and it is released to be able to do work once we pull the spring.

In this case we already know that;

W = 1/2Ke^2

W = work done

K = force constant

e = extension

Thus;

W = 0.5 * 3 * 1.4^2

W = 2.94 J

We can see that the stored energy for the spring in question is 2.94 J of energy stored.

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A molecule will always be polar if it has polar bonds.

For a molecule to be polar, it must have polar bonds and have those bonds organized in such a way that the bond dipoles do not cancel each other out. Molecules that are polar have both positively and negatively charged parts. A common polar substance is water. Because of its structure and the types of bonds it contains, the molecule has a slight positive charge at one end (the hydrogen end) and a slight negative charge at the other (the oxygen end). Due to the uneven distribution of electrons among the atoms and the asymmetrical nature of the water molecule, the hydrogen atoms at one pole of the molecule are positively charged, while the oxygen atoms at the other pole are negatively charged (side). We use the term "electrically polar" to describe the water molecule.

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If the scientist repeats the experiment using lower concentrations of lead than those she used initially, she can draw several conclusions based on the results of the experiment.

If she finds that the results are similar or the same as her initial experiment, she can conclude that the effect observed in her initial experiment is likely due to the lead and not a result of chance. This would provide support for her hypothesis that lead is responsible for the observed effect. Additionally, this could also indicate that the effect is likely to be present at a wide range of lead concentrations, and not just at the higher concentrations used in the initial experiment. If the results are different, however, she may conclude that the effect is dependent on the concentration of lead and that lower concentrations have a weaker effect.   For example, she may have used different methods for preparing the lead solutions in the repeat experiment which could have led to variations in the final concentrations.

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More stability is demonstrated by [Fe(C). 2 \s​ \s O \s4 \s​ \s ] \s3− In comparison to non-chelates, metal chelates are more stable. Oxalate produces metal chelates.

stability and is a bidentate ligand. Because of this, [Fe(C 2 O 4 ] 3 is more stable.the four Spartan files is most likely to be the best approximation of the actual complex, SEFeox3LS, SEFeox3HS, B3LYPFeox3LS, or B3LYPFeox3HS. Open that file the one deemed to be the most stable spin case of Fe ( ox ) 3 − 3 in the previous . Go to the Setup window and choose Calculations. Click the boxes next to Infrared Spectra and Vibrational Modes. The calculation time will depend on the processor in the computer, but may need to run overnight [Co(en)3] [Co(NH3)6] is less stable than 3+. As [Co(en)3], 3+ Due to the presence of the bidentate ligand, ethylene diamine, 3+ is a metal chelate. Comparatively speaking, monodentate lignad-only complexes are less stable than metal chelates.

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The complete chemical formula for the unknown compound P₄Sₓ  is  P₄S₆.

The given unknown compound has the formula P₄Sₓ , where P stands for phosphorus and S stands for sulphur. "X" stands for a whole number which denotes the number of sulphur atoms in the compound.

To determine the value of "X" we need to know the ratio between P and S. There are 4 phosphorus atoms present in the compound.

Since it is given that, we have 6.3 moles of phosphorus(P) and 9.4 moles of sulphur (S). In order to express this in terms of 1, we can divide both sides by 6.3 moles to get a ratio of 1 to 1.5

P= 6.3/6.3= 1

S= 9.4/6.3=1.5

This implies, for every 1 P, there is 1.5 S . So, for 4 P we get;

P= 1× 4= 4

S= 1.5× 4= 6

Thus, for every 4 P we will have 6 S.

Hence, the complete chemical formula is P₄S₆.

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Answer: Neutron

Explanation:

Protons have a positive charge (+).

Electrons have a negative charge (-).

Neutrons have no charge.

Minerals is required for a fossil to become petrified.The preserved remains, or signs of remains, of extinct animals are called fossils.

The remnants of the creature itself are not fossils! They're stones. An full organism or only a portion of one can be preserved as a fossil. Leaves, feathers, shells, bones, and shells may all turn into fossils. Fossils come in a wide range of sizes. Only a microscope can see microfossils. Microfossils include pollen and bacteria. Petrified trees or dinosaur bones are examples of macrofossils. Once preserved remains have aged 10,000 years or more, they are considered fossils. Deep underground rock formations are a common place to find fossils. Through replacing the original material and filling the original pore spaces with minerals, petrification is the process by which biological material turns into a fossil.

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The structural formula of 4,4-dimethyl pent-2-ene is:

H3C-CH2-CH(CH3)-CH(CH3)-CH2-CH3.

This molecule contains a pent-2-ene chain which is composed of 5 carbon atoms and 2 double bonds with a methyl group (-CH3) attached to the 4th and 5th carbon atoms. The structural formula of 4,4-dimethylpent-2-ene represents the arrangement of atoms in the molecule using chemical symbols and bond lines.

The chemical symbol for carbon is "C" and for hydrogen is "H". In this structural formula, you can see that there are 5 carbon atoms (C) and 14 hydrogen atoms (H) in the molecule.

The line (-) represents a single bond, which is a covalent bond between two atoms. The double bond is represented by "=".

The molecule contains a pent-2-ene chain which is composed of 5 carbon atoms and 2 double bonds between the 2nd and 3rd and 4th and 5th carbon atoms. The molecule also contains two methyl groups (-CH3) attached to the 4th and 5th carbon atoms. A methyl group is a functional group that contains one carbon atom and three hydrogen atoms.

This structural formula is a way to represent the molecular structure of 4,4-dimethyl pent-2-ene in a simplified way.

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