Select the correct answer.
Why is it important for scientists to keep testing a hypothesis even after they’ve found it to be true?

A.
Repeated tests help determine whether the hypothesis is always true in different circumstances.
B.
Experiments are rarely accurate, so it’s important to keep testing a hypothesis.
C.
Scientists can learn experimental procedures through repeated testing of a hypothesis.
D.
Repeatedly testing a hypothesis qualifies it to be accepted as a theory.

Based on the given reaction, the acid-base pairs in this reaction are:

An acid-base pair refers to a set of two chemical species that are related through the transfer of a proton (H+ ion) during a chemical reaction.

One species acts as an acid by donating a proton, while the other acts as a base by accepting that proton.

In the given reaction:

HCO₃⁻ (aq) + NH₃ (aq) → NH₄⁺ + CO₃²⁻

An acid-base pair can be identified as follows:

HCO₃⁻ (bicarbonate ion) can act as an acid by donating a proton (H⁺), becoming CO₃⁻.

NH₃ (ammonia) can act as a base by accepting a proton (H⁺), becoming NH₄⁺ (ammonium ion).

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Answer:

B

Explanation:

Because the atomic mass is the mass of a single atom of a chemical elements

Answer:

The third option

Explanation:

This reaction is a single replacement reaction because K replaced Mg and a redox reaction because the ion charges of the elements changed from a 0 charge on K to +1 charge, and a +2 charge on Mg to a 0 charge.

The two functional groups that the aminoacid has according to the picture are amine and carboxyl.

In chemistry and related areas, a functional group can be defined as a group of atoms bonded in a specific molecule that can affect the was the molecule reacts or the specific behavior of it.

In the case of the molecule presented, which is an amino acid, two functional groups can be identified:

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There are numerous ways to determine whether lead is present in an ore. Atomic absorption spectroscopy is a popular approach. With this method, an ore sample is dissolved in acid and then atomized in a flame or plasma.

The sample's atoms will absorb light at particular wavelengths that are peculiar to the element under investigation. The amount of light absorbed can be used to calculate how much lead is present in the sample. Inductively coupled plasma mass spectrometry and X-ray fluorescence spectroscopy are further techniques. It is crucial to remember that these procedures call for specialized tools and training, thus they ought to only be carried out in a lab by qualified experts.

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There are approximately 1.765 x 10²³ molecules of KCl in 21.89 grams of KCl.

Potassium chloride (KCl) is a compound made up of potassium and chloride ions. It is a colorless, odorless salt that is commonly used in a variety of applications.

Molar mass of KCl is 74.55 g/mol; number of moles = Mass/ Molar mass

So, the number of moles = 21.89 g ÷ 74.55 g/mol = 0.2936 mol

and the number of molecules = Number of moles * Avogadro's number

Number of molecules = 0.2936 mol x 6.02 x 10²³ molecules/mol

Number of molecules = 1.765 x 10²³ molecules

Therefore, there are approximately 1.765 x 10²³ molecules of KCl in 21.89 grams of KCl.

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Answer:

100N

Explanation:

F=20kg•5ms^-2

F=100N

Answer:B

Explanation:

The mean of the data set is approximately 4.0626, and the 90% confidence interval is [4.060925, 4.064275].

The sample mean (x) is calculated as follows:

x = (4.0620 + 4.0550 + 4.0650 + 4.0740 + 4.0550 + 4.0660) / 6

x ≈ 4.0626 (rounded to four decimal places)

The 90% confidence interval is calculated as follows;

Standard deviation (s):

(4.0620 - 4.0626)² = 0.00000036

(4.0550 - 4.0626)² = 0.00000576

(4.0650 - 4.0626)² = 0.00000006

(4.0740 - 4.0626)² = 0.00001328

(4.0550 - 4.0626)² = 0.00000576

(4.0660 - 4.0626)² = 0.00000012

average of the squared differences:

(0.00000036 + 0.00000576 + 0.00000006 + 0.00001328 + 0.00000576 + 0.00000012) / 6 ≈ 0.00000624

s = √(0.00000624)

s ≈ 0.002496

the standard error of the mean (SEM):

SEM = 0.002496 / √6

SEM ≈ 0.001018

For a 90% confidence interval, the z value is approximately 1.645.

ME = 1.645 * 0.001018 ≈ 0.001675

CI = x ± ME

CI = 4.0626 ± 0.001675

CI ≈ [4.060925, 4.064275]

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Answer:

specific heat, the quantity of heat required to raise the temperature of one gram of a substance by one Celsius degree. The units of specific heat are usually calories or joules per gram per Celsius degrees.

Explanation:

the heat required to raise the temperature of the unit mass of a given substance by a given amount (usually one degree).

Answer:

Top Left

Explanation:

Homogeneous means that the letters should be the same (this rules out bottom left and top right). Dominant genes are represented by capital letters, so this leaves only the top left as the correct answer

Answer:

The weight of an object is defined as the force of gravity on the object and may be calculated as the mass times the acceleration of gravity, w = mg.

Explanation:

The measurement of the effect of gravity on an object's mass is called weight. While mass m is a measurement of the object's amount of matter. W=mg provides the weight.

The formula W (weight) = m (mass) times g (gravity, on Earth typically measured at 9.8 N/kg) allows you to determine something's weight from its mass and vice versa.

The common weight calculation formula is W = mg (N/kg). Here, "g" stands for the acceleration brought on by gravity. The value of g on earth is 9.8 m/s2. Other names for it include the gravitational constant.

A body's mass, which is a measurement of how much matter it contains, is equal to its weight when multiplied by the acceleration caused by gravity. The SI unit of weight is the Newton, and the SI unit of mass is the kilogramme (kg) (N).

Thus,The formula relating mass and weight is W=mg.

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The strand 1 of hydrocarbons is used to produce plastic, hence option D is correct.

Raw resources like natural gas, oil, or plants that have been processed into ethane and propane are used to make plastics. The subsequent "cracking" procedure uses heat to transform ethane and propane into ethylene and propylene. To produce various polymers, these components are mixed.

Propylene is a substance found in large quantities in petroleum. In order to speed up chemical processes, refiners combine heated propylene with a catalyst to create plastic. Propylene molecules start to cluster together like beads on a thread as a result.

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Answer:

1:aerobic

2:anaerobic

3:aerobic

Heat is added to ice at 0 °C. Explain why the temperature of the ice does not change. What does change?When heat is added to ice at 0°C, the temperature of the ice does not change. This happens because all the heat energy is used up in overcoming the intermolecular forces of attraction (hydrogen bonds) that exist between the water molecules in ice.

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Answer:

The heat Q transferred to cause a temperature change depends on the magnitude of the temperature change, the mass of the system, and the substance and phase involved. (a) The amount of heat transferred is directly proportional to the temperature change.

Hope it helps, BE SAFE! :3

The partial pressure of O2 in the gas mixture is 7.91 atm.

Using the ideal gas law, PV = nRT, the total number of moles of gas in the mixture would be:

Moles of N2 in the mixture = 0.270 x 0.560 = 0.1512 mol

Moles of CO2 in the mixture: n = PV/RT

                          = 0.350x2/0.0821 x273

                          = 0.00498 mol

Moles of O2 = Total moles - moles of N2 - moles of CO2

                     = 0.560 mol - 0.1512 mol - 0.00498 mol

                      = 0.404 mol

Now we can use the ideal gas law to find the partial pressure of O2:

P = nRT/V

  = (0.404)(0.0821)(273) / 2

  = 7.91 atm

Therefore, the partial pressure of O2 in the mixture is 7.91 atm.

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Answer: A. 11.43 g Al

Explanation:

To solve this problem, we need to use the process of dimensional analysis, which essentially turns all of the values into fractions that will cancel out units. We always start by using what we are given and then set up the units so that everything cancels besides what we need to solve for.

given Al2O3 g * (1molAl2O3/mass Al2O3 for periodic table) * (Al mole ratio from balanced equation / Al2O3 mole ratio from the balanced equation) * ( Al mass from periodic table / 1 mol Al)

Now, I will plug all values in and solve.

21.6 gAl2O3 * (1molAl2O3/ 101.96 g Al2O3) * (4 mol Al / 2 mol Al2O3) * (26.98 g Al / 1 mol Al)

Now, multiply across the numerator and denominator separately and then proceed with division.

11.43 g Al

Hope this helps!

Answer:

The mass of board is 1.52 g.

Explanation:

Given data:

Density of wood = 0.487 g/cm³

Length of board = 3.21 cm

Width of board = 12.2 cm

Height of board = 0.80 mm (0.80/10=0.08 cm)

Mass of board = ?

Solution:

We know that density of an object is equal to the mass of substance divided by its volume. So we can calculate the mass from density formula.

Formula:

D = m/v

d = density

m = mass

v = volume

Now we will calculate the volume first.

V = length × width × height

V = 3.21 cm × 12.2 cm × 0.08 cm

V = 3.13cm³

Now we will calculate the mass.

D = m/v

0.487 g/cm³ = m/ 3.13 cm³

m = 0.487 g/cm³ × 3.13 cm³

m = 1.52 g

The mass of board is 1.52 g.

Answer:

6.25e-6 is the value of the equilibrium constant

Explanation:

we have this equation

\(PbBr(s) ----- Pb^{2+}(aq) + 2Br(aq)\)

When at a state of equilibrium,

we have the concentration of Pb^2+ to be 0.01

we have the concentration of Br^- to be 0.025

the equilibrium constant concentration of both pure solids and liquid s are said to be equal to 1

[PbBR2] = 1

such tht

Keq = [Pb^2+] x [Br-]^2

we already know the values of these from the above.

0.01x0.025^2

= 0.01 x 0.000625

= 0.00000625

= 6.25 x 10^-6

= 6.25e^-6

The value of S2 is S₂ = 2.1 g/L.Approximately 2.1 g of the gas will dissolve in 2 L of water at 0.6 ATM, assuming the temperature remains constant.

To determine the amount of gas that will dissolve in 2 L of water at 0.6 ATM, we can use Henry's law, which states that the solubility of a gas is directly proportional to the partial pressure of the gas above the liquid.

According to Henry's law, the solubility of a gas can be represented as:S₁/P₁ = S₂/P₂,,where S₁ and S₂ are the solubilities of the gas at the respective pressures P₁ and P₂.Given that 7 g of the gas dissolves in 1 L of water at 2.0 ATM, we can consider this as our initial condition, denoted by S₁/P₁.

Now, we need to find the solubility at 0.6 ATM in 2 L of water, denoted by S₂/P₂.Since the temperature remains constant, we can assume that the solubility of the gas does not change. Therefore, we can rewrite the equation as:

S₁/P₁ = S₂/P₂,

Substituting the known values, we have:

(7 g/1 L)/(2.0 ATM) = S₂/(0.6 ATM),

Solving for S₂, we get:

S₂ = (7 g/1 L) * (0.6 ATM)/(2.0 ATM),

S₂ = 2.1 g/L.

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Answer:

The second period starts with Lithium and Beryllium which have 3 and 4 electrons and hence the last electrons enter the level 2s and they have an electronic configuration of 1s22s1 and 1s22s2

Answer:

The types of energy that are involved in a chemical reaction are :

(A) Activation Energy

(B) Chemical Energy.

- The energy required for a chemical reaction to take place is known as the activation energy. - If the energy is less than the activation energy, the reaction will not take place.

Answer:

A.) 1

Explanation:

Propane only exists in one conformation. It does not have enough carbons to form branches, and there are only hydrogens attached to each carbon. Furthermore, there is no way to twist the carbon or change its orientation (ex. cis- and trans-) to result in a different structure of propane. There is no other way to represent the molecule without drawing a different molecule.

Answer:

According to Coulomb’s law, the electric force between two identical negative charges is inversely proportional to the square of the distance between them. This means that as the distance between the two charges decreases, the electric force between them will increase. Since the charges are both negative, they will repel each other, so as they move closer together, the repulsive force between them will become stronger.

Explanation:

Among electromagnetic waves, UV rays are most dangerous because exposure to these radiation cause serious problems in living organism. Therefore, 4.28×10⁻¹⁹J is the energy of a photon that emits a light frequency of  6.67×10⁻³⁴ Hz.

Electromagnetic wave is a wave which contain two component one is electric component and other is magnetic component. The electric and magnetic component are perpendicular to each other. There are so many wave that comes under electromagnetic wave like infrared wave , radio wave.

There is a relation between energy of wave. frequency of wave, and wavelength of wave

Mathematically,

E=h×ν

where,

E = energy of electromagnetic wave =?

h is planks constant having value 6.67×10⁻³⁴js

ν= frequency of photon=6.42X10¹⁴ Hz

Substituting all the given values in the above equation, we get

E= 6.67×10⁻³⁴×6.42X10¹⁴

E=4.28×10⁻¹⁹J

Therefore, 4.28×10⁻¹⁹J is the energy of a photon that emits a light frequency of  6.67×10⁻³⁴ Hz.

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Answer:

approximately 251.55 grams of AuCl3 would contain 5.0 x 10^23 molecules.

Answer:

18 kJ/mol

Explanation:

Sorry, I could not place a picture so I put it in as a PDF.

Activation energy for reverse = 154 kJ/mol (same as forward due to transition state equivalence).

In a reversible reaction like N₂O₅(g) ⇌ N₂(g) + NO₃(g), the activation energy for the forward and reverse reactions can be equal when the transition states are equivalent. This occurs if the same bonds are broken and formed in both directions.

Given activation energy (Ea) for the forward reaction = 154 kJ/mol and overall energy change (ΔE) = 136 kJ/mol.

For the forward reaction:

Activation energy (Ea_forward) = 154 kJ/mol.

For the reverse reaction, we use the relationship between activation energy and overall energy change:

Ea_reverse = ΔE - Ea_forward

Ea_reverse = 136 kJ/mol - 154 kJ/mol

Ea_reverse = -18 kJ/mol.

However, activation energies are typically reported as positive values. Since a negative activation energy doesn't make physical sense, it suggests that the forward and reverse transition states are structurally similar, making Ea_reverse the same as Ea_forward, which is 154 kJ/mol.

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