257Lr has a half-life of 8 seconds. How long will it take for 75% of the sample to decay?

Answer:

B. Because the planet travels slowly when it is far away from the sun

option a,b,c are correct.gather your belongings,turn off all hot plates & other heating apparatus, turn off all water these are options that must be done in case of a fire alarm or other evacuation .

To guarantee your safety, take prompt action when the fire alarm goes off. The fire alarm system was created and constructed to give you a head start so you may safely leave the building in an emergency.Never dismiss a warning or believe it to be fake or the outcome of a test.The nearest and safest exit and/or stairs must be used by everyone to leave the building.Never leave during a fire alarm activation in an elevator.Once outside, make your way away from the structure. Gather on the sidewalk of the building next door or across the street.The firefighters and fire engines will be working in front of the structure. Don't stand in their way as they enter the building.

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Answer:

A. 30cm³

Explanation:

Based on the chemical reaction:

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

1 mol of calcium carbonate reacts with 2 moles of HCl to produce 1 mol of CO₂

To solve this question we must convert the mass of each reactant to moles. With the moles we can find limiting reactant and the moles of CO₂ produced. Using PV = nRT we can find the volume of the gas:

Moles CaCO₃ -Molar mass: 100.09g/mol-

1.00g * (1mol / 100.09g) = 9.991x10⁻³ moles

Moles HCl:

50cm³ = 0.0500dm³ * (0.05 mol / dm³) = 2.5x10⁻³ moles

For a complete reaction of 2.5x10⁻³ moles HCl there are necessaries:

2.5x10⁻³ moles HCl * (1mol CaCO₃ / 2mol HCl) = 1.25x10⁻³ moles CaCO₃. As there are 9.991x10⁻³ moles, HCl is limiting reactant.

The moles produced of CO₂ are:

2.5x10⁻³ moles HCl * (1mol CO₂ / 2mol HCl) = 1.25x10⁻³ moles CO₂

Using PV = nRT

Where P is pressure = 1atm assuming STP

V volume in L

n moles = 1.25x10⁻³ moles CO₂

R gas constant = 0.082atmL/molK

T = 273.15K at STP

V = nRT / P

1.25x10⁻³ moles * 0.082atmL/molK*273.15K / 1atm = V

0.028L = V

28cm³ = V

As 28cm³ ≈ 30cm³

Right option is:

Based in the data provided, the percentage by mass of K2SO4 is 60.55 %.

The mass of K2SO4 in the mixture is obtained from the data given as follows:

Total mass of sample = 0.649 g

Let the mass of K2SO4 in the mixture be X g

Mass (NH4)SO4 = (0.649 - X )g

Moles of K2SO4 = X g/174.25 g/mol

= 0.00574X mol

Moles of (NH4)2SO4 = (0.649 - X)g / 132.13 g/mol

= (0.00491 - 0.00757X) mol

Total number of moles SO42- ions precipitated = 0.00574X mol + (0.00491 - 0.00757X)mol

= (0.00491-0.00183X) mol

Mole ratio of SO42- ions to Ba2+ ions = 1:1

Thus, moles of Ba2+ ions = (0.00491 - 0.00183X)mol

Moles of BaSO4 precipitated = 0.977 g/233.38 g/mol = 0.00419 moles

1 mole of BaSO4 produces 1 mole of Ba2+ ions

Therefore,

(0.00491 - 0.00183X) mol = 0.00419mol

0.00183X = 0.00491 - 0.00419mol

0.00183X = 0.00072

X = 0.00072/0.00183 = 0.393 g

Mass of K2SO4 = 0.393 g

Percentage by mass of K2SO4 = (0.393/0.649) × 100

Percentage by mass of K2SO4 = 60.55 %

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The mass of ASA - Acetylsalicylic acid per tablet is 214.9 mg. The number of moles present in the tablet, is 0.001190.

For this experiment it is important to find the number of moles of ASA present in the solution. By doing this we will get the amount of ASA in the tablet also.

Students prepared a solution by hydrolyzing 0.3219 g of a crushed aspirin tablet in NaOH and then diluting with DI water in a 100-mL volumetric flask.

Number of moles = mass of ASA / molar mass of ASA

The molar mass of ASA = 180.16 g/mol

Therefore, Number of moles = 0.3219 g / 180.16 g/mol

= 0.001785 mol.

Now finding the number of moles present in the tablet,

Moles in tablet = (moles of ASA from solution) x (mass of tablet / mass of solution)

= 0.001785 mol x (0.4267 g / 0.3219 g x 1.50 mL / 50 mL)

= 0.001190 mol

Now finding the mass of ASA,

Mass of ASA per tablet = (moles of ASA in tablet) x (molar mass of ASA)

= 0.001190 mol x 180.16 g/mol

= 0.2149 g or 214.9 mg

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Explanation

Given

Mass of metal = 24.2 g

Initial volume = 15.50 mL

Final volume = 18.4 mL

Volume occupied by metal = 18.4 mL - 15.50 mL = 2.9 mL

Solution

density = mass/volume

density = 24.2g/2.9 mL

density = 8.34 g/mL

Answer

Density of metal = 8.34 g.mL

Answer:

Voltage is the measure of electric potential energy per unit charge, current is the flow of electric charge through a circuit, and resistance is the property of a material that opposes the flow of electric current.

Ohm's Law relates these three concepts by stating that current is directly proportional to voltage and inversely proportional to resistance.

Hope this helps!

In this question, we have the following reaction:

2 Pb + O2 -> 2 PbO

We have to find the percent yield of this reaction, we have:

451.4 grams of Pb

316.9 grams of PbO, this is the actual yield, we will have to find the theoretical yield now

In order to find the theoretical yield, we need to know how many moles of Pb we have in 451.4 grams, the molar mass of Pb is 207.2g/mol

207.2g = 1 mol

451.4 g = x moles

207.2x = 451.4

x = 451.4/207.2

x = 2.18 moles of Pb in 451.4 grams

According to the molar ratio of Pb and PbO, we have the ratio of 2 moles of Pb to form 2 moles of PbO, therefore if we have 2.18 moles of Pb, we will also have 2.18 moles of PbO.

Now we need to find the theoretical mass of PbO, using its molar mass, 223.2g/mol

223.2g = 1 mol

x grams = 2.18 moles

x = 2.18 * 223.2

x = 486.6 grams of PbO is the theoretical yield

Now to find the percent yield, we need to use the following formula:

%yield = (actual yield/theoretical yield)*100

%yield = (316.9/486.6)*100

%yield = 65

The percent yield of this reaction will be 65%

Answer:

The amount of the first solution rick needs to mix together to create the love portion is 8.5 mL

Explanation:

So as to make the love potion, we have;

The percentage of carbonated water in the love portion = 40%

The percentage of green tea in the first solution = 65%

The percentage of carbonated water in the first solution = 15%

The percentage of whole milk in the first solution = 20%

The percentage of orange juice in the second solution = 17%

The percentage of lemonade in the second solution = 38%

The percentage of carbonated water in the second solution = 45%

Let 'x' represent the volume in mL of the first solution added to make the love portion, and let 'y' be the volume in mL of the second solution added to make the love portion, we have;

x + y = 51...(1)

0.15·x + 0.45·y = 0.40×51 = 20.4

0.15·x + 0.45·y = 20.4...(2)

Solving the system of simultaneous equation by making 'y' the subject of each of the equation gives;

For equation (1)

y = 51 - x

For equation (2)

y = 20.4/0.45 - (0.15/0.45)·x = 136 - 3·x

y = 136/3 - (1/3)·x

Equating the two equations of 'y', gives;

51 - x = 136/3 - (1/3)·x

51 - 136/3 = x - (1/3)·x

17/3 = (2/3)·x

(2/3)·x = 17/3

x = (3/2) × (17/3) = 17/2 = 8.5

x = 8.5

y = 51 - x = 42.5

y = 42.5

Therefore, the amount of the first solution rick needs to mix together to create the love portion, x = 8.5 mL

The plum-pudding model suggested a uniform distribution of electrons within a positively charged atom, whereas the Bohr atomic model introduced the concept of quantized energy levels and specific orbits for electrons.

The Bohr atomic model and the plum-pudding model are two distinct models that were proposed to explain the structure of atoms, and they differ in their fundamental concepts.

The plum-pudding model, also known as the Thomson model, was proposed by J.J. Thomson in 1904. According to this model, an atom consists of a positively charged sphere (the "pudding") with embedded negatively charged electrons (the "plums").

In other words, the electrons were thought to be uniformly distributed throughout the positively charged atom. This model suggested that the atom was overall neutral and did not contain any distinct substructures.

On the other hand, the Bohr atomic model, proposed by Niels Bohr in 1913, introduced the concept of quantized energy levels within an atom. According to this model, electrons orbit the nucleus in specific, discrete energy levels or shells.

These energy levels are represented by fixed orbits or paths, with electrons occupying only certain allowed orbits. The model also introduced the idea that electrons can transition between energy levels by emitting or absorbing energy in discrete packets called photons. This model explained phenomena like atomic spectra and the stability of atoms.

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Both changing particle size and adding a catalyst can influence the reaction rate, while adding heat specifically affects the rate by increasing the kinetic energy of the reactant particles.

The correct option are A and C.

Both changing particle size and adding a catalyst can alter the reaction rate.

Changing particle size can affect the reaction rate because it influences the surface area available for the reactant particles to interact. Smaller particle sizes result in a larger surface area, increasing the frequency of collisions between particles and accelerating the reaction. Conversely, larger particle sizes reduce the surface area, leading to fewer collision events and slower reaction rates.

Adding heat can also alter the reaction rate. Increasing the temperature provides more thermal energy to the reactant particles, causing them to move faster and collide with greater energy. This enhanced kinetic energy leads to more successful collisions and an increased reaction rate.

Adding a catalyst can significantly affect the reaction rate. A catalyst provides an alternative reaction pathway with lower activation energy, enabling the reaction to occur more easily. By lowering the energy barrier, a catalyst increases the rate of reaction without being consumed or permanently altered in the process.

The correct option are A and C.

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My classmate's statement in incorrect because plants are also composed of cells.

All living things are composed of cells. A cell is the smallest unit of living organisms. Cells obtain energy via the process of cellular respiration. During cellular respiration, glucose is broken down to yield carbon dioxide and water.

In photosynthesis, carbon dioxide and water are combined to form glucose. The two processes are opposites of each other. Plants produce their own food via photosynthesis. Since plants are composed of cells, plant cells also undergo cellular respiration therefore my classmate's statement in incorrect.

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Chlorofluorocarbons (CFCs) are man-made chemicals containing chlorine and fluorine that cause ozone molecules to break down. Thus, option B is the answer.

Chlorofluorocarbons are non-toxic, synthetic compounds that contain atoms of Chlorine, Fluorine and Carbon. They are commonly used in the manufacture of aerosol sprays and are also used as solvents and refrigerants. CFCs were first introduced in 1928 by General Motors Company for its refrigerators.

While CFCs are very safe to use in most applications and are stable in the lower atmosphere, these chemicals when released to the upper atmosphere can cause significant reactions. CFCs when released into the upper atmosphere can lead to the destruction of the ozone molecules followed by the release of the UV radiation into the atmosphere.

Thus, CFCs are man-made chemicals which cause ozone molecules to break down.

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0.294kg is mass (in kg) that 4.64 moles of Copper have.

The unit of material quantity in the International System of Units is the mole (SI). A substance's quantity determines how many elementary entities of that substance are contained in an object or sample. The number of elementary entities in a mole is precisely 6.02214076 × 10²³.

The amount of a substance in a mole is determined by the mass of a mole of that substance divided by the mass of the substance given in a chemical reaction. The term is also used to express concentration measurements like mole per litre and molecular weight.

m= n × MM

m is mass in grams; n is moles & MM is molecular mass

The molecular mass of copper is 63.546.

We now have all the required information to perform the calculation

m= 4.64 × 63.546

m= 294 g

= 0.294kg

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Answer:

I think it’s D.

Explanation:

Answer:

elements tend not to react with other elements, there were no oxide compounds for Mendeleev to study. –Group 18 elements are generally unreactive. sodium ion is smaller because the sodium atom lost one electron. –An Na+ ion is smaller because it has one fewer electron shell.

Explanation:

can you me as brainliest if its right? i just need a few more to rank up! ^-^

Also have a great day and good luck in your studies!

Answer:

Smartphones use electromagnetic waves to transmit energy and information wirelessly. Specifically, they use radio waves, which are a type of electromagnetic wave that has a long wavelength and low frequency. These waves can travel long distances and can penetrate certain materials like walls and buildings.

Here's a breakdown of how a cell phone sends and receives transmissions:

When it comes to interacting with matter, radio waves can be blocked or weakened by certain materials, such as:

Overall, while smart phones use waves to transfer energy and information wirelessly, there are limitations to their reach and reliability.

Explanation:

It is the motion of particles that creates a form of energy called heat (or thermal) energy that is present in all matter. Tiny particles in solids, liquids and gases are always in motion. It is the motion of particles that creates a form of energy called thermal (heat) energy that is present in all matter.

4.29 g, or % of the reaction's yield. Yield in synthesis reaction percent: 85%. Explanation: C2H5OH+3O22CO2+3H2O is the balanced equation.

Multiply the molal mass of water by the number of moles. 2 + 16 = 18 g/mol is the molar mass. This yields 0.834 moles H2O x 18 g/mol when multiplied by the end result. 15 grams of water equal one gram of H2. For this experiment, 15 grams of water should be produced theoretically.

The percentage and theoretical yield are multiplied together to arrive at the simple calculation for actual yield.

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Answer:

Burning of fossil fuels

Cutting of tress

Also CO2 is produce in industries like cement manufacturing.

Explanation:

The answer is 3) Rock Breaking up due to mechanical force

Hope that help :)

||-//

Answer:

30.0g/mol

Explanation:

Step 1: Given data

Step 2: Calculate the moles of the gas

We will use the ideal gas equation.

\(P \times V = n \times R \times T\\n = \frac{P \times V}{R \times T} = \frac{1atm \times 0.0933L}{\frac{0.0821atm.L}{mol.K} \times 273.15K} = 4.16 \times 10^{-3} mol\)

Step 3: Calculate the molar mass of the gas

4.16 × 10⁻³ moles correspond to a mass of 0.125 g. The molar mass of the gas is:

\(\frac{0.125g}{4.16 \times 10^{-3} mol} =30.0g/mol\)

The molar mass of the 0.125 g  of the gas occupies 93.3 mL at STP is 30.0 g/mol.

Number of moles of Gas at STP,

\(\bold{n =\dfrac {PV}{RT}}\)

where,

P - pressure

V- volume

R- gas constant

T - temperature

Put the values in the formula,

\(\bold{n =\dfrac {1 \times 0.0933} {0.082 \times 273.15 }}\\\\\bold{n =4.16 \timesw 10^-^3}\)

The molar mass of the gas can be calculated using formula,

\(\bold {m = \dfrac {w}{n}}\\\\\bold {m = \dfrac {0.125} {4.16 \times 10^-^3}}\\\\\bold {m = 30g/mol}\)

The molar mass of the 0.125 g  of the gas occupies 93.3 mL at STP is 30.0 g/mol.

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Answer:

B) Mass- I searched it up

Answer:

a.

Explanation:

One double bond.

For example ethene CH2=CH2

Answer:

One mole of ideal gas occupies 22.4L volume at STP

Explanation:

So., we treat carbon dioxide an ideal gas:

3 mol x 22.4L •Mol-¹ ≈? ?L

Answer:

It's because they aren't destroyed they're just rearranged differently to create different products. There's like a name for this. It's something like the law of conservation energy. But the reason is mass cannot be created nor can it be destroyed.

Answer:

Atoms don’t appear or disappear during the reaction. Instead, they get rearranged.

Explanation:

Exact answer from Plato/Edmentum!! :)