The student conducts an experiment to determine the composition of a mixture of nahco3 and na2co3. the student places a sample of the mixture into a preweighted test tube that is attached to container that holds a drying agent. answer

Final answer:

When magnesium ribbon burns with oxygen, it forms a bright, white light and a white, powdery product called magnesium oxide (MgO).

Explanation:

When magnesium ribbon burns with oxygen, it forms a bright, white light and a white, powdery product called magnesium oxide (MgO). The chemical equation for this reaction is:

2Mg (s) + O₂(g) → 2MgO (s)

This is an example of a combination reaction where an element (magnesium) combines with oxygen to form an oxide. The reaction is accompanied by the release of heat and light.

First we determine the moles CaCl2 present:

525g / (110.9g/mole) = 4.73 moles CaCl2 present 

Based on stoichiometry, there are 2 moles of Cl for every mole of CaCl2:
(2moles Cl / 1mole CaCl2) x 4.73 moles CaCl2 = 9.47 moles Cl 

Get the mass:
9.47moles Cl x 35.45g/mole = 335.64 g Cl

Answer: Option (d) is the correct answer.

Explanation:

When atoms of a substance are strongly held together due to strong intermolecular forces of attraction then the substance acquires a fixed shape and volume.

Hence, the substance becomes hard in nature.

For example, solids are hard in nature due to the strength of chemical bonds between its atoms which are held by strong intermolecular forces of attraction.

Whereas in liquids, molecules are held by less strong intermolecular forces of attraction. As a result, they do not have fixed shape and volume.

Thus, we can conclude that hardness is related to strength of chemical bonds.

Acetylene has a chemical formula which can be written as:

C2H2

We can see that there are two positive ions, H+. Now what deprotonation means is that the H+ is removed from acetylene to form acetylene ion and water. In this case, I believe that the answer would be:

LiOCH3

LiOCH₃ would not effectively deprotonate acetylene

The equilibrium reaction can be determined if the pKa or Ka values ​​of the acid and conjugate acids (acids in the product) are known.

So it can be concluded that the reacting acid can protonate the base or vice versa base compounds can deprotonating the acid in the reaction, so that the reaction can proceed to the right to form a product or not

In an acid-base reaction, it can be determined whether or not a reaction occurs by knowing the value of pKa or Ka from acid and conjugate acid

Acids and bases according to Bronsted-Lowry

If the acid gives (H⁺), then the remaining acid is a conjugate base because it accepts protons. Conversely, if a base receives (H⁺), then the base is formed can release protons and is called the conjugate acid from the original base.

The value of the equilibrium constant (K)

Can be formulated:

K acid-base reaction = Ka acid on the left / K acid on the right.

or:

pK = acid pKa on the left - pKa acid on the right

K = equilibrium constant for acid-base reactions

pK = -log K

[tex]\large{\boxed{\bold{K\:=\:10^{-pK}}}}[/tex]

K value> 1) indicates the reaction can take place, or the position of equilibrium to the right.

There is some data that we need to complete from the problem above, the pKa value of the conjugated acid from the base of the compounds above

Whereas the pKa of Acetylene (C₂H₂) itself is = 25

From the conjugated acid pKa value of some of the bases above shows only LiOCH₃ bases that cannot deprotonate acetylene because the pKa value is smaller than the pKa acetylene

The reactions that occur are:

LiOCH₃ + HC ≡ CH ---> HOCH₃ + LiC = CH

The value of the equilibrium constant K is

pK = pKa acetylene - pKa HOCH₃

pK = 25-16

pK = 9

[tex]K\:=\:10^{-pK}[/tex]

[tex]K\:=\:10^{-9}[/tex]

K values ​​<1 indicate a reaction cannot occur

the lowest ph

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the concentrations at equilibrium.

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the ph of a solution

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Keywords : pKa,  acetylene, deprotonate, the conjugate acid

A helium blimp containing 535 kg of helium has approximately 8.05 × 10¹⁸ helium atoms, calculated by dividing the mass by the molar mass of helium and then multiplying by Avogadro's number.

To determine how many helium atoms are in a helium blimp containing 535 kg of helium, we need to use Avogadro's number and the molar mass of helium. First, we find the number of moles of helium:

Mass of helium (m) = 535 kg = 535,000 g
Molar mass of helium (M) = 4.0026 g/mol

Number of moles (n) = m / M = 535,000 g / 4.0026 g/mol ≈ 133786.85 mol

Avogadro's number (N₀) = 6.02214076 × 10²³ atoms/mol

Number of helium atoms = n × N₀ ≈ 133786.85 mol × 6.02214076 × 10²³ atoms/mol ≈ 8.05 × 10²⁸ atoms

Therefore, a helium blimp containing 535 kg of helium has approximately 8.05 × 10²⁸ helium atoms.

Final answer:

To find the weight in kilograms of a balsa wood piece measuring 4.0 inches by 6.0 inches by 20.0 inches, we calculate its volume, apply the given density to find the weight in pounds, and then convert that to kilograms, resulting in approximately 0.980 kilograms.

Explanation:

To calculate the weight of a piece of balsa wood in kilograms, we first need to find its volume in cubic feet and then use the given density to find its weight in pounds. Afterward, we convert that weight to kilograms. The volume is the product of length, width, and height which must be converted from inches to feet (1 inch = 1/12 feet).

Thus, the volume V is calculated as follows:
V = (4.0 inches / 12 inches/foot) × (6.0 inches / 12 inches/foot) × (20.0 inches / 12 inches/foot) = (0.333 feet) × (0.5 feet) × (1.666 feet) = 0.277 cubic feet.

The weight W in pounds is given by the product of the volume V and the density D:
W = V × D = 0.277 cubic feet × 7.8 pounds/cubic foot = 2.161 pounds.

To convert the weight to kilograms, we use the conversion factor 1 pound = 0.453592 kilograms:
Weight in kilograms = 2.161 pounds × 0.453592 kilograms/pound = 0.980 kilograms.

3H2 + N2 ........> 2NH3

This means that each 6 grams of hydrogen react with 28 grams of nitrogen. To know how many grams of nitrogen are required to react with 2 grams of hydrogen, we will simply do cross multiplication as follows:

mass of nitrogen = (2 x 28) / 6 = 9.334 grams

Therefore, if we have 11.3 grams of nitrogen, 9.334 grams would react with 2 grams of hydrogen.

remaining mass of nitrogen = 11.3 - 9.334 = 1.966 grams

Atomic Number is the same as the number of protons in an element.
Mass Number is the number of Protons + Neutrons in an element.

Atomic Number: 6 means 6 Protons
Mass Number: 15 means 15 atoms that are a proton/neutron.
We are given out of the 15 atoms, 6 of them are protons, so the other 9 must be Neutrons.

15 - 6 = 9 so there must be 9 Neutrons.

There are 9 Neutrons in atom's nucleus.

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After a balanced neutralization reaction between Sr(OH)2 and HNO3, the unused Sr(OH)2 determines the solution is basic.

To address this question, let's first write down the balanced equation for the reaction between strontium hydroxide (Sr(OH)2) and nitric acid (HNO3) which is:

Sr(OH)2 (aq) + 2HNO3 (aq) → Sr(NO3)2 (aq) + 2H2O (l)

Now let's calculate the moles of HNO3 added:

Volume of HNO3 = 55.0 mL = 0.055 L

Concentration of HNO3 = 0.200 M

Moles of HNO3 = Volume × Concentration = 0.055 L × 0.200 M = 0.011 mol

Next, calculate the moles of Sr(OH)2:

Mass of Sr(OH)2 = 15.0 g

Molar mass of Sr(OH)2 = 121.63 g/mol (approximately)

Moles of Sr(OH)2 = Mass ÷ Molar mass = 15.0 g ÷ 121.63 g/mol = 0.123 mol

According to the stoichiometry of the balanced equation, we need twice as many moles of HNO3 to react completely with Sr(OH)2. In this scenario, we have excess Sr(OH)2 (0.123 mol) compared to HNO3 (0.011 mol). Hence, all of the HNO3 will react, leaving some Sr(OH)2 unreacted.

After reaction, moles of Sr(OH)2 remaining = 0.123 mol - (0.011 mol × 1/2) = 0.1175 mol

The concentration of remaining Sr(OH)2 can be calculated by assuming the final volume is the sum of the volumes of the solutions mixed, which is an approximation for dilute solutions.

Since all the HNO3 has reacted, the resulting solution will be basic due to the excess Sr(OH)2 remaining.

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(a) The balanced equation for the reaction between the solutes is: [tex]\text{Sr(OH)}_2(aq) + 2\text{HNO}_3(aq) \rightarrow \text{Sr(NO}_3\text{)}_2(aq) + 2\text{H}_2\text{O}(l)[/tex]. (b) The concentrations of ions are: Sr²⁺ is 2.136 M, NO₃⁻ is 0.2 M, and OH⁻ is 4.272 M. (c) Resultant solution is basic in nature.

To solve the given problem, let's follow the steps one by one:

(a) Write a balanced equation for the reaction that occurs between the solutes.

Strontium hydroxide Sr(OH)₂ reacts with nitric acid HNO₃ to form strontium nitrate Sr(NO₃)₂ and water:

[tex]\text{Sr(OH)}_2(aq) + 2\text{HNO}_3(aq) \rightarrow \text{Sr(NO}_3\text{)}_2(aq) + 2\text{H}_2\text{O}(l)[/tex]

(b) Calculate the concentration of each ion remaining in solution.

1. Determine the moles of each reactant:

- Moles of Sr(OH)₂:

[tex]\text{Molar mass of Sr(OH)}_2 = 87.62 \, (\text{Sr}) + 2 \times 16.00 \, (\text{O}) + 2 \times 1.01 \, (\text{H}) = 121.64 \, \text{g/mol} \\\\\text{Moles of Sr(OH)}_2 = \frac{15.0 \, \text{g}}{121.64 \, \text{g/mol}} \approx 0.123 \, \text{mol}[/tex]

- Moles of HNO₃:

[tex]\text{Molarity of HNO}_3 = 0.200 \, \text{M} \\\\\text{Volume of HNO}_3 = 55.0 \, \text{mL} = 0.055 \, \text{L} \\\\\text{Moles of HNO}_3 = 0.200 \, \text{mol/L} \times 0.055 \, \text{L} = 0.011 \, \text{mol}[/tex]

2. Determine the limiting reactant:

According to the balanced equation, 1 mole of Sr(OH)₂ reacts with 2 moles of HNO₃. Therefore, the reaction requires:

[tex]\text{Moles of HNO}_3 \text{ required} = 0.123 \, \text{mol Sr(OH)}_2 \times 2 = 0.246 \, \text{mol}[/tex]

Since we only have 0.011 moles of HNO₃, it is the limiting reactant.

3. Calculate the remaining moles of Sr(OH)₂:

[tex]\text{Moles of Sr(OH)}_2 \text{ reacted} = \frac{0.011 \, \text{mol HNO}_3}{2} = 0.0055 \, \text{mol} \\\\\text{Remaining moles of Sr(OH)}_2 = 0.123 \, \text{mol} - 0.0055 \, \text{mol} = 0.1175 \, \text{mol}[/tex]

4. Determine the concentrations of ions in the solution:

- Volume of the final solution = volume of HNO₃ + volume of water from Sr(OH)₂ dissolution (approximately equal to volume of water added):

Assuming the solution volume remains approximately 55.0 mL + a negligible volume from Sr(OH)₂, the final volume is roughly  0.055 L.

- Concentration of Sr²⁺ ions:

Since only 0.0055 moles of Sr(OH)₂ reacted to form Sr(NO₃)₂, 0.1175 moles of Sr(OH)₂ remain, giving the concentration of Sr²⁺:

[tex]\text{Concentration of Sr}^{2+} = \frac{0.1175 \, \text{mol}}{0.055 \, \text{L}} \approx 2.136 \, \text{M}[/tex]

- Concentration of NO₃⁻ ions:

All HNO₃ dissociates, producing:

[tex]\text{Concentration of NO}_3^{-} = \frac{0.011 \, \text{mol}}{0.055 \, \text{L}} = 0.2 \, \text{M}[/tex]

- Concentration of OH⁻ ions:

From Sr(OH)₂, OH⁻ concentration:

[tex]\text{OH}^{-} \text{ from Sr(OH)}_2: \text{2 moles OH}^{-}\text{ per mole of Sr(OH)}_2 \\\\\text{Concentration of OH}^{-} = 2 \times \frac{0.1175 \, \text{mol}}{0.055 \, \text{L}} \approx 4.272 \, \text{M}[/tex]

(c) Is the resultant solution acidic or basic?

To determine if the solution is acidic or basic, we compare the concentrations of H⁺ and OH⁻. Since HNO₃ (a strong acid) was completely neutralized and excess Sr(OH)₂ (a strong base) remains, the solution will be basic due to the presence of significant OH⁻ ions.

Summary

- Balanced equation:

[tex]\text{Sr(OH)}_2(aq) + 2\text{HNO}_3(aq) \rightarrow \text{Sr(NO}_3\text{)}_2(aq) + 2\text{H}_2\text{O}(l)[/tex]

- Concentrations of ions in solution:

[tex]\text{Sr}^{2+}: 2.136 \, \text{M} \\\\ \text{NO}_3^{-}: 0.2 \, \text{M} \\\\ \text{OH}^{-}: 4.272 \, \text{M} \\\\[/tex]

- Resultant solution is basic due to the presence of excess OH⁻ ions.

This question involves calculating the volume of 95% ethyl alcohol needed to dissolve 0.1 g of sulfanilamide at 78°C and the remaining amount dissolved at 0°C, but these calculations depend on the solubility information of sulfanilamide in ethyl alcohol at these temperatures.

To calculate how much 95% ethyl alcohol is required to dissolve 0.1 g of sulfanilamide at 78°C, you would need to know the solubility of sulfanilamide in the alcohol at that temperature. Without this information, an accurate calculation cannot be made. However, once that solubility information is available, you could use the definition of percent yield (the mass of the solute divided by the solvent volume multiplied by 100) to calculate the amount of alcohol needed.

Similarly, to calculate how much sulfanilamide will remain dissolved when the mixture is cooled to 0°C, you would need the solubility of sulfanilamide in ethyl alcohol at 0°C. This is because solubility can change dramatically with temperature.

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Calculate the volume of 95% Ethyl Alcohol needed to dissolve 0.1 g sulfanilamide at 78°C (result: 0.476 mL), and then determine how much will remain dissolved when cooled to 0°C (result: 0.006664 g).

A. To calculate this:

Determine the solubility at the given temperature (0.210 g/mL).

Calculate the required volume of solvent:

Volume = mass / solubility = 0.1 g / 0.210 g/mL ≈ 0.476 mL

B. To calculate this:

Determine the solubility at 0°C (0.014 g/mL).

Calculate the amount of sulfanilamide that remains dissolved in 0.476 mL of solvent:

Remaining dissolved = volume x solubility = 0.476 mL x 0.014 g/mL ≈ 0.006664 g

Complete question:

A) Calculate how much 95% Ethyl Alcohol will be required to dissolve 0.1 g sulfanilamide at 78 C. (At 80 C, solubility = 210 mg/mL)

B) Using the volume of solvent calculated in Step 1, calculate how much sulfanilamide will remain dissolved in the mother liquid after the mixture is cooled to ) C. (At 0 C, solubility = 14 mg/mL)

Answer: The mass of fuel when the tank was full is 45.255kg.

Explanation:

To calculate the mass of the fuel, we will use the formula given by the equation:

[tex]\text{Density}=\frac{\text{Mass}}{\text{Volume}}[/tex]

Where,

Density = Density of the gasoline = [tex]42lb\ft^3[/tex]

Volume = Capacity of the fuel tank = [tex]14.8gallons=2.376ft^3[/tex]    (Conversion factor: [tex]1gallon=0.1605ft^3[/tex] )

Mass = Mass of the fuel = ?

Putting values in above equation, we get:

[tex]42lb/ft^3=\frac{\text{Mass}}{2.376ft^3}\\\\\text{mass}=99.792lbs[/tex]

Converting this quantity into kilograms, we use the conversion factor:

[tex]1lbs=0.4535kg\\\\99.792lbs=99.792\times 0.4535=45.255kg[/tex]

Hence, the mass of fuel when the tank was full is 45.255kg.

Answer:  C.  Place the coefficient 2 in front of elemental iron.

Explanation:   The given chemical reaction is

                 3CO(g) + Fe2O3(s) → Fe(s) + 3CO2(g)

As we can see that stiochiometric coefficient of Carbon is balanced and oxygen coefficient is also balanced. The atom left with unbalanced coefficient is Fe.

Thus By Placing the coefficient 2 in front of the elemental iron will lead to the balanced equation.

Thus the balanced equation can be written as -

                 3CO(g) + Fe2O3(s) → 2Fe(s) + 3CO2(g)

The diaphragm can be adjusted during deep breathing exercises, forced breathing, and activities that require stabilizing the abdominal cavity's volume and pressure.

The diaphragm is a key muscle involved in breathing. It separates the thoracic and abdominal cavities and plays a vital role in the expansion and contraction of the thoracic cavity. The diaphragm contracts during inhalation to increase the volume of the thoracic cavity, allowing air to enter the lungs.

Conversely, it relaxes during exhalation to decrease the volume of the thoracic cavity and expel air from the lungs. The conditions under which you would adjust the diaphragm are: During deep breathing exercises, such as diaphragmatic breathing, where you consciously focus on contracting and relaxing the diaphragm to improve lung function.

During forced breathing or hyperpnea, which occurs during activities like exercise or singing, where the diaphragm and other accessory muscles contract to enhance breathing.

During situations where you need to stabilize the volume and pressure of the abdominal cavity, such as in activities like defecation, urination, or childbirth, which involve cooperation between the diaphragm and abdominal muscles.

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The diaphragm is a muscle that contracts and relaxes to allow breathing. It plays a key role in the process of inspiration, where it moves downward to expand the chest and allow air to enter the lungs.

The diaphragm is a dome-shaped, muscular partition separating the thoracic and abdominal cavities in mammals. It plays a crucial role in breathing by contracting and relaxing to change thoracic volume. This action creates pressure variations, facilitating inhalation and exhalation. The diaphragm is essential for respiratory function and overall physiological equilibrium.

The diaphragm is a large, dome-shaped muscle below the lungs that allows breathing to occur when it alternately contracts and relaxes. It plays a crucial role in the process of inspiration, where the diaphragm contracts and moves downward, causing the chest to expand and allowing air to flow into the lungs.

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Final answer:

To react with 9.55 g of Zn(s), you will need 53.1 mL of a 5.50 M HCl(aq) solution.

Explanation:

To determine the volume of 5.50 M HCl(aq) required to react with 9.55 g of Zn(s), we need to use the balanced chemical equation:

Zn(s) + 2 HCl(aq) → ZnCl2 (aq) + H2(g)

From the equation, we can see that 1 mole of Zn reacts with 2 moles of HCl. First, we need to calculate the moles of Zn using its molar mass and mass given:

Moles of Zn = mass / molar mass = 9.55 g / 65.38 g/mol = 0.146 moles

Since the stoichiometric ratio between HCl and Zn is 2:1, the moles of HCl needed will be double:

Moles of HCl = 2 × moles of Zn = 2 × 0.146 mol = 0.292 mol

Finally, to calculate the volume of HCl, we need to use its molarity:

Volume of HCl = moles of HCl / molarity = 0.292 mol / 5.50 M = 0.0531 L = 53.1 mL

Taking look at the dining areas of an eating establishment for the proof of broken light bulbs, flaking paint, and wood damage will minimize the occurrences of physical contamination of food. Physical contamination takes place when the actual objects like hair, glass, dirt, paint, and other physical contaminants contaminate the food.  

Various food safety guidelines had been developed by the Food and Drug Administration to make sure the public safety of food in the restaurants and other public eateries.  

In order to write the Calcium electron configuration we first need to know the number of electrons for the Ca atom (there are 20 electrons). When we write the configuration we'll put all 20 electrons in orbitals around the nucleus of the Calcium atom.

In writing the electron configuration for Calcium the first two electrons will go in the 1s orbital. Since 1s can only hold two electrons the next 2 electrons for Calcium go in the 2s orbital. The next six electrons will go in the 2p orbital. The p orbital can hold up to six electrons. We'll put six in the 2p orbital and then put the next two electrons in the 3s. Since the 3s if now full we'll move to the 3p where we'll place the next six electrons. We now shift to the 4s orbital where we place the remaining two electrons. Therefore the Calcium electron configuration will be 1s22s22p63s23p64s2.

The atomic number of calcium is 20. Then the electronic configuration of calcium is 1 s₂,  2 s₂, 2 p₆, 3 s₂, 3 p₆ 4 s₂ .

The distribution of electrons in an element's atomic orbitals is described by the element's electron configuration. Atomic electron configurations adhere to a standard nomenclature in which all atomic subshells that contain electrons are arranged in a sequence with the number of electrons they each hold expressed in superscript.

One orbital can house a maximum of two electrons, and there are four different types of orbitals (s, p, d, and f). More electrons can be held in the p, d, and f orbitals since they contain various sublevels.

Consequently, the electron configuration of calcium will be 1s22s22p63s23p64s2. The configuration notation gives scientists a simple way to express and record how electrons are organized around an atom's nucleus. As a result, it is simpler to comprehend and forecast how atoms will interact to produce solids.

Thus, the electronic configuration of calcium is 1 s₂,  2 s₂, 2 p₆, 3 s₂, 3 p₆ 4 s₂ .

To learn more about the electronic configuration, follow the link;

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Answer: Option (D) is the correct answer.

Explanation:

When big rocks are broken down into smaller rocks due to the natural processes then this process of breaking is known as mechanical weathering.

Mechanical weathering is also known as physical weathering. It arises due to physical forces caused by rainwater and change in temperature etc.

Thus, we can conclude that out of the given options, physical forces is the cause of mechanical weathering.

The balanced chemical equation for the combustion of benzene is C6H6(g) + 15O2(g) → 6CO2(g) + 3H2O(g). AS is expected to be positive in this process.

The balanced chemical equation for the combustion of benzene, C6H6, is:

C6H6 (g) + 15O2 (g) → 6CO2 (g) + 3H2O (g)

In this process, AS (entropy change) is expected to be positive since the reaction produces more gas molecules (CO2 and H2O) than the reactant (benzene).

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Answer:

Adding more solid.

Explanation:

Hello,

Based on the concern, it is known that an unsaturated solution is made when one adds an amount of the solid that is smaller than its solubility for the given amount of solute at the specified temperature, thus, to make a saturated solution, more solute must be added in order for it to equal the solubility at the very same amount of the solvent and at the same specified temperature.

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Answer:

There are 8.43x10²¹ total atoms in 0.280 g of P₂O₅.

Explanation:

Let's follow some steps to calculate the total atoms.

1st) Calculate the molar mass of P₂O₅

Look for the atomic weight of each atom in the Periodic table:

- Atomic weight of Phosphorus = 31 g/mol

- Atomic weight of Oxygen = 16 g/mol

Then, multiply each atomic weight by its coefficient to calculate the molar mass of P₂O₅:

(Atomic weight of P .2) + (Atomic weight of O .5)= Molar mass of P₂O₅

(31 g/mol.2) + (16 g/mol.5) = 62 g/mol + 80 g/mol = 142 g/mol

2nd) Calculate the moles of P₂O₅ that are contained in 0.280 g

This step is easy using a Rule of three thinking that if 142 g of P₂O₅ represents a mol of P₂O₅ the 0.280 g will be "x" moles:

   142 g -------- 1 mol of P₂O₅

0.280 g -------- x = (0.280 g.1 mol)/142 g =0.002 mol of P₂O₅

This means that 0.002 moles of P₂O₅ weights 0.280g.

3rd) Calculate the moles of P and O

To see clear how many moles of each atoms are in the molecule of P₂O₅ we disassociate it:

                                         P₂O₅   →  2P  +  5O

From the reaction we know that 1 mol of P₂O₅ produces 2 moles of phosphorus and 5 moles of oxygen. Now we can make a relation and thinking that if 1 mol of P₂O₅ produces 2 moles of P the 0.002 moles of P₂O₅ that we have will produce "x" moles of P:

        1 mol of P₂O₅ ----- 2 moles of P

0.002 mol of P₂O₅ ----- x = (0.002 mol.2moles)/1mol = 0.004 moles of P

We use the same reasoning for oxygen:

        1 mol of P₂O₅ ------- 5 moles of O

0.002 mol of P₂O₅ ------- x = (0.002 mol.5moles)/1mol = 0.01 moles of O

Up to here we have 0.004 moles of atoms of phosphorus and 0.01 moles of atoms of oxygen.

4th) Calculate the total atoms

To this step it is important to remember that 1 mol of something representa a quantity of 6.022x10²³ (that is called Avogadro's number) So, 1 mol of atoms represents 6.022x10²³ atoms.

Now, if we know that in 1 mol of phosphorus atoms is equal to 6.022x10²³ atoms of phosphorus the 0.004 moles that we have will be equal to "x" atoms:

        1 mol of P ------ 6.022x10²³ atoms of P

0.004 mol of P ------ x = (0.004 . 6.022x10²³)/ 1 = 2.41x10²¹ atoms of P

Use the same reasoning for oxygen:

     1 mol of O ------ 6.022x10²³ atoms of O

0.01 mol of O ------ x = (0.01 . 6.022x10²³)/ 1 = 6.022x10²¹ atoms of O

Now that we have the number of atoms of phosphorus and oxygen let's sum them to find the total atoms:

2.41x10²¹ atoms of P + 6.022x10²¹ atoms of O = 8.43x10²¹ total atoms

Finally, there are 8.43x10²¹ total atoms (of phosphorus and oxygen) in 0.280 g of P₂O₅.