A sample of gas (1.9 mol) is in a flask at 21 °C and 697 mm Hg. The flask is opened and more gas is added to the flask. The new pressure is 795 mm Hg and the temperature is now 26 °C. There are now __________ mol of gas in the flask.

To find the number of moles of gas in the flask, we can use the Ideal Gas Law equation:

PV = nRT

Where:
P = pressure
V = volume
n = number of moles
R = ideal gas constant
T = temperature

Given:
Pressure before adding gas = 697 mm Hg
Pressure after adding gas = 795 mm Hg
Temperature before adding gas = 21 °C
Temperature after adding gas = 26 °C

We need to convert the temperatures to Kelvin because the Ideal Gas Law equation requires temperature in Kelvin. The relationship between Celsius and Kelvin is given by:

K = °C + 273.15

Converting the temperatures:
Temperature before adding gas = 21 °C + 273.15 = 294.15 K
Temperature after adding gas = 26 °C + 273.15 = 299.15 K

Now, let's find the number of moles of gas using the initial conditions. We'll use the formula:

n1 = (P1 * V) / (R * T1)

Given:
P1 = 697 mm Hg
V = volume (which we don't have, but it cancels out if the volume remains constant)
R = ideal gas constant (0.0821 L*atm/mol*K)
T1 = 294.15 K

Let's calculate n1:

n1 = (697 mm Hg * V) / (0.0821 L*atm/mol*K * 294.15 K)

Now, let's find the number of moles of gas using the new conditions:

n2 = (P2 * V) / (R * T2)

Given:
P2 = 795 mm Hg
T2 = 299.15 K

Let's calculate n2:

n2 = (795 mm Hg * V) / (0.0821 L*atm/mol*K * 299.15 K)

Since the volume remains constant and is the same for both calculations, we can equate n1 and n2:

(697 mm Hg * V) / (0.0821 L*atm/mol*K * 294.15 K) = (795 mm Hg * V) / (0.0821 L*atm/mol*K * 299.15 K)

Now, we can solve for V:

697 mm Hg * 294.15 K = 795 mm Hg * 299.15 K

Now, we have the same volume for both conditions. Therefore, the number of moles of gas remains the same after the additional gas is added. So, the number of moles of gas in the flask is still 1.9 mol.

To find the number of moles of gas in the flask after more gas is added, we can use the ideal gas equation:

PV = nRT

Where:
P = Pressure
V = Volume
n = Number of moles
R = Ideal gas constant
T = Temperature

In this case, we can assume the volume and the moles of the gas remain constant since only more gas is added while the flask is open. Thus, we can set up the following equation:

(P1)(V1) = (n1)(R)(T1)

(P2)(V2) = (n2)(R)(T2)

Where the subscripts 1 and 2 correspond to the initial and final states of the gas respectively.

We can rearrange the equation to solve for n2:

n2 = (P2)(V2) / (R)(T2)

Substituting in the given values:

P2 = 795 mm Hg
V2 = same volume as before the more gas was added
R = 0.0821 L·atm / (mol·K) (the ideal gas constant)
T2 = 26 °C = 26 + 273.15 K (temperature in Kelvin)

n2 = (795 mm Hg)(V2) / (0.0821 L·atm / (mol·K))(26 + 273.15 K)

Simplifying:

n2 = (795 mm Hg)(V2) / (0.0821)(299.15 K)

Now you would need to provide the volume of the flask (V2) in order to continue the calculation.

Use PV = nRT and substitute the SECOND set of numbers to fine the NEW number of mols.