Calculations and Gas Laws in Chemistry

These flashcards cover key calculations and concepts related to gas laws and chemical reactions as learned in the laboratory experiment.

How do you calculate the number of moles of magnesium (Mg)?

Divide the mass of magnesium ribbon (in grams) by the molar mass of magnesium (24.3 g/mole).

What equation is used to find the number of moles of hydrogen gas (H₂)?

$$n_{H_2} = \frac{P_{H_2} \times V}{R \times T}$$

How do you determine the pressure of hydrogen gas (H₂)?

$P_{H_2} = P_{bar} - P_{H_2O}$ where P_{bar} is the barometric pressure and P_{H_2O} is the vapor pressure of water.

What is the formula to find the initial moles of hydrochloric acid (HCl)?

$$mol_{HCl (initial)} = M_{HCl} \times L_{HCl}$$

What balanced equation represents the titration reaction between NaOH and HCl?

$$NaOH + HCl \rightarrow NaCl + H_2O$$

How is the moles of HCl that reacted determined?

$$mol_{HCl (reacted)} = mol_{HCl (initial)} - mol_{HCl (excess)}$$

What is the calculation for the moles of hydrogen produced given a volume of 205 mL?

Convert volume to liters: $L = 205 mL \times 10^{-3} L/mL = 0.205 L$.

What is the gas constant R in the ideal gas equation?

$$R = 62.4 L \cdot torr/(mol \cdot K)$$

What impact does a greater than labeled molarity of HCl solution have on calculated moles of HCl reacted?

It would lead to an increase in the calculated moles of HCl reacted.

How does escaping hydrogen gas (H₂) during the reaction affect moles calculated?

It results in a lower calculated amount of produced H₂.

If the pressure of H₂ is taken as the same as barometric pressure, how will it affect calculated moles?

It would lead to an overestimation of the calculated moles of H₂.

How does using a KOH solution instead of NaOH for titration affect calculated moles of HCl?

The calculated moles of HCl reacted would differ based on the reaction stoichiometry.

What units are used for the ideal gas equation gas constant R?

$L \cdot torr/(mol \cdot K)$.

What is vapor pressure of water at 23.0°C?

21.1 torr.

If the flask is not dried prior to weighing, how will it affect calculated molar mass?

The experimental molar mass will be higher than the true molar mass.

What is the percentage of error formula for molar mass calculations?

$\%\,error = \frac{M_{(experimental)} - M_{(true)}}{M_{(true)}} \times 100$.