Question

Using the equation: Mg(s) + 2HCl(aq)——> H2(g) + MgCl2(aq) complete the prelab.

Prelab Questions 1. A student following the procedures in this b i collected the following data mass Mg. 0.0243 initial syringe volume, ml 0.8 final syringe volume, ml barometric pressure, torr temperature, 293.5 Calculate the value of the universal gas constant, R. 26.3 748 2. What would be the volume of hydrogen pas produced by the reaction of 0.100 g of magnesium metal, collected at 750 torr and 298 K? Use the value of R found in question 1. 3. The results of this experiment are affected by the care with which each step is completed Describe how each of the following errors would affect the calculated value of R. a. The Mg slid into the HCl in the test tube before the system was sealed off. b. The room temperature increased by 5 °C between the time that the final volume was mea sured and the time that the temperature was recorded. c. The MgO coating was not removed before the Mg sample was placed in the HCI. d. The test tube was filled with 4 mL of 0.10 M HCl instead of 4 mL of 1 M HCI.

Answer 1

1) The moles of H2 produced are calculated:

n H2 = 0.0243 g Mg * (1 mol Mg / 24.3 g) * (1 mol H2 / 1 mol Mg) = 0.001 mol

The constant is calculated:

R = P * V / n * T = (748/760) * (0.0263 - 0.0008) / 0.001 * 293.5 = 0.086 atm * L / mol * H

2) The moles of H2 are calculated:

n H2 = 0.1 / 24.3 = 0.004 mol

The volume is calculated:

V = n * R * T / P = 0.004 * 0.085 * 298 / (750/760) = 0.103 L

3) a) A certain amount of gas produced escapes and the resulting pressure is lower, the calculated constant will be lower.

b) If the temperature rises, the calculated constant will be higher.

c) MgO produces gaseous O2, which is considered as CO2, the calculated R will be higher.

d) The HCl will not be enough to react with all Mg, the constant will be lower.

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