Pre-Laboratory Assignment 1. Read TECH 191, The Gas Burner and Glass 3. A studen
ID: 562136 • Letter: P
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Pre-Laboratory Assignment 1. Read TECH 191, The Gas Burner and Glass 3. A student investigated the stoichiometry of the Working, in this series or another authoritative reaction of zinc (Zn) with HCI solution and reported source for a discussion of glass working. Read TECH the following data. When 0.2158 g of Zn reacted with 325, Volume Measurements, in this series for a dis 10.00 mL of 1.000M HC1, 82.062 g of water was dis- cussion of burets. Read ANAL 350, Standardizing placed. A total of 36.00 ml of 9.501 x 10 M NaOH a Sodium Hydroxide Solution, in this series for a solution was required to titrate the HCI remaining in the reaction mixture at the end of the reaction. The barometric discussion of titration techniques. A student preparing to do this experiment filled room temperature was 27.0 °C and the was 2. the 150-mL beaker with a colorless liquid that supposed to be water. Later, the student feared that pressure was 777 torr. The gram atomic mass of Zn is 65.38 g mol. The density of water at 27.0 °C is 0.9965 g m and its vapor pressure is 27.0 torr. R 1.OMHCI had been used mistakenly instead of water. 8.21 x 102 L-atm K mo1. (Hint: See Calcula- (1) Explain how the student could use a tiny piece of Mg to determine whether the solution in the beaker was 1.0M HCI or would the student observe if the beaker contained HCI solution? If the beaker contained water? tions.) Calculate the volume of the displaced water Note that the volume of the water will (1) water. What, specifically,from its mass. Note that the volume of the water wi be equal to the volume of the gas collected. (2) The student concluded that the beaker con- tained HCI solution, which is toxic and corrosive. Suggest a procedure the student could follow, using reagents available for this experiment, to make the solution safe enough to be poured into the drain, diluting with a large amount of running water (2) Calculate the pressure of the H2 collected (3) Calculate the number ot moles of H2 col- lected, using the ideal gas equation. (3) Describe any safety precautions the student should take in carrying out the procedure mentioned in (2). STOI 369/Stoichiometry of the Reaction of Mg and HCIExplanation / Answer
2. The student has a solution of 1.0 M HCl
(1) To confirm If the solution is HCl or water, the student may take a tiny piece of Mg and drop it in the solution. If evolution of gas (bubbles) is seen from the system then it is confirmed to be HCl and not water.
Mg + 2HCl --> MgCl2 + H2 (g)
Water + Mg has no effect.
(2) The HCl solution must be neutralized first by the addition of a base such as Na2CO3, NaHCO3 or NaOH before it can be poured in the sink. Acid + Base forms salt and water which are non-toxic.
(3) The neutralization of HCl with the base must be carried out in a well ventillated fume hood with the student wearing proper safety gear such as lab coat, safety goggles, hand gloves.
3. Reaction of Zn and HCl
(1) Volume of water displaced = mass of water/density of water
= 82.062 g/0.9965 g/ml = 82.35 ml
(2) Pressure of H2 collected = 777 torr - 27 torr = 750 torr
(3) moles of H2 collected = PV/RT
= (750/760)atm x (82.35/1000)L/(0.0821 L.atm/K.mol)(27oC + 273)K
= 0.0033 mol
(4) initial moles of HCl = 1.0 M x 10ml/1000 = 0.01 mol
(5) moles of HCl remaining at the end = 0.09501 M x 36 ml/1000 = 0.0034 mol
(6) moles HCl reacted = 0.01 - 0.0034 = 0.0066 mol
(7) moles Zn = 0.2158 g/65.38 g/mol = 0.0033 mol
(8) ratio moles(HCl/Zn) = (0.0066/0.0033) = 2
(9) moles(H2 collected/Zn moles) = 0.0033/0.0033 = 1
(10) stoichiometric reaction equation,
Zn (s) + 2HCl (aq) ---> ZnCl2 (aq) + H2 (g)
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