Question

Prelaboratory Assignment: Analysis of an Aluminum-Zinc Alloy

having a difficult time figuring out how to tackle the following:

Name: Date: Section: Prelaboratory Assignment: Analysis of an Aluminum-Zinc Alloy 1. On the following page, construct a graph of N vs % AL. To do this, refer to equation 5 and the discussion preceding it. Calculate for % Al=0.25.50.75, and 100. Place these points on the graph and Draw the best straight line between them. 2. A student obtained the following information from this experiment. Complete the chart: 21 Mass of Capsule Capsule + Alloy 0.1168 g 0.3522 g Temperature Temperature K Barometric Pressure Vapor Pressure of Water (Table 2) Pressure of H, Mass of Alloy Mass of Empty Beaker 751 mm Hg 141.2 g mm Hg 388.3 g Beaker + Water Mass of Water Volume of Water ml Volume H, Volume displaced water Moles H, evolved (equation 6) Liters moles No moles of H, per gram of sample Moles H,JE % Al from graph in problem 1 % Al from equation 5 _

please help! thank you.

equation 5 is included in here

Answer 1

From data :

1. eq (5) N_H2 = ((% Al/100)*0.0556)+(100 - % Al/100)*0.0153))

(N_H2 , is No. of moles of hydrogen produced per g of sample)

• For 0% Al = 0.0153 mole
• For 25% Al = 0.0254 mole
• For 50% Al = 0.0355 mole
• For 75% Al = 0.0455 mole
• For 100% Al = 0.0556 mole

You can construct N_H2 vs % Al graph using these data.

% Al vs Moles of H2 0.06 0.04 Moles of H2 25 50 75 100 % of Al

2.

• Mass of Alloy = 0.3522 g -0.1168 g = 0.2354 g
• mass of water = 388.3 g -141.2 g = 247.1 g
• volume of water = 247.1 g /0.998 g/ml = 247.6 ml (density of water = 0.998 g/ml )
• temperature = 294.15 K
• Vapour pressure of water = 18.7 mm Hg (@ 21 C)
• Now you need data from lab, volume of water displaced you will get Volume of Hydrogen. From volume of Hydrogen you can calculate moles of Hydrogen evolved : 1mol = 22.4 litres (at 273.15 K) Since V1/T1 = V2/T2

Volume of 1 mol at 294.15 K : 22.4 L *294.15 K / 273.15 K = 24.12 L

so, moles of H2 = volume of water displaced / 24.12 L

or Pressure of Hydrogen can be used to calculate moles of H2 : PV = nRT .

From moles of H2 evolved you can calculate % Al by using graph.