CHEM 01LB Lecture Notes - Lecture 3: Exothermic Reaction, Chemical Reaction

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8 Jun 2018
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CHEM 01LB Experiment 3: Composition of an Aluminum-Zinc Alloy
Experimental purpose
The purpose of this experiment is to determine the amount of aluminum present in
an aluminum-zinc alloy
Chemical reaction
The equation for this reaction is outlined as follows:
2Al(s) + 6H+
(aq) → 2Al3+
(aq) + 3H2(aq)
Note: 2 moles of aluminum produce 3 moles of hydrogen gas
Aluminum reacts with a strong acid (HCl)
So 1.00 g Al → 0.0556 mol H2(g)
Zn(s) + 2H+
(aq) → Zn2+
(aq) + H2(g)
Note: 1 mole of zinc produces 1 mole of hydrogen gas
So 1.00 g Zn → 0.0153 mol H2(g)
Calculations
To calculate the number of moles of hydrogen (n) produced:
PhydrogenV = nhydrogenRT
Note: Pbar = Phydrogen + Pwater
Substitution into the Ideal Gas equation:
nhydrogen = RT
(P barP water)V
For a sample containing a
grams of aluminum and z
grams of zinc:
nhydrogen = (a *
0.0556) + (z
* 0.0153)
To calculate the number of moles of hydrogen per gram of sample
:
n*
hydrogen = ( ) (0.0556) + ( ) (0.0153) 100
% Al
100
% Zn
To calculate the percentage of aluminum (% Al) in sample:
n*
hydrogen = ( ) + ( ) ( )
100
% Al 0.0556)( 100
100 − % Al .01530
Additional notes
Hydrogen gas is explosive: no open flames in laboratory
Be sure that no bubbles are present in experimental tubing: this will affect results
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Document Summary

Chem 01lb experiment 3: composition of an aluminum-zinc alloy. The purpose of this experiment is to determine the amount of aluminum present in an aluminum-zinc alloy. The equation for this reaction is outlined as follows: 2al (s) + 6h + (aq) 2al 3+ (aq) + 3h 2(aq) Note : 2 moles of aluminum produce 3 moles of hydrogen gas. Aluminum reacts with a strong acid (hcl) So 1. 00 g al 0. 0556 mol h 2(g) Zn (s) + 2h + (aq) zn 2+ (aq) + h 2(g) Note : 1 mole of zinc produces 1 mole of hydrogen gas. So 1. 00 g zn 0. 0153 mol h 2(g) To calculate the number of moles of hydrogen (n) produced: N hydrogen = (p bar p water)v. For a sample containing a grams of aluminum and z grams of zinc: N hydrogen = ( a * 0. 0556) + ( z * 0. 0153)

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