Further Analysis An alloy (a metal mixture) containing magnesium and another met

Question

Further Analysis An alloy (a metal mixture) containing magnesium and another metal, that does not react with HCl(a), needs to analyzed. You are asked to estimate the percent magnesium in the alloy Using what you have learned about enthalpy, describe the procedure you would use to determine the percent magnesium in the alloy If the sample were 30% magnesium calculate the heat evolved if a 5 gram sample were analyzed in that manner. Use your value from this experiment for theHnn for Mg in order to obtain a value. a) b)

Explanation / Answer

Part a

1) Weigh the sample and note down the mass of sample

2) Mg will React with HCl and another metal doesn't.

3) dry and Weigh the another metal

4) mass of Mg = mass of alloy - mass of another metal

5) % Mg = mass of Mg*100/mass of alloy

Part b
enthalpy (Hrxn) of reaction of the balanced reaction

Mg(s) + 2 HCl(aq) MgCl2(aq) + H2(g)

Heat evolved = moles of Mg x Hrxn

= (5 g) x (0.30) / (24 g/mol) x (Hrxn kJ/mol)

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