Question

Show your work, including units, for the following series of calculations: a. How many moles of Al are in 1.25 g of Al? b. For the synthesis of alum you will be performing in lab, what is the molar ratio of Al to alum? In other words, how many moles of alum are produced from 1 mole of Al? c. Starting with 1.25 g of Al, what is the theoretical amount of alum (in g) that can be produced if the reaction goes to completion with 100% yield? d. Calculate the percent yield of alum if a student starts with 1.25 g of Al and produces 14.96 g of alum.

Answer 1

Answer:

1) 1.25 grams of Al is 0.0463 moles of Aluminium

2) Aluminium and alum have a 1:1 ratio that means for 1 mole of aluminium consumed, there is 1 mole of alum produced.

3)The theoretical yield is 21.96 g alum

4)  The percentage yield is 68.97 %

Explanation:

1) Aluminium (Al) has a molar mass of 26.98 g/mole

To calculate the number of moles in 1.25g of Aluminium, we calculate the following equation:

moles aluminium = 1.25g /26.98g/mole = 0.0463 moles

1.25 grams of Al is 0.0463 moles of Aluminium

2) The netto reaction for the synthesis of alum is:

Al3+(aq) + K1+(aq) + 2 SO42-(aq) + 12 H2O ---> KAl(SO4)2.12H2O(s)

Aluminium and alum have a 1:1 ratio that means for 1 mole of aluminium consumed, there is 1 mole of alum produced.

3) Molar mass of aluminium = 26.98 g/mole

moles of aluminium = mass of aluminium / molar mass of aluminium

moles of aluminium = 1.25g / 26.98g/mole = 0.0463 moles

Aluminium and alum have a 1:1 ratio that means for 0.0463 mole of aluminium consumed, there is 0.0463 moles of alum produced.

Mass of alum = moles of alum * molar mass of alum

Mass of alum = 0.0463 moles * 474.22 g/mole = 21.96g alum

The theoretical yield is 21.96 g alum

4) percentage yield = produced mass / theoretical yield

Percentage yield = 14.96g/ 21.96g *100% = 68.97 %

The percentage yield is 68.97 %