Gas laws chemistry

Question

A materials scientist has created an alloy containing aluminum, copper, and zinc, and wants to determine the percent composition of the alloy. The scientist takes a 12.315 g sample of the alloy and reacts with concentrated HCl. The reaction converts all of the aluminum and zinc in the alloy to aluminum chloride and zinc chloride in addition to producing hydrogen gas. The copper does not react with the HCl. Upon completion of the reaction, a total of 10.7 L of hydrogen gas was collected at a pressure of 98.8 kPa and a temperature of 27 degrees celsius. Additionally, 2.154 g of unreacted copper is recovered.

Calculate the mass of hydrogen gas formed from the reaction.

Calculate the mass of aluminum in the alloy sample.

What is the mass percent composition of the alloy?

Answer 1

Hi Dumebi O.,

Looks like your lab walks you through the steps you need to take, in order!

1) First convert that amount of H2 gas to STP or otherwise convert to moles.

2) Subtract the recovered copper from the initial mass to determine the amount of Al + Zn that reacted to make hydrogen gas.

3) Write the respective reactions for dissolution of eacn of Al and Zn. Use those to express the moles amount of H2 generated per unit mass for each of these individual metals

4) the desired information on amounts of each of Al and Zn in the alloy is solved from the linear combination of these reactions. Use a variable (x) to denote the proportion (by mass) of, say, Al. Then (1-x) (for the mass of the two combined, that you obtained in step (2) above) for the mass of the Zn. Solve this on through to find x and (1-x). Done.

-- Cheers, -- Mr. d.