Aluminum (Al) and iron (Fe) each react with hydrochloric...

Name: Aluminum (Al) and iron (Fe) each react with hydrochloric acid solution (HCl) to produce a chloride salt and hydrogen gas, H2(g). A 0.1924 g sample of a mixture of Al and Fe is treated with excess HCl solution. A volume of 159 mL of H2 gas is collected over water at 19.0 °C and 841 Torr. What is the percent (by mass) of Fe in the mixture? The vapor pressure of water at 19.0 °C is 16.5 Torr.
Uploaded: 2020-12-19T19:45:45-08:00
Duration: 3 min 30 s
Channel: David Collins
Description: Aluminum (Al) and iron (Fe) each react with hydrochloric acid solution (HCl) to produce a chloride salt and hydrogen gas, H2(g). A 0.1924 g sample of a mixture of Al and Fe is treated with excess HCl solution. A volume of 159 mL of H2 gas is collected over water at 19.0 °C and 841 Torr. What is the percent (by mass) of Fe in the mixture? The vapor pressure of water at 19.0 °C is 16.5 Torr.

Aluminum (Al) and iron (Fe) each react with hydrochloric acid solution (HCl) to produce a chloride salt and hydrogen gas, H2(g). A 0.1924 g sample of a mixture of Al and Fe is treated with excess HCl solution. A volume of 159 mL of H2 gas is collected over water at 19.0 °C and 841 Torr. What is the percent (by mass) of Fe in the mixture? The vapor pressure of water at 19.0 °C is 16.5 Torr.

Transcript

00:01 These types of questions are common, advanced questions in chemistry stoichiometry.

00:09 The key to answering these questions is to recognize that we have two unknowns, therefore we need two equations.

00:15 We don't know the mass of aluminum and we don't know the mass of iron, but we do know the summed mass is equal to 0 .19 -2 -4 grams.

00:25 So we'll define x as the mass of aluminum and y is the mass of iron.

00:30 Then we need to write the balanced chemical reactions of aluminum with hydrochloric acid and iron with hydrochloric acid.

00:38 We see that there is a two to three -mole relationship between aluminum and hydrogen, and there's a one -to -one relationship between iron and hydrogen gas.

00:49 The next piece of information that was acquired was the pressure, volume, and temperature of the hydrogen gas that was collected over water, because it was collected over water, we need to subtract off the vapor pressure of water first before we use it as our pressure with the ideal gas law to solve for the moles of hydrogen gas.

01:12 Once we do that, then we can convert it into atmospheres by dividing by 760.

01:17 The volume of the hydrogen gas with 159 milliliters, we'll divide that by 1 ,000 to get liters, and then we'll divide the whole thing by rt.

01:26 Temperature was 19 degrees celsius.

01:28 We'll add on 273 .15 to get kelvin.

01:32 Now this is the total moles of hydrogen gas that was produced from an unknown amount of aluminum and an unknown amount of iron.

01:40 But what if we did know those values? if we knew x and y, we should be able to calculate the moles of hydrogen gas that would be produced.

01:50 X is the amount of aluminum.

01:52 If we divide that by the molar mass of aluminum, we'll get moles of aluminum.

01:56 And then if we use the stoichiometric relationship, of 2 to 3, we would get moles of hydrogen gas produced from x amount of aluminum...

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