April 5th

WELCOME BACK EVERYONE! Hope you all had a nice and relaxing spring break!

TODAY WE'RE GOING TO BE DOING PERCENT YIELD AND PERCENT PURITY!

It's the last thing before our test! :D

It's sad, isn't it? :( Okay, let's get on with things!

Percent Yield

 The first thing we'll be covering is percent yield! If you recall from the last day's lab, percent yield is calculated using this formula:

% Yield:

actual mass produced (in grams)           x     100%

theoretical mass produced (in grams) 

Now today we'll be doing problems with this formula.

Question: Zinc reacts with hydrogen chloride to form zinc chloride and and hydrogen gas. If 23.09g of hydrogen chloride was used in this reaction, and 0.44g of hydrogen gas was formed, what is the percent yield?

Use the following steps to solve this question:

1. Write the equation given.

Zn + HCl → H₂ + ZnCl₂
 

2. Balance it!

1Zn + 2HCl → 1H₂ + 1ZnCl₂

3. Now that you have your mole ratio, you need to draw in your mind a mental map of where you are and where you want to go. You want to get from grams of hydrogen chloride to grams of hydrogen gas to find the THEORETICAL yield of hydrogen gas in the equation.

23.09g HCl x 1 mol HCl / 36.5g HCl x 1 mol H₂/ 2 mol HCl x 2g H₂/ 1 mol H

= 0.6326g H₂ with sig figs = 0.63g H₂


Now we'll use the percent yield formula to calculate, well, percent yield!

% Yield:

actual mass produced (in grams)          x 100%

theoretical mass produced (in grams) 

% Yield:

0.44g    x  100%

0.63g

= 69.8%, with sig figs = 70.%

Percent Purity

Percent purity is a lot like percent yield. The formula for percent purity is:

Mass (grams) of pure substance                 x 100%

Mass (grams) of total (impure) substance

Question: If a mass of gold ore weighs 56.2g, and contains 12.2g of pure gold, what is the percent purity?

Simply plug the variables into the formula to determine the purity.

12.2g  x 100%

56.2g

= 21.7% purity

And there you have it! Percent purity and percent yield!

 GOOD LUCK ON THE TEST EVERYONE!


Some brave soul made a percent yield song for his chemistry class:

"♫Percent yield...the most important thing you'll ever learn!"