Science & More: Acids, Bases, and Browning Apples

October 27, 2017

The first ever Science & More! Woo-hoo!

 

This week, we explored Acids & Bases and pH levels using apples.

 

We talked for a few minutes about why apples turn brown - I mentioned the term "oxidation" and the kids correctly and quickly connected that with oxygen. So if the enzymes in an apple react with the oxygen in the air, how can we keep them from touching?

 

By coating the apple, of course.

 

We started with several apple slices that had been dunked in various liquids - water, vinegar, lemon juice, and milk - and a control slice not dunked in anything. The apples were labeled 1 through 5, and everyone had to decide which apple slice was which. They then sorted them from least to most brown to see if they could determine which liquid kept the apples looking their best.

 

 We then flipped the number tags over to see if our identifications were correct.

 

 

 

 

 

 

 

 

 

 

 

 

But why did lemon juice work so well to keep an apple from turning that nasty brown color?

(answer: the acidity of the lemon juice neutralizes the enzyme that reacts with oxygen, preventing oxidation or at least delaying it for a while)

 

 

To figure that out, we decided to test the lemon juice, vinegar, milk, and water with pH test strips. We tested juice from a pressed apple as a comparison for the undunked apple. For fun, we also tested dish soap, some of Mr. Mark's Minute Maid Watermelon Juice, and vegetable oil.

 

The results showed that the original dunking liquids were mostly acidic on the pH scale, with lemon juice being the most acidic and the water being neutral. This mostly matched up with how brown they ranked the apple slices at the beginning.

 

 

The kids then had fun testing mixtures of the various liquids with pH strips and seeing how effective the lemon juice was. They had me cut the lemon juice dunked apple slice - which still looked very appetizing - in half to see if the inside would turn brown or if it would stay fresh-looking (answer - the fresh cut turned brown, but the rest of the apple still looked tasty). They also timed how long it took for a freshly-sliced untreated apple to start turning brown (answer - less than 3 minutes for the slices to noticeably change color).

 

Overall, it was lots of fun and the kids enjoyed creating their own experiments at the end!

 

 

 

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