A solution of 2.0 g of (+)-glyceraldehyde, HOCH2CHOHCHO, in 10.0 ...

Question

A solution of 2.0 g of (+)-glyceraldehyde, HOCH2CHOHCHO, in 10.0 mL of water was placed in a 100-mm cell. Using the sodium D line, a rotation of +1.74° was found at 25 °C.

Determine the specific rotation of 
(+)—glyceraldehyde

Accepted Answer

Hey everyone. Let's solve this problem. It says a solution was prepared by dissolving 1.8 g of minus glycerol to hide in nine mL of water. The solution was placed in a 100 millimeters cell. And the rotation was then measured at 25 degrees Celsius. Using the sodium D. Line. If the rotation observed was negative 1.74 degrees, calculate the specific rotation of minus glycerol to hide. Okay, well there's a formula we can recall and use here which is alpha equals alpha observed over C. Times L. And let's define these variables. So alpha is going to be the specific rotation in degrees the alpha observed. Oops is going to be the observed rotation in degrees and then C. Will be the concentration in grams per milliliters. And L. Is the path length in decimate ear's. Okay, so let's look at what they gave us and see if we could plug these right into our equation. So they gave us a solution prepared by dissolving 1.8 g in nine mL. So we can divide those values to get our concentration in grams per milliliters. Right? So concentration equals 1.8 g in nine mL. That will give us 0.20 g per milliliters. Okay we have our C. Value. I like to line up all the values we're going to use before we start plugging them into the equation. Make sure they're in the correct units as well. So for example the path length we have 100 millimeters. But in our equation we need deciMA eaters. So we need to convert that. So we line up our units millimeters on the bottom. There is 100 in one decima eater. So those units cancel. We divide that, which gives us one decima eater. And then they gave us our rotation observed was negative 1.74° alpha observed. Oops Native 1.74°. Okay, and then we're solving for the specific rotation alpha. Alright, so let's plug these in. So we have alpha. We're looking for Equals negative 1.74 divided by 0.20 g per mil Times one decimate er And that gives us negative 8.7° as our specific rotation. Making see the correct answer choice. That's it for this problem. I hope this video is helpful and thanks for watching.

A solution of 2.0 g of (+)-glyceraldehyde, HOCH2CHOHCHO, in 10.0 mL of water was placed in a 100-mm cell. Using the sodium D line, a rotation of +1.74° was found at 25 °C. Determine the specific rotation of (+)—glyceraldehyde

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