If you're new to using Chem101's dimensional analysis Drag and Drop questions, or are struggling to input your answer, keep reading for some information on how this question type works, how to fill in the blanks, and some variations on how you can format your answers and equations.
Dimensional Analysis questions look like this:
This question is a basic Dimensional Analysis question that uses the concept of density.
There are three sections of the screen on this problem: The question itself--
Which contains the numbers needed to solve the problem, the units used in the problem, and the final result we are looking for.
The next section has an area for your starting amount and your conversion factors--
along with a series of buttons that allow you to add and remove factors, reset the question, and add an answer.
And, finally, we have a series of blue value tiles and red unit tiles.
In this example, we use 254 mL of liquid as our starting point. The way we do that is by either taking the value and unit directly from the problem by dragging them into the equation with a mouse or finger--
Alternatively, we could use the values and units in the tile bank at the bottom of the screen.
Now that we have determined our starting amount, we start on our first conversion factor. In this problem, we need to convert milliliters to grams. Since we are starting with milliliters, and we have a density of grams per milliliters cubed, we will insert the conversion factor between mL and cm³. The way will do that is by taking 1 mL and 1 cm³. Notice that the units cancel out when they match.
We add an additional factor to convert into grams. We can put in grams and cm³.
Alternatively, we can take the factor and take the g/cm³ tile and it will automatically place the tiles in the numerator and denominator.
We can then finish by adding the 1.24 g and 1 to represent the density.
We can then answer the problem by adding in the final answer.
Following some math, we end up with 315 g. We now need to hit Submit on the upper right corner to lock in this answer and receive our feedback.
And we're complete! If you are having issues with getting questions incorrect or want to start with different values, continue reading, otherwise, you are now ready to work on Dimensional Analysis questions!
Sometimes your first answer won't be correct. Here is a common answer for this question:
Chem101 can analyze the mistake we have made and give us that specific feedback, telling us that instead of having 1.24 g in the denominator, we have to flip it over, which would give us the original correct answer.
And we're set again! If you'd like to learn how to use a different starting value, keep reading.
There isn't one correct starting value for this question and for many-dimensional analysis questions. We started with the 254 mL of liquid previously, but we can also start with 1.24 g/cm³. In this case, we still need to convert to g from mL of the liquid, but we are going to go about this in a different way.
First, we start off with the same conversion factor, converting between mL and cm3. The way we do this is the same – taking 1 cm³ by 1mL. Then we add an additional conversion factor. Now the goal here is to result in grams but if we do our calculation now, we are still in g/mL – we need to get rid of the mL tile!
The way we do that is take 254 mL and put 1 in the denominator. Now our cm3 are crossed out and our mL are crossed out and we are left with just grams. The math leads us to 315 g as our answer. We now submit and there we go!
Hopefully, this gives you a good sense of how you can approach dimensional analysis in Chem101.