When a college student takes a chemistry class, sometimes they also have to take an ACS Exam created by the American Chemical Society. Students always ask, how is the ACS Exam graded?

The ACS Exam is usually graded based on the National Percentile Rank for that specific exam. Although, this can often depend on your professor. Professors aren’t forced to use the National Percentile Rank to determine a grade. It can be graded on a class curve, or using a combination of methods.

However, chemistry professors will rarely grade the exam using a standard grading scale. (Example: 52/70 = 74% = C) Professors almost never use this method by itself.

Let’s take a closer look at how your professor will likely grade your ACS Exam for chemistry.

The ACS Exam National Percentile Rank

So, the ACS Exam you take will probably say it’s from a different year. This is because it’s been taken by a different group of students before. Data is collected from those student scores to create the percentile rank for that exam.

See the table below (But keep reading to understand it. Percentile does NOT translate to grade):

Table: National Percentile Rank Data from a Real Second Semester General Chemistry ACS Exam

Table: National Percentile Rank Data from a Real Second Semester General Chemistry ACS Exam

ScorePercentile
70100
69100
68100
67100
66100
6599
6499
6399
6298
6198
6098
5997
5896
5796
5695
5594
5493
5391
5290
5188
5087
4985
4883

 

ScorePercentile
4781
4679
4577
4475
4372
4270
4167
4064
3961
3858
3755
3652
3548
3445
3342
3238
3135
3032
2928
2825
2722
2619
2516

 

ScorePercentile
2413
2311
228
217
205
194
183
172
161
151
140
130
120
110
100
90
80
70
60
50
40
30
20

 

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As you can see, the scoring is much different than the standard grading scale. As we mentioned earlier, a 52/70 would be a 74%, or C.

Grading with the National Percentile Rank in this case, a 52/70 would be in the 90th percentile. However, that is just the percentile rank for this specific exam.

Important Note: A Percentile Rank shouldn’t translate to a Grade. For example, the 50th percentile means Average. So, that means the 51th percentile means Above Average.

Does a grade of 51% (F) sound like something Above Average deserves? No..

More on that later.

Grading the ACS Exam on a Curve

Grading on a curve is a standard practice used by many professors to determine students’ grades based on the entire class’s performance.

There are many different methods of grading on a curve. Regardless, the process is similar. Professors examine the raw grades of students, then use those to determine the grade distribution for each student.

Grading the ACS Exam on a curve is a similar concept to the National Percentile Rank method. However, it’s based on just how the class does as a whole.

Keep in mind, some professors that teach multiple classes, might adjust the curve based on the grades for all of their classes combined.

How Your ACS Exam Grade Will Most Likely Be Calculated

There are many professors that come up with their own grading system, while using the National Percentile Rank as a base to do this.

Here’s a real-world example of a professor’s grading system, also considering the National Percentile Rank of the ACS Exam given to students

Using the National Percentile Rank, a score in the 50th percentile is actually considered average. This literally means that this is where most students score. Not that they should get a 50% on the exam.

So, what would “Average” be considered in a standard grading scale?

Some would say 75% would be considered an “Average” score.

That would mean you would first translate, or scale, the 50th National Percentile to score as 75%, then grade or curve from there.

Here’s a common formula:

National Percentile + [ (100-National Percentile) (National Percentile/100) ]

Therefore, if you were in the 50th percentile, the formula would look like this…

Your Grade = 50 + [ (100-50) (50/100) ]

Your Grade = 75 = C

Using the table near the top of this article, let’s look at if you got 45 out of 70 questions correct on the ACS Exam.

In a standard grading system, it would simply look like 45/70 = 64%… D… That looks bad.

However, that’s not the grading system that we just went over. So, let’s look at that.

Using the table at the top, a 45/70 is in the 77th National Percentile Rank.

Let’s using our formula:

Your Grade = 77 + [ (100-77) (77/100) ]

Now watch this…

Your Grade = 94.7%

Huge difference right?

Using a score of 45 out of 70 questions… Standard grading is a grade of 64. Curving the National Percentile Rank is a grade of 94.7

Conclusion: How is the ACS Exam Graded?

Confused yet? Well, you should be. However, you are in a College Chemistry class. So you should be able to understand some of this.

The best thing you can do is ask your professor this exact question. How is the ACS Exam Graded?

If he has trouble telling you, show him or her this article. Tell them it confuses you, or that you understand there’s a lot of different ways to grade the ACS Exam.

The absolute most important thing to remember is that a 50th percentile rank is the average for National Percentile Rank. It doesn’t mean you should get an F and a score of 50%.

The National Percentile Rank is there so that professors can see how the ACS Exam is curved nationally, then use that to scale or adjust their own grading.

On the other hand, I have seen a professor use the standard grading system for the ACS Exam. I’ve only, personally, ever known one professor to do this. He just calculated how many you got correct out of 70. That was your score. I didn’t agree with it. But again, it was up to him how to calculate the score.

I hope this article helped you in some way. Please let me know if you have any questions or suggestions in the comments below!