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Miscellaneous
Convert grams to number of moles and particles
Reading time: 3minIn chemistry, one may be interested in converting from grams of a substance to the number of moles and particles. In this example, we will create a question that, given the mass of a substance in grams, the student should compute how many moles and molecules it contains, correct to 2 correct decimal places.
Select the question type
First, we need to select which type of question we will use. There are several possible options , and once again, the best one for this example is Short answer because we expect the student to answer with just the result.
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Create random numbers
Before writing the statement, let us write the algorithm of the question. Open WirisQuizzes Studio by clicking 
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The Basic Mode allows us to retrieve a random integer number in a given interval. We just need one random number: the number of grams of ammonia we'll request to convert into moles and particles. We will name this variable g. As we've seen in previous examples, the variables' names are essential. We need to click on the Add variable button to add it.
Now we have one random variable whose value is between 20 and 50, inclusive. That is all we have to do regarding the generation of the random variables.
Tip
If you want to see more details regarding the Basic Mode of defining random variables, you can see its detailed page here.
Write the correct answers
Now, we need to define the correct answer in the corresponding input field, considering that the answer is not a number now, and we are asking two questions: the number of moles and the number of particles. Firstly, we need to write both subquestions in different lines.
As you may see, the evaluate() command will be automatically displayed there to be used if we want our solution to be computed (in this case, just once, so we would need to write it again for the second subquestion). If we directly write the correct answer without the evaluate() command, the result showed to the student as the expected answer will appear without any performed calculus. Both options are valid, but we prefer to display the final fraction when the students answer the question in this example. Conversely, that's what it would be displayed.
Then, we need to select Grade answer boxes separately in the Input options section not to evaluate the entire content as a single value. We have two choices regarding the grading: either the whole question is correct if all the subquestions are correct, or the whole mark is the sum of the distributed grades for each subquestion. Here, for instance, we distribute the grade equally: 50% for the first one and 50% for the second one.
Tip
Note we have selected a Compound answer. This option allows us to ask for multiple solutions in a single question, which is very useful when both subquestions are related. Everything on the left-hand side of the equal sign will be part of the statement, and on the right-hand side, a box will appear so that the students can answer them accordingly.
Preview the question
It is always a good practice to test how they behave using the Test this question section, even with simple questions. We can make sure the whole grade combines each subquestion's grade.
Change the tolerance
Until now, we were using the default tolerance setting: 0.1 per cent error. In this question, we want to count as correct an answer if it is accurate to two right decimal places. Go to the Validation options section and modify the tolerance field, which becomes two decimal places, as in the animation below.
Tip
Are you interested in all the possible tolerance options and how they work? Visit this detailed tolerance page.
Save the question and assign full grade
Click 
so changes are saved, and WirisQuizzes Studio window closes. Next, assign the full grade to the correct answer.
Write the statement
Finally, we have to write the statement of the problem. Recall we have stored the number of grams in a variable named g. Therefore, as for the correct answer, we have to write the name of the variables preceded by the pound symbol #. We will ask the students to convert g grams of ammonia, NH3, to the number of moles and particles.
Preview the question
Save the question by clicking Save changes and continue editing.
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Click Preview.
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A new window will show up with the question shown as the student will see it. Here, we can test the behaviour of the question again.
Note that the question is not entirely accurate if the student's answer does not have two correct decimal places.
