Conceptual chemistry is easier to understand. Be it moles, reactions or balancing equations, we have seen that most students are capable of getting the concepts with strategic learning. But when it comes to calculations, they take a lot more time, especially when those involve a series of steps.
A student of Methodist Girl’s School, Nicole, who joined our chemistry tuition class under Ms Ong, suffered from the same problem. She could grasp concepts really fast. But when it came to numbers, she froze. However, under the strategic guidance of Ms Ong, she ultimately managed to increase speed through logic and understanding.
Hers was not the only case though. Over the years, our teachers Ms Ong, Mr Lim, Ms Tan and others have noticed this common pattern in students. They can work chemical calculations accurately but not always efficiently.
To get rid of this problem, our esteemed teachers have adopted a four-fold strategy to solve chemical calculations without compromising accuracy.
1. Write the formula down clearly
We ask the students to write the formula for solving the equation first. Let’s explain how it helps calculate faster.
One of our students from Gan Eng Seng School, had a unique talent. He can solve problems in his head and 8 out of 10 times, he reaches the correct answer. But he wastes a lot of time writing down the steps properly afterwards. Mr Lim taught him to write the formulas first , e.g., moles = concentration × volume, before setting to solve the problem in his head.
Within a few months of adopting this habit, his workflow became more organised and his checking time dropped by half.
In Chemistry, writing down the formulas earns you an extra mark, even if the calculation goes wrong sometimes. So even if the habit appears simple, it always costs one point.
2. Convert each unit carefully
In both our regular classes and crash courses in Singapore, we have observed that 80% of the time, calculation failures are a result of unit confusion. That’s why we instruct our students to start calculating AFTER converting.
For example, in one of Miss Lim’s classes, a student forgot to convert 250 mL to 0.250 dm³ while calculating gas volumes. Although she managed to do it in the end, she lost sufficient time and couldn’t finish her mock paper. We took this example to guide all our students to first convert and then calculate. Now, everyone in the same class abides by this rule to speed up their calculations.
3. Follow a proper sequence
We have already mentioned this in one of our previous blogs but it’s essential. So here we are again. For solving chemical problems faster, maintain this sequence:
Formula → Substitution → Simplification → Conclusion
Let’s give you a practical example of how to do it. Consider this question:
A gas occupies 480 cm³ at room conditions. How many moles are present if one mole occupies 24 dm³?
Firstly, write down the formula, which, in this case, is: moles = volume/molar volume
Next, substitute the formula with values from the question:
No. of moles = 0.480 ÷ 24
Thirdly, simplify the equation: No. of moles = 0.020 mol.
Lastly, write the conclusion like – The gas contains 0.020 mol.
Our chemistry tutors call this the ‘4-step anchor’. Even if the student is nervous, this 4-step sequence will help them solve the problem faster than wasting time in mental calculations.
4. Route Mapping For Multi-Step Questions
The first sight of a multi-step chemical calculation may look threatening. But if you can map it properly, your work becomes way easier.
Ready to understand with an example? Here it is.
Question: Calculate the mass of precipitate formed when 500 cm³ of 0.2 mol/dm³ silver nitrate reacts with excess sodium chloride.
The closest route map that we can create for this question will be something like this –
volume → moles of AgNO₃ → molar ratio → moles of AgCl → mass of AgCl.
The sequence will help you solve multi-step problems without getting stuck in the middle. We have noticed an amazing change in our chemistry tuition classes once the students started practicing this sequence drawing. They now solve several steps easily without brooding or getting panicky.
More Tips To Speed Up Chemical Calculations
Besides these four-fold methods, there are some other effective tips to solve chemical calculations faster.
- Use units always – When you’re solving problems in chemistry, it’s mandatory to give the units in every line. Even forgetting once may result in deductions, even if your answer is correct.
- Memorise core formulas – There are many, true. But it always helps to remember the key formulas that appear repeatedly. However, always check if a formula fits the given question.
- Practice ‘sense check’ – If 0.1 mol solution comes out as 250 mol/dm³ concentration, you immediately know something is wrong. To prevent this, you need to have a realistic expectation of the result before you start the calculations.
n our nov and dec crash courses, we can guide you more on this back checking principle. We will give you problems where errors are supposed to happen frequently. When you’ll see firsthand how logical errors happen in the initial steps, you’ll gain a better idea on how to control them. After the course, you’ll see how fast your instinctive power improves while solving chemical problems.
Make The Most Of Our Crash Courses
The holidays are approaching and so are the dates for our primary and secondary crash courses. We assure you that these short bursts of learning sessions aim to relieve you of the burden, not add to it. You’ll get many unique study tips along with structured revisions and strategic tips to improve your problem-solving skills.
Our teachers will make the short lessons fun-filled and entertaining that don’t dull your holiday spirits. Try them once. You’ll feel like enrolling in the next session as well. And that’s our promise!