A chemistry teacher has a lesson and first wants to find out the students’ prior knowledge of volume and weight measurements. He begins by explaining that in chemistry labs, students must be able to mix different liquids in exact proportions. He therefore asks if anyone can say how much a litre is. That’s as much as in a carton of milk, says one student. Well, how much liquid is in the package expressed as decilitres, centilitres or millilitres, the teacher asks. It depends on whether the package contains water, milk, yoghurt or syrup, because the liquids have different weights,” another student replies. It doesn’t at all, sighs the teacher. A litre is always a litre no matter what is in the package, but how is he supposed to explain how many ml are in a litre?
How many ml are in a litre?
The teacher brings out a milk carton to show how to count volume and explains. A carton of milk has a square bottom. The sides are 7 centimeters. The floor area is then 49 square centimetres. How high will the liquid level be if the package is to hold exactly one litre, the teacher wonders. The silence in the classroom settles, but the teacher continues. One litre is equal to 1000 cubic centimetres. Kalle, who is good at mental arithmetic, raises his hand and says that the height is 20.4 centimetres. Right, the teacher replies, delighted that his teaching skills have triumphed. He thinks. But, how many ml are in a litre, i.e. the same as in 1000 cubic centimetres?
How many ml is half a litre?
The chemistry teacher finally starts to realise, converting a litre into a cubic centimetre is getting a bit unnecessarily complicated. He therefore explains that milli means one thousandth. A millilitre, or ml for short, is therefore one thousandth of a litre. A one-litre carton of milk therefore contains 1000 millilitres of milk. Now the teacher asks the quick-thinking Donald to tell him how many ml there are in half a litre. Kalle replies quickly that half a litre is equivalent to 500 millilitres. That’s right, but how did you figure it out so quickly, asks the magister. This time, I peeked into a conversion table, which is available on the internet. Can’t we use such tables instead of making a lot of complicated calculations, Kalle asks. The ambitious teacher gives up and lets his students continue to use conversion tables.