Chemistry
Diluting & mixing
How to make a solution weaker and calculate with concentrations.
What you need first
When juice made from syrup tastes too sweet, you just pour in more water. When the tea is too strong, you make it milder with water. Without calling it chemistry, you dilute solutions all the time. Here you'll learn exactly how it works and how to calculate it.
Diluting lowers the concentration
The tells you how much of a substance is in a certain amount of liquid. Here we measure it in grams per litre, written g/l: 20 g/l means that one litre of solution contains 20 g of the substance dissolved in it. When you dilute, you add water but no new substance. So the amount of substance stays the same, only the liquid increases. That spreads the substance over more water and the concentration drops.
Table salt dissolves up to about 360 g/l, anything more settles at the bottom.
Twice the water, half the concentration
There is a simple relationship here: if you double the amount of liquid without adding substance, the concentration halves. From 30 g in 1 litre (that is 30 g/l), 2 litres give only 15 g/l. If you make three times as much liquid, the concentration is a third as large. You can always calculate it this way: concentration is amount of substance divided by amount of liquid. It works the other way round too: if you know the amount of substance and the concentration, you find the litres by dividing the grams by the g/l. With juice syrup you taste it directly: more water, less sweet.
An important rule to remember
When diluting acids there is a firm rule: water first, then the acid, or something terrible will happen. So you always pour the acid slowly into the water, never the other way round. If you pour water onto concentrated acid, the mixture can suddenly get hot and splash. This is only meant as a thing to remember, not an experiment to copy. At school and at home you never dilute such substances without guidance.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
What happens to the concentration if you add water but no new substance?
1 litre of solution contains 40 g of salt dissolved. What is the concentration in g/l?
You have 30 g of sugar in 1 litre of solution (30 g/l) and top it up with water to 2 litres. What is the concentration now in g/l?
If you double the amount of liquid without adding any substance, then ….
How does the rule for diluting acids go correctly?
There are always 30 g of sugar dissolved. Match each amount of liquid to the right concentration.
Where this leads