6 mistakes learners make with chemical reactions, each one named and explained.
A chemical change makes a new substance, which is why the products are worth learning.
The cathode is named where the anode belongs, or a salt is given the wrong family name.
Chemistry pairs its words: anode and cathode, oxidation and reduction, exothermic and endothermic. Each half borrows the other's meaning under pressure.
Question. Which electrode do positive ions move towards during electrolysis?
A common answer. The anode, because positive sounds like it belongs with positive
The answer. The cathode
Why. Opposites attract: positive ions travel to the negative electrode, the cathode. The anode is positive and attracts the negative ions.
Learn the pairs together with what makes them opposite, not as two separate words.
Oxygen or nitrogen is given as the product of a reaction that makes neither.
The named gases are the ones that come to mind, and one of them is usually right somewhere.
Question. Gas from a metal reacting with an acid
A common answer. oxygen
The answer. hydrogen
Why. The acid supplies hydrogen ions, and the metal displaces them.
Match the gas to a reaction you can write out, not to a list of gases.
Evaporation, filtration or condensation is given as the name for displacement.
The separating techniques were learned first and are the vocabulary closest to hand.
Question. A more reactive metal pushing a less reactive one out of its compound
A common answer. evaporation
The answer. displacement
Why. Evaporation makes no new substance; displacement makes two.
Ask whether anything new was made. That splits the two vocabularies cleanly.
Carbon dioxide is chosen as the gas from a metal reacting with an acid.
Carbon dioxide is the gas that comes from the other famous acid reaction, with carbonates.
Question. Gas from a metal reacting with an acid
A common answer. carbon dioxide
The answer. hydrogen
Why. There is no carbon anywhere in the reactants, so no carbon dioxide can form.
Count the elements you started with. A product cannot contain an element that was not there.
Salt alone is given as what iron reacts with to rust.
Salt genuinely does make rusting faster, so it looks like the cause.
Question. What iron reacts with to rust
A common answer. salt only
The answer. oxygen and water
Why. Iron rusts in fresh water too; salt only speeds it up.
Something that speeds a reaction up is not the same as something the reaction needs.
Nitrogen or carbon dioxide alone is given as what iron reacts with.
Both are in the air, and rusting happens in the air.
Question. What iron reacts with to rust
A common answer. nitrogen only
The answer. oxygen and water
Why. Nitrogen is very unreactive, which is why it makes up most of the air unchanged.
Being present in the air is not the same as taking part.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.