Every card in Chemical reactions, Year 9: equations, catalysts and concentration
The whole deck, in order — so you can read it through before your child ever sees it.
← Back to Chemical reactions, Year 9: equations, catalysts and concentration
- Balance this equation for magnesium burning in oxygen: ____Mg + O2 → 2MgO.
2
HintCount the magnesium atoms on the right-hand side, then make the left agree.
WhyThe right-hand side holds two magnesium atoms and two oxygen atoms. O2 already supplies both oxygens, so only the magnesium needs a big number in front to bring the left-hand side up to match.
- Balance this equation for hydrogen burning to make water: ____H2 + O2 → ____H2O.
2; 2
HintStart with the oxygen: O2 brings a pair of atoms, and each water molecule takes only one.
WhyO2 supplies two oxygen atoms and each water molecule holds one, so two water molecules must form. Between them those contain four hydrogen atoms, which takes two molecules of H2.
- How many hydrogen atoms does 2H2O stand for? (number only)
4
HintThe big number multiplies everything in the formula that follows it.
WhyH2O has two hydrogen atoms, and the big 2 in front means two whole molecules, so the count is two lots of two. The same 2H2O holds two oxygen atoms. Counting like this on both sides is how you check that an equation balances.
- To balance H2 + O2 → H2O, a pupil changes the product to H2O2. The atoms now match on both sides. Why is the equation still wrong?
H2O2 is a different substance, not water
HintAsk whether the reaction is still making the same product as before.
WhyA formula is the identity of a substance. H2O2 is hydrogen peroxide, a bleach, so the altered equation describes a reaction that does not happen. To balance, change only how many of each particle there are: the big numbers in front.
- A substance that speeds up a chemical reaction without being used up itself
A catalyst
HintThe exhaust system of a car contains one, to help clean up the fumes.
WhyBecause it is not used up, a small amount can go on working again and again. Different reactions need different ones, so chemists have to find the right one for each job.
- Hydrogen peroxide solution breaks down slowly into water and oxygen. Adding 1 g of manganese dioxide powder makes it fizz rapidly. When the fizzing has stopped, the powder is filtered off, dried and weighed. What is its mass in grams? (number only)
1
HintDecide whether the powder is a reactant or something that only helps the reaction along.
WhyThe powder is a catalyst, so none of it is used up and all of it can be recovered. Weighing it before and after is how you show that a substance acted as a catalyst and not as a reactant.
- A catalyst made by living cells, such as the ones that help to digest your food
An enzyme
HintBiological washing powders contain them to break down stains.
WhyYour body runs thousands of reactions that would be far too slow on their own at body temperature. Each is speeded up by its own enzyme, which is not used up and can work over and over again.
- A reaction gives off 50 cm³ of gas. It is repeated with exactly the same amounts of reactants, plus a catalyst. How much gas is given off this time?
50 cm³, the same as before
HintA catalyst changes how quickly things happen, not how much there is to react.
WhyThe amount of product depends only on how much of the reactants there is to start with. The catalyst lets the reaction finish sooner, but it adds no atoms of its own to the products.
- The catalytic converter in a car exhaust uses the precious metals palladium, rhodium and ____ to speed up reactions that turn harmful gases into less harmful ones.
platinum
HintA silvery metal, costlier than silver, that is also used for expensive rings.
WhyExhaust gases pass over a honeycomb thinly coated with the metal, which gives a huge surface for the reactions to happen on. Because a catalyst is not used up, the same converter can last for years.
- A large jug and a small glass are both filled from the same bottle of ready-mixed squash. Is the squash in the jug more concentrated than the squash in the glass, less concentrated, or the same?
The same
HintConcentration is about how crowded the dissolved particles are, not how many there are altogether.
WhyConcentration compares the amount of dissolved substance with the volume it is dissolved in. The jug holds more squash particles, but it holds more water in exactly the same proportion, so every mouthful tastes alike.
- Water is added to a beaker of salt solution. No salt is added or removed. What happens to the concentration of the solution?
It goes down
HintThe same salt particles now have more liquid to spread through.
WhyAdding water is called diluting. The number of dissolved particles has not changed, but they are spread through a bigger volume, so there are fewer of them in each cubic centimetre.
- When equal volumes of water are used, the solution with more solute dissolved in it is the more ____.
concentrated
HintIts opposite is "dilute".
WhyTwo spoonfuls of sugar in a mug of tea make a stronger solution than one spoonful in the same mug: more sugar particles are packed into the same volume of liquid.
1★ KS3-CHEM-REA-0013
2★ KS3-CHEM-REA-0014
3★ KS3-CHEM-REA-0015
4★ KS3-CHEM-REA-0016
5★ KS3-CHEM-REA-0017
6★ KS3-CHEM-REA-0018
7★ KS3-CHEM-REA-0019
8★ KS3-CHEM-REA-0020
9★ KS3-CHEM-REA-0021
10★ KS3-CHEM-REA-0022
11★ KS3-CHEM-REA-0023
12★ KS3-CHEM-REA-0024
Keep what you learn
Here, nothing is saved. In your child’s own sky every card is scheduled — it comes back just before they’d forget it — and the professor who wrote it is one tap away.