Litmus strategy: read the molecule, then plan the reaction

Litmus puts you in an empty dark space with atoms and molecules floating all around you. In the Moleculator you build molecules atom by atom, in the Reactor you react whole compounds in a glass sphere, and in the Carbon Chamber you do the same with carbon. Each one looks like a question of chemistry, and each one is really a question of order: what to make first, and what to keep out of the way while you do.

Count the bonds before you tap anything

Every atom forms a fixed number of bonds. Hydrogen, chlorine, sodium and potassium form one. Oxygen, magnesium and calcium form two. Iron, aluminium and nitrogen form three, and carbon forms four. A molecule is finished when every bond it can make is made, and not before.

So read the goal as arithmetic. Water is an oxygen with two bonds and two hydrogens with one each: three atoms, and the oxygen is the one everything joins. The atom with the most bonds is the centre of its molecule. You start each level holding one atom. If it is a one-bond atom and the centre is out there in the space, tap what you hold to let it go, then tap the centre: it comes to your empty hand, and you build outward from it.

Moleculator: clear the line before you tap

Tap an atom and it glides straight to the one you hold. A free bond grabs the first atom it comes near, all the way along that line, and it does not care what you meant. A hydrogen pulled past the chlorine you were saving for later becomes hydrogen chloride on the way in.

• Turn first. Drag to look round, all the way round and up and down. Before you tap, turn until nothing sits on the line between what you hold and what you want. The atom that would ruin a level is often waiting on the most obvious line.
• Drift closer. Hold a finger down to drift toward what you are looking at, which changes every line in the space.
• Two metals never bond. A sodium can pass right by a magnesium. What a metal has to steer around is the non-metals.
• Build a piece on its own. Some molecules need a part made first: an O–H for aluminium hydroxide, say. Let go of what you hold, build the piece, then bring it to the rest.

Anything you finish that is not a goal turns grey and stays in the space as waste. That is not fatal. What costs you the level is using up an atom a goal needed, because there is always just enough and never a spare.

Reactor: work backwards from the goal

In the Reactor, do not ask what the molecules around you could make. Ask what the goal is made from, then what makes those. Ammonia is nitrogen and hydrogen, so it starts from nitrogen gas and hydrogen gas. Once you know the last reaction, the rest of the level is finding its ingredients, and sometimes making one of them first.

Tap a molecule and it glides into the glass sphere, which holds four. Some reactions go the moment their molecules meet: an acid and a base, a carbonate and an acid, two solutions that make a solid. Others need an agent, one of the four orbs at the bottom.

Pick the agent the reaction really needs

The agents are the ones a school lab or a factory uses, so what you know from chemistry lessons is what works here.

• Iron makes ammonia from nitrogen and hydrogen: the Haber process.
• Vanadium(V) oxide makes sulphur trioxide from sulphur dioxide and oxygen: the Contact process.
• Nickel turns methane and steam into hydrogen and carbon monoxide.
• Manganese(IV) oxide breaks hydrogen peroxide down into water and oxygen.
• Platinum is the catalytic converter: carbon monoxide and nitrogen monoxide become carbon dioxide and nitrogen.
• Heat breaks carbonates down and splits ammonium chloride, and lets hydrogen or magnesium take the oxygen from copper oxide.
• Spark sets hydrogen, methane and carbon monoxide burning in oxygen, and joins nitrogen and oxygen as lightning does.
• Light sets hydrogen and chlorine off, splits silver halides, and swaps a hydrogen on methane for a chlorine.
• Electricity splits water, brine and copper chloride: electrolysis.

A catalyst comes back after the reaction. A spark, light or electricity is used up in the flash.

Two chances, so think before you pick

A wrong agent bounces off the sphere and costs one of your two chances. A wrong agent with no chances left pours the reaction away, and the level is lost. Before you pick, say what the reaction is. If you cannot, look at the goal again.

Keep what you will need

Whatever a goal wants flies up into its orb. Anything else a reaction makes waits above the sphere. Tap it to put it back in, or drag it away to keep it for later. Whatever is still waiting when the next reaction starts is lost, and in a two-step level that can be the ingredient you needed.

The molecules you did not need are real too

Plenty of what floats around you is not part of the answer, and all of it reacts the way it really would. Put a spare base in with your only acid and the acid is gone. Know what will come out before anything goes in.

Carbon Chamber: four agents for carbon

The Carbon Chamber always offers the same four agents, so the question is which one this step needs.

• Nickel adds hydrogen across a double bond: an alkene becomes an alkane.
• Acid is a catalyst. It adds steam across a double bond to make an alcohol, joins an alcohol and an acid into an ester, and splits an ester back with water.
• Heat is heating under reflux: a haloalkane or an ester with an alkali, or an alcohol with hydrobromic acid.
• Oxidiser is acidified potassium dichromate, which turns from orange to green as it works. It turns an alcohol into its acid, and takes methanoic acid all the way to carbon dioxide and water.

Some carbon reactions need no agent at all. Bromine and the hydrogen halides add across a double bond as they meet, and the acids keep all their ordinary chemistry, so vinegar still fizzes with baking soda and still neutralises a base.

The daily molecule

Each day there is one molecule to build, the same for everyone. Build it to keep your streak going. A streak counts days in a row, and only the daily moves it.

When a level goes wrong

Restart is always in the menu at the top left. Every level, and each daily molecule, has been played and won through real taps before it goes out, so there is always a way through.

The short version

• Count the bonds. The atom with the most is the centre.
• Let go and start from the centre if you are holding the wrong atom.
• Turn until the line is clear, then tap.
• In the Reactor, work backwards from the goal.
• Pick the agent a real lab would use. You have two chances.
• Keep a product you will need before the next reaction starts.
• In the Carbon Chamber, ask which of the four agents this step needs.

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