Chemistry: Medicine filter semester

Two weeks have passed since the lessons of the filter semester (semestre filtro, the new first semester that decides access to Medicine in Italy) began. Today is 15 September, and the first exam sitting is on 10 December at 11:00: exactly twelve weeks. Those who write to me about Chemistry these days have usually understood one thing and still got another wrong. They have understood that it is not a generic multiple-choice test, it is a university exam worth 6 ECTS credits (CFU) with a precise syllabus. They still misjudge how much time stoichiometry needs compared with everything else — and it is exactly the block that decides the score.

How the exam is structured

Each subject has its own exam: 50 minutes, 31 questions — 21 multiple-choice and 10 completion questions. No logic, no general knowledge, no English. Structure, duration and number of questions are set by Ministerial Decree (DM MUR) no. 941 of 10 July 2026; the dates by Directorial Decree no. 249 of 13 July 2026. The access mechanism comes from Law no. 26 of 14 March 2025 and Legislative Decree 71/2025: free enrolment through Universitaly (the national university enrolment platform) within the limit of places, attendance of three 6-credit courses (Chemistry and biochemical foundations, Physics, Biology), two exam sittings per subject, then a national merit ranking.

The scoring is set by art. 8 of DM 941/2026: +1 for each correct answer, 0 for each omitted one, −0.1 for each wrong one, up to 93 points across the three exams; each exam is marked out of thirty and is passed with at least 18/30. The 21 multiple-choice questions have five options, only one correct (Annex 2). The penalty is small: guessing at random among five options is worth on average $0.2 - 0.8 \times 0.1 = + 0.12$ points, so, unlike the TOLC admission tests with their −0.25, on the multiple-choice questions leaving a blank does not usually pay.

The places for 2026/27 (DM no. 1004 of 6 August 2026) are 30,225 in total — 27,001 Medicine, 1,825 Dentistry, 1,399 Veterinary Medicine — against about 62,200 students enrolled in the filter semester. For Medicine there are about 18,889 places assigned through the national ranking. For the rules on moving to a related degree for those left out, the right reading is the decree and your own university’s website: it is not a procedure I feel comfortable summarising here.

That is all you need to know about the framework. The rest of the post is chemistry.

The syllabus, block by block

1. Atomic structure and the periodic table

Quantum numbers, electron configuration, periodic trends — atomic radius, ionisation energy, electronegativity. Typical questions do not ask you to write out a whole configuration, they ask you to compare two elements: “which of sodium and chlorine has the higher ionisation energy, and why”. Knowing the trend (it grows along a period, it decreases down a group) is worth more than being able to recite the exceptions.

2. Chemical bonding and molecular geometry

Ionic, covalent, metallic; bond polarity; VSEPR geometry; intermolecular forces, in particular the hydrogen bond. The frequent question is “predict the geometry of this molecule” or “which of these substances has the highest boiling point” — which is a question about who forms hydrogen bonds and who does not, not about calculations.

3. Nomenclature and reactions

Oxides, hydroxides, acids, salts, and the balancing of reactions. It is the most mechanical part of the syllabus: you train it by repetition, not by theory. If on 10 December you find yourself working out how to balance a reaction with two or three coefficients, you have already lost the time of two questions.

4. Moles and stoichiometry: the block that decides the grade

Molar mass, limiting reagent, reaction yield, minimum and empirical formula. It is not a unit like the others: it is the foundation on which solutions, gases and electrochemistry rest. Anyone who has not made the calculation of moles automatic arrives at solutions already in difficulty, because there the mole comes back as if it were a given.

5. Solutions

Molarity, percentage concentrations (m/m, m/V), dilution, colligative properties. The most common confusion is between molarity (mol/L of solution) and molality (mol/kg of solvent): they are similar in name and different in the denominator, and in the completion questions swapping them is enough to get wrong a number that looked right.

6. Gases

The ideal gas equation, standard conditions. A compact unit but one that lends itself to quick questions — given P, V, T, find n or the mass — because with a single formula it tests whether you can handle units of measurement cleanly. Worked examples on the gas laws, at university level, are in Leggi dei gas a Chimica generale: esercizi svolti.

7. Thermodynamics and basic kinetics

Enthalpy and spontaneity of reactions, reaction rate and catalysts, chemical equilibrium and Le Châtelier’s principle. Here the questions are more qualitative than numerical: “if I raise the temperature, the equilibrium shifts towards…”, “does a catalyst change the activation energy or the enthalpy of reaction?”. It is worth being able to answer out loud, without calculation.

8. Acids, bases and pH

Strong and weak acids and bases, the constant $K_{a}$ , pH and pOH, salt hydrolysis, a brief look at buffers. Together with stoichiometry it is the block with the most explicit calculations, and one of the worked examples further down is precisely on this. The method with exercises is in Acids, bases and pH: how to calculate pH.

9. Basic electrochemistry

Oxidation numbers, redox reactions, balancing in an acidic medium. Less extensive than the previous ones, but oxidation numbers come in useful outside this block too — they let you recognise a redox reaction among others in general-reaction questions.

10. Biochemical foundations

Functional groups, isomerism, the four classes of biomolecules (carbohydrates, lipids, proteins, nucleic acids). It is the “foundations” part of the course name, not an organic chemistry syllabus: a low level of detail, just enough to recognise a structure and classify it.

The mistakes that cost marks in fifty minutes

Fifty minutes for 31 questions is just over a minute and a half per question: there is no time to redo a calculation from scratch if you get a unit wrong at the start. The mistakes I see repeated:

Units not converted. Millilitres left as they are inside a formula that wants litres, grams instead of moles: it is the most frequent mistake and the most avoidable, the habit of always writing the unit next to the number is enough.
Molarity mistaken for molality. Different denominators (litres of solution against kilograms of solvent), the same mental symbol in the head of someone in a hurry.
Limiting reagent forgotten. You calculate the amount of product from a single reagent without checking whether it is really the one that runs out first — and this is exactly the mistake that exercise (a) below makes impossible to commit by accident, if you follow the procedure.
Wrong sign of the exponent in pH. $pH = - lo g_{10} [H^{+}]$ : forgetting the minus sign or the logarithm turns an acid into a base on paper.
Formulas for dilute solutions applied outside their range. Some approximations (for example in the calculation of the pH of a weak acid) hold only if the concentration is sufficiently greater than $K_{a}$ : using them on a solution that is too dilute gives a result that looks like a number but is not.

Three exercises like the real ones

(a) Stoichiometry with limiting reagent and yield

10.0 g of calcium carbonate ( $CaC O_{3}$ , molar mass 100.09 g/mol) react with 50.0 mL of 2.00 M hydrochloric acid according to:

CaC O_{3} + 2 HCl \to CaC l_{2} + H_{2} O + C O_{2}

How many grams of $C O_{2}$ are formed, knowing that the real yield of the reaction is 85%?

First step, the starting moles:

n_{CaC O_{3}} = \frac{10.0 g}{100.09 g/mol} = 0.0999 mol \approx 0.100 mol

n_{HCl} = 0.0500 L \times 2.00 M = 0.100 mol

The stoichiometry of the reaction wants 2 mol of HCl for each mole of $CaC O_{3}$ : to use up all the carbonate I would need $0.100 \times 2 = 0.200$ mol of HCl, but I have only 0.100. Hydrochloric acid is the limiting reagent.

The moles of $C O_{2}$ produced are calculated from the limiting reagent, not from the other:

n_{C O_{2}} = \frac{n _{HCl}}{2} = \frac{0.100}{2} = 0.0500 mol

Theoretical yield in grams (molar mass of $C O_{2}$ = 44.01 g/mol):

m_{theoretical} = 0.0500 mol \times 44.01 g/mol = 2.20 g

With a yield of 85%:

m_{real} = 2.20 g \times 0.85 = 1.87 g

Anyone who calculates the moles of $C O_{2}$ starting from $CaC O_{3}$ (forgetting the check on the limiting reagent) finds 4.40 g theoretical: double, and it is exactly one of the alternatives that a 31-question test slips in among the others.

If you want to measure how quick you are at calculations like this against the clock, the practice test with the TOLC-MED structure covers chemistry, biology and physics in the same format as the real sitting. The correct answer is free; the guided solution, which explains step by step where you go wrong, unlocks with the first lesson.

(b) pH of a weak acid

Calculate the pH of a 0.10 M solution of acetic acid ( $C H_{3} COOH$ ), knowing that $K_{a} = 1.8 \times 1 0^{- 5}$ .

The dissociation equilibrium is:

C H_{3} COOH ⇌ C H_{3} CO O^{-} + H^{+}

K_{a} = \frac{[ C H _{3} CO O ^{-} ] [ H ^{+} ]}{[ C H _{3} COOH ]} = \frac{x ^{2}}{0.10 - x}

Since $K_{a}$ is much smaller than 0.10, $x$ is negligible compared with 0.10 and we can approximate $0.10 - x \approx 0.10$ :

x^{2} \approx K_{a} \times 0.10 = 1.8 \times 1 0^{- 6} \Rightarrow x \approx 1.34 \times 1 0^{- 3} M

$x$ is the concentration of $H^{+}$ at equilibrium, so:

pH = - lo g_{10} (1.34 \times 1 0^{- 3}) = 2.87

A common mistake here is to use $- lo g_{10} (0.10)$ directly, as if the acid were strong: it would give pH = 1, a value that is too low by almost two units. A weak acid dissociates only in part, and the constant $K_{a}$ is there precisely to tell you how much.

(c) Ideal gases

A 5.00 L container holds a gas at 2.0 atm and 27 °C. How many moles of gas are present?

First compulsory conversion: the temperature must be in kelvin, $27^{\circ} C = 300 K$ . Then the ideal gas equation:

P V = n R T \Rightarrow n = \frac{P V}{R T}

With $R = 0.0821 L \cdot atm \cdot mo l^{- 1} \cdot K^{- 1}$ :

n = \frac{2.0 atm \times 5.00 L}{0.0821 L \cdot atm \cdot mo l ^{- 1} \cdot K ^{- 1} \times 300 K} = \frac{10.0}{24.6} \approx 0.406 mol

The same scheme — isolate the unknown, substitute in consistent units, check the order of magnitude of the result — holds for any variation: pressure at constant volume after heating, volume at constant pressure after cooling. The variable you isolate changes, not the method.

How to organise the twelve weeks

The first criterion is not “how many topics”, it is what depends on what. Moles and stoichiometry come first and right away, not because they are the hardest but because solutions, gases and electrochemistry are all, at bottom, stoichiometry applied with one more variable. Studying them before block 4 is solid means studying it twice without knowing.

Weeks 1–3. Atomic structure, chemical bonding, nomenclature and balancing — the foundations you need to read any reaction without stopping to decipher it.

Weeks 4–6. Moles and stoichiometry, with exercises every day, not now and then. It is the block that is worth the largest investment of time in the syllabus.

Weeks 7–8. Solutions and gases: here stoichiometry comes back, in a different context, and it is the best check that the previous block is really secure.

Weeks 9–10. Acids, bases and pH, basic electrochemistry, thermodynamics and kinetics. They are more compact units but with calculations of their own: two weeks are enough if working with logarithms and exponents is already fluent.

Weeks 11–12. Biochemical foundations (compact, last) and then only timed practice tests, one every two or three days, reviewing your mistakes instead of new topics.

On the second sitting, on 11 January: the strategy changes only if you aim at both with the same weight. If 10 December is the real goal, January should be kept as a safety net, not as a plan B to relax into from November — those who put things off arrive in January with a month less study behind them, not one more.

How we work in lessons

With those preparing for the filter-semester Chemistry I start from where you are weakest: almost always moles and stoichiometry, because it is the block that requires automatic calculation more than theoretical understanding, and it is the one on which a classical or science high school that is “light” on lab work leaves the most gaps. The lessons are mostly commented exercises while the student solves them, not lectures: that is where the systematic mistakes emerge — a skipped unit, a sign in the pH, a limiting reagent not checked.

If you want to place the filter semester in its overall context, I have written a guide on how the filter semester works with dates, structure and ranking, the sister posts of this one on Physics in the filter semester and on Biology in the filter semester, and one on cell and molecular biology. If stoichiometry is your weak point specifically, there is also a dedicated guide to the typical stoichiometry mistakes. The overview of the science subjects, the page on admission tests and the TOLC-MED practice test complete the picture for those who want to train in a structured way.

If you have tried the practice test and your chemistry score did not convince you, or if high school left you with gaps precisely on stoichiometry, write to me and we will talk about it: a first lesson is enough to understand whether the problem is the content, the calculation or the time — they are three different things and are solved in different ways. You will find up-to-date prices and packages on the pricing page — single lesson, 10-hour package — plus a free 30-minute introductory call. Payment offline by bank transfer, Satispay, PayPal, card, Apple Pay or Revolut.

Chemistry in the Medicine filter semester: what to study