Chemistry Questions

In an assignment, type / and choose Chemical equation, Lewis structure, Particle diagram, Factor-label or Orbital diagram. Each one inserts a question of that kind, named at the top of the block. To change the kind, insert a new question. The same five are in the list when you add a question to a PDF or video assignment. Write the question in Prompt.

The gear, named for the kind (for example Lewis structure settings), holds these settings:

Points (1 by default)

What the question is worth.

Allow student to check answer (Off by default)

Gives students a Check Answer button before they submit. It uses the same grader as the real grade, so the two never disagree.

Partial credit (On by default)

Only for particle diagrams, factor-label and orbital diagrams: credit per particle count, half each for the setup and the result, or per subshell. An equation or a Lewis structure is right or wrong, so its gear has no Partial credit switch.

Under the key, Try an answer as a student would opens the student's own tool for that kind. Answer there and Classla grades it with the real grader against your key as it is now, with the points and the feedback a student would get. Nothing you try is saved.

New blocks take these from your course defaults. Hint shown with a wrong answer (optional) adds your own words to Classla's feedback. Your answer key stays hidden from students until you show correct answers, and then they see it under Correct answer. Chemistry questions also work as live game rounds, graded the moment a student answers, and inside PDF and video assignments.

Students type a formula or an equation in plain notation, and a preview shows it as chemistry while they type. Buttons insert the arrows, the charge caret and the state symbols. Some examples:

• 2H2(g) + O2(g) -> 2H2O(l), a reaction with states.
• SO4^2- and Fe^3+, ions, with the charge after a caret.
• N2 + 3H2 <=> 2NH3, an equilibrium.
• Cu^2+ + 2e^- -> Cu, a half-reaction with electrons.

Under Accepted answers, type your key the same way. Each key shows as chemistry with a check beside it: Balanced, Not balanced with the elements to check, or Can't read with the reason. How to type chemistry lists the notation; students get the same list under their box. Add another accepted answer adds more, up to ten. A key with no arrow makes it a formula question, such as "Write the formula of the sulfate ion."

A student's equation is graded on:

• The species, in any order on each side.
• The coefficients, in lowest whole numbers. Switch on Accept any multiple of the coefficients to also take 4H2 + 2O2 -> 4H2O.
• The charge on every ion, and that charge balances across the arrow.
• How each formula is written. The atoms can come in any order, but a polyatomic ion keeps its parentheses, so Fe2S3O12 is not accepted for Fe2(SO4)3.
• The state symbols, only when Grade state symbols is on. Then (s), (l), (g) and (aq) must match the key.
• The equilibrium arrow. If your key uses <=>, the student must too.

A wrong answer says what is wrong when it can, for example "The equation is not balanced.", "The atoms balance, but the charge does not.", "Balanced, but use the lowest whole-number coefficients." or "The reactants and products are switched."

Students draw the structure on a canvas. They pick an element and click to place an atom, then use the tools: Bond (click two atoms; click a bond to make it double, triple or none), Lone pair, Single e⁻ for an unpaired electron, and Erase. Atoms can be dragged anywhere. Undo and Clear work as you expect, and the keyboard can do everything the mouse can.

Set the key one of two ways:

• Draw it under Answer key with the same tools.
• Open Advanced: fill from a SMILES string, type it and press Fill. For example O=C=O for carbon dioxide or [O-][N+](=O)[O-] for nitrate. Classla adds the lone pairs from each atom's valence electrons. Check the drawing before you save.

Under each key, a line shows what is graded: the valence electrons drawn, how many the formula has (and so the charge, for an ion), and the formal charges, for example "16 valence electrons · CO2 has 16 · formal charges: all 0".

Then choose what students get:

Add resonance structure

For a molecule with resonance, add each structure you accept, up to six. A student who draws any one of them is right.

Elements students can place

The element buttons students see. Left empty, they are the elements in your key. Add others to make students decide.

Students label formal charges

Adds Charge + and Charge − tools, and the charges are graded. A student with the right structure and the wrong charges hears "The structure is right. Check the formal charges."

Start students from the skeleton

The key's atoms are already placed. Students add the bonds and electrons.

Grading compares structures, not pictures. The student needs the same atoms, joined by the same bonds of the same order, with the same lone pairs and unpaired electrons on each atom. Where the atoms sit on the canvas never matters. Feedback points at the problem, for example "Count the valence electrons: the structure should show 16, and yours shows 14." or "Check that every atom has a full valence shell (N does not)."

Students build a picture of the particles in a box. They tap a molecule in the palette to add it, drag particles around, and remove a selected one with the Delete key or the remove button. Clear empties the whole box, and Undo clear puts the particles back until a new one is added. Counts beside the box show how many of each they have placed. The same box, with the same buttons, is how you draw the Before box and the answer key.

In Particles students can place, type a formula such as H2O and press Enter; each one becomes a chip with its molecule drawn. A formula Classla cannot read is refused with the reason. Then draw two boxes with the same palette students use:

Before (optional, shown to students)

These particles appear in a read-only Before box above the student's box, for questions like "Draw the box after the reaction."

Answer key

The particles the student's box should hold. Only the counts are kept.

Answer box label names the student's box, for example "After the reaction". Grading counts each species and ignores where particles sit. With partial credit, each species is an equal share, and a species that should not be there at all costs a share. Feedback names one problem at a time, such as "Check how many H2O particles there are." or "There should be no O2 in the box."

Students set up a dimensional-analysis problem the way they would on paper. The starting quantity is given. They pick conversion factors from a bank to build the chain, flip a factor so the right unit is on top, and watch the units that cancel get struck through. Then they type the result.

Start with

The given quantity on one line: a number, a unit and a substance, such as 25.0 g H2O.

Convert to (unit and substance)

The unit and substance of the answer, such as mol H2O.

Conversion factors students choose from

One line per factor: two equal quantities, such as 1 mol H2O = 18.02 g H2O. A line Classla cannot read says why. Use Add factor for more. Include factors the problem does not need, so students have to choose; they are marked Decoy. Classla works out the answer from your factors and shows it as Answer key, rounded to your significant figures, with the setup it comes from.

Significant figures (Off by default)

The result must have exactly this many significant figures. A right value with the wrong count gets "Right value. Check your significant figures."

Grade the setup only

Students build the chain and type no number.

The setup and the result are each half the points. The setup is right when the units cancel to the target and the factors give the right value; a chain that does not reach the target gets "The units do not cancel to mol H2O. Flip or change a factor." Without a significant figures setting, the result is right within half a percent of the key.

Students fill orbital boxes for an atom or an ion. Each click on a box cycles it through empty, one electron up, a pair, and one electron down. A box never holds more than two electrons, and a pair always has opposite spins, so the Pauli principle is built in.

Atom or ion

Type the species, such as Fe, Fe^3+ or O^2-. Classla computes the key and shows its configuration under the box.

Subshells students fill

Leave it blank for every occupied subshell, or list the ones you want, such as 3d, 4s.

Show noble-gas core

Shows the core, such as [Ar], and leaves only the outer subshells to fill.

The computed key follows the order taught in high school, with the exceptions students learn: chromium and copper (and molybdenum, silver and gold) move an electron from s to d. A positive ion loses electrons from the highest shell first, so Fe^3+ loses its 4s electrons before any 3d. A negative ion gains them in the usual order.

Each subshell is graded on its number of electrons and on Hund's rule. A student who pairs electrons while a box in that subshell is still empty gets "Hund's rule: in 3d, put one electron in each orbital before pairing." With partial credit, each subshell is an equal share.

A calculated value, such as a molar mass or a concentration, goes in a Math answer with a Number part. Two settings there are made for chemistry.

Significant figures (Off by default)

The answer must be written with exactly this many significant figures, and it is compared with your key rounded to that many. A right value with the wrong count gets "Right value. Check your significant figures." Trailing zeros count only after a decimal point, as on the AP exam: 1500 has two, 1500. has four, and 0.0250 has three. Scientific notation such as 6.02 × 10^23 counts the digits before the power.

Units

Besides lengths, masses, times and volumes, the units include mol and mmol, M and mM, K and °C (type degC if you like), J, kJ, cal, kcal and eV, Pa, kPa, atm, bar, torr and mmHg, amu, and Hz. Compound units take parentheses, such as J/(g*°C) or L*atm/(mol*K).

The same unit written another way always matches, so g*°C and g·°C are the same unit. A different unit, such as kJ for a key in J, is wrong ("Check your units.") unless you switch on Accept other units. Then Classla converts it, including 25 °C to 298.15 K.

Anywhere math renders, chemistry does too: in prompts, text blocks, multiple choice options and fill-in-the-blank text. Press the flask button beside the math button in the toolbar, type the chemistry in plain notation, such as H2SO4, Fe^3+ or 2H2 + O2 -> 2H2O, check the preview and press Insert. Select it and press the flask again to edit it. You can also type it between dollar signs with \ce, for example $\ce{SO4^2-}$. Subscripts, charges and arrows come out right, with no need to write them as math.

The assistant can create and edit every kind of chemistry question. Ask it for "a Lewis structure question for ammonia" or "five balancing problems with states graded", and check what it made before you publish. It can also set significant figures and units on a Math answer. The same works from Claude, ChatGPT or Gemini when you connect them to Classla.

When you make your account, or later under What do you teach? in your account settings, pick Science. A science course's student Workspace then shows the graphing calculator, as a math course's does. See The student Workspace. Picking Science also builds you three demo classes, AP Chemistry, Period 3 (Demo), AP Biology, Period 4 (Demo) and AP Physics 1, Period 5 (Demo), each with 24 made-up students and their work turned in. The chemistry class uses all five chemistry blocks, next to answers with units and significant figures, an ICE table and a claim, evidence and reasoning question, and a hidden note above most questions says what that block is good for. To give students a calculator on one assignment, use the assignment's Calculator setting, described on Graphs, proofs and handwork.

• An equation or a Lewis structure is right or wrong; there is no partial credit for either.
• A Lewis structure is graded on its atoms, bonds and electrons, not its shape. Molecular geometry and bond angles are not checked.
• A particle diagram is graded on counts only. Where particles sit, and how they are grouped, is not checked.
• Orbital keys cover the exceptions a high school course teaches: chromium, copper, molybdenum, silver and gold. Any other exception needs a different question type.

• Math Answers and Random Numbers
• Blocks: What an Assignment Is Made Of
• Graphs, Proofs, Handwritten Work and the Calculator
• Modes and Live Games
• The Assistant