Chemistry IA · Structure 2 · Models of bonding and structure · topic 9 of 25

Why honey flows slowly: glycerol and viscosity · IB Chemistry IA idea: guide, sample graph and step-by-step plan

cheap kit, real chemistry

Honey, syrup, glycerol: hydrogen bonds you can see slowing down a falling ball.

Difficulty●●○ Medium
KitBasic: tall cylinders, steel balls, phone video, thermometer
TimeAbout 10 hours
FitsSL and HL (Stokes' law is physics: introduce it yourself)
  • ✓ you like seeing intermolecular forces at work
  • ✓ you can film with your phone
  • ✓ you enjoy controlling variables

The big idea

← this is your RQ hook!

Glycerol has three –OH groups per molecule, so it forms a dense network of hydrogen bonds with itself and with water. The more glycerol, the harder it is for molecules to slide past each other, so a falling steel ball slows down. For a small ball in a very viscous liquid, the fall time is proportional to the viscosity, so fall time lets you compare viscosities without a viscometer. The catch: viscosity changes a lot with temperature and concentration, so control matters more than clever analysis.

Make it yours: pick one twist

Copying a classic won't show your choices. Pick one of these (or invent your own) and your IA becomes yours.

Swipe for more twists →

Vary temperature instead

Fix one glycerol concentration and change the temperature, roughly 10 to 40 °C, using a water bath.

→ Graph of the natural log of fall time against 1/T linearises an Arrhenius-type relation, giving an energy for flow.
Another liquid

Replace glycerol with propane-1,2-diol or sugar syrup.

→ Compare the number of –OH groups or molecular size. A more chemical discussion.
Change the ball

Use two or three ball diameters.

→ Tests whether relative viscosity is the same whatever ball you use, and shows where the simple law fails.
Analyse the video

Use frame-by-frame video or free tracker software to get speed along the tube.

→ You can check the ball is at steady speed, and the timing uncertainty drops.
A different viscometer

Time a fixed volume draining through a syringe or burette.

→ A second method for the same liquids. The evaluation compares the two.
Give it a purpose

Frame it around honey, syrup or oil: how water content or temperature changes how they flow.

→ A real reason for the introduction. The measured variable stays the same.

Your Chemistry IA research question: run the check

Write your own question first. Then make sure it ticks every box:

  • Names the independent variable (glycerol per cent by mass), its range and how many values, and says what you do about low concentrations.
  • Names the dependent variable (fall time over a fixed distance) and how relative viscosity follows from it.
  • Names the controls (temperature, ball, tube, distance) and how you check the concentration, for example with density.
  • Says how you check the ball has reached steady speed and that the simple fall-time relationship applies.
  • Is narrow enough: around six concentrations, at least three drops each.

Get your RQ checked · S$29

The set-up

One way to set it up. Draw your own version, with your real distances and apparatus, for the Method section.

htiming marks well belowthe top: ball at steady speedT of the liquid, before + aftersame steel ball every run:measure its diameterphone video, side-on,at the same distance

How your Chemistry IA could be laid out

The usual order for a topic like this, what each part needs to show, and roughly how much of your 3,000 words it takes. The words are all yours.

Research question and context~250
Your question; why viscosity matters in food and industry; what you predict about glycerol content and fall time.
Background chemistry~450
Hydrogen bonding in glycerol and water; viscosity; the falling-ball method, steady speed and the conditions for the simple relationship; prediction of your graph.
Variablestable
Independent, dependent and controlled variables, each with how you set, measure or keep it constant, and why it matters.
Method~450
How each mixture is made and checked (mass, density); tube, ball and its measured diameter; the distance and how you time it; temperature control; repeats.
Safety, ethics, environment~70
Glycerol is low hazard but spills are very slippery: wipe at once. Tall cylinders can tip or break: clamp them or use plastic. Take balls out with a magnet. Dispose of dilute solutions as your school directs.
Raw datatable
One clear table: concentration, density check, temperature, each timed fall, with units and timing resolution.
Processing~300
Mean fall time with spread, relative viscosity, uncertainty and a linearised form if you use one. One worked example.
Graphs and analysis~350
Your graph with error bars; whether the shape fits your prediction; the Reynolds-number check on which points you trust.
Conclusion~350
Answer with numbers: how fall time and relative viscosity change with concentration, within your range, compared with published viscosity data (cite it and its temperature).
Evaluation~600, the biggest part!
Weaknesses ranked by effect (temperature, concentration drift, timing, wall effects); improvements linked to each.
Referencesnot counted
Every source for the method, theory and comparison data.

What your Chemistry IA graph could look like

error bars on EVERY point ✓

Made-up data, to show you the form of a strong graph, not the answer. Yours will look different. example only

2030405060708090-2.5-2.0-1.5-1.0-0.50.00.51.01.5Glycerol / % by mass (± 0.5 %)ln( fall time t / s )simple fall-time modelyour drops (mean times), with error barsat low glycerol the ball is fast:is the simple model still valid?ILLUSTRATIVE · MADE-UP DATA
  • Taking ln of the time spreads the data out and linearises a steep rise. Say why you chose it.
  • Error bars on every point. Short times have the biggest relative uncertainty, so these bars are the longest in real data.
  • Say which points you trust. Work out a Reynolds number for each: with a 1 mm steel ball only the strongest mixtures get near the slow-flow limit where time is proportional to viscosity.
  • Both axes carry units, and the uncertainty of what you set.
  • Another graph to consider: ln of relative viscosity against 1/T, if you vary temperature instead.

Which uncertainty matters most?

rank them: don't just list them

Rank by the effect on your result, relative viscosity, not on raw readings. Here is a made-up 70 % glycerol mixture around 20 °C. Work out yours.

Temperature (±1 K)5%Concentration drift (±0.5 %)4.3%Timing (±1 frame of 1.3 s)2.6%Ball diameter (±0.01 mm of 1 mm)2%Fall distance (±1 mm of 200 mm)0.5%biggest effect: discuss this first!% uncertainty in relative viscosity at 70 % glycerolILLUSTRATIVE · MADE-UP NUMBERS

Your game plan

film the trial run to check the timing

Tick steps off as you go. We'll remember on this device.

0 of 11 done

  1. Read and predictRead about hydrogen bonding in glycerol and about viscosity. Predict how fall time changes with glycerol content, and why the change should get steeper at high content.
  2. Trial run (1 lesson)Drop the ball in one mixture, three times. Is the ball falling in the centre? Is it at steady speed by your first mark? Can you time it to a fraction of a second?
  3. Decide range, distance and repeatsChoose around six concentrations and decide what to do at low glycerol if the ball falls too fast to time. Pick the distance and the number of repeats, with reasons.
  4. Make and check the mixturesMake each mixture by mass, mix gently to avoid bubbles, and check the density. Store them closed.
  5. Control temperatureDecide how you hold the liquid at one temperature and how you read it each time.
  6. CollectFilm side-on and time from the video. Record every fall, not just the mean.
  7. ProcessWork out mean time and spread. Decide how to turn time into relative viscosity, and whether a ln or ratio helps.
  8. Graph and interpretPlot with error bars. Which points do you trust? Does the shape match your hydrogen-bonding prediction?
  9. EvaluateRank the weaknesses with numbers. Make each improvement specific.
  10. Write, then cutWrite in the order of the layout above, within 3,000 words. Tables, calculations and graphs are not counted.
  11. Check before your teacher's draftRun the checklist, then get your RQ or draft checked. Your teacher reads one draft only.

Chemistry you'll need

Traps to avoid in this Chemistry IA

  • Temperature drift. Viscosity changes by several per cent per kelvin for strong solutions, so a warm room or hands on the cylinder show up in your data.
  • Glycerol takes water from the air, so the concentration you made is not the one you measure. Check with density.
  • A ball that is too fast at low glycerol: the fall time is a fraction of a second, a stopwatch cannot resolve it, and time is no longer proportional to viscosity.
  • Timing from the top of the tube, before the ball has reached steady speed.
  • A ball near the wall, which slows it. Use a wide tube and drop the ball down the centre.
  • Air bubbles in the liquid or stuck to the ball after mixing. Let the mixture settle first.
  • Changing the ball between concentrations without noting it.

More Chemistry IA ideas like this

Make sure it's yours

This guide shows how a topic like this is usually approached. It is not an IA. Your question, choices, data, analysis and words must be your own: change something, tell your teacher where the idea came from, and follow your school's rules on outside help.

Get your RQ checked · S$29