We've recently been developing a number of automatically graded randomized problems. They include random variables for each problem and support feedback for common student errors (for example, an automatic prompt when answers are off by orders of magnitude, suggesting that students check to see if they've converted mL to L for calculations.)
Like all of our efforts, this is a work in progress. If you have any suggestions for problems to add - either Virtual Lab or pen-and-paper problems - please contact us at info@chemcollective.org

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Click on the links below to try one of our automatically graded problems.

Unknown Acid Problem - Perform an experiment to determine the pKa and concentration of an unknown acid.

Limiting Reagents Problem - Perform an experiment to determine the amount of Silver Nitrate in a solution.

Determining Stoichiometric Coefficients - Design and perform an experiment to determine a reaction, including its stoichiometric coefficients.

Thermochemistry Problems

Coffee Problem - Create a solution of coffee with a desired temperature.
Camping Problem - Measure the enthalpy of a reaction