General Chemistry Tutoring

General chemistry is a gateway course. Pre-health, biology, chemistry, and engineering majors all need it, and many need a solid grade to move on. The pace is quick, exams are cumulative, and problems have several steps. A titration question might ask for stoichiometry, then an equilibrium table, then a logarithm. STEM Tutor 360 offers one-on-one general chemistry tutoring built on your own syllabus, homework, and old exams, so you practice at the level your instructor tests.

We cover both semesters. General Chemistry I usually runs from stoichiometry and thermochemistry through quantum theory, bonding, and gases. General Chemistry II picks up intermolecular forces, solutions, kinetics, equilibrium, acids and bases, thermodynamics, and electrochemistry. If your class uses an online homework system, bring the problems you missed, and we will work through the problem types behind them.

A typical general chemistry problem, worked

A buffer contains 0.250 M acetic acid ($\text{p}K_a = 4.74$) and 0.150 M sodium acetate. Find its pH. Then find the pH after 0.0100 mol of $\ce{NaOH}$ is added to 1.00 L of the buffer.

The buffer holds a weak acid and its conjugate base, so use Henderson-Hasselbalch: $$\text{pH} = \text{p}K_a + \log\dfrac{[\ce{A-}]}{[\ce{HA}]} = 4.74 + \log\dfrac{0.150}{0.250} = 4.74 + \log(0.600) = 4.74 - 0.22 = 4.52$$

For the addition, do the stoichiometry first, as if the reaction runs to completion: $\ce{HA + OH- -> A- + H2O}$. In 1.00 L, the acid falls from 0.250 mol to 0.240 mol and the acetate rises from 0.150 mol to 0.160 mol. Then use the buffer equation again: $$\text{pH} = 4.74 + \log\dfrac{0.160}{0.240} = 4.74 - 0.18 = 4.56$$

The pH moved by less than 0.05 units. The same 0.0100 mol of $\ce{NaOH}$ in 1.00 L of pure water would take the pH from 7.00 to 12.00. That difference is what a buffer does.

Where students usually get stuck

• Picking a method before classifying the solution. Strong acid, weak acid, buffer, and salt problems each need a different setup.
• Skipping the stoichiometry step in titration and buffer problems.
• Mixing up $Q$ and $K$, or writing an equilibrium expression that includes solids and pure liquids.
• Using the 5% approximation without checking that it holds.
• Sign and unit slips in thermochemistry, especially J versus kJ.

Looking ahead to organic chemistry and the MCAT

Acid-base reasoning and Lewis structures from General Chemistry II are what Organic I assumes. Students headed to organic chemistry or the MCAT can use sessions to strengthen those skills while the course is still fresh.