Question 1

What is molarity?

Accepted Answer

Molarity (M) is the number of moles of solute per liter of solution, commonly written as mol/L. The formula is: mass (g) = concentration (mol/L) x volume (L) x molecular weight (g/mol). Sub-units include millimolar (mM), micromolar (uM), and nanomolar (nM). Drug research often works in the nM-uM range, while buffer preparation typically uses mM-M concentrations.

Question 2

How do you prepare a molar solution?

Accepted Answer

Calculate the required mass using the molarity formula, weigh the solute on an appropriate balance, dissolve in approximately 80% of the final volume, ensure complete dissolution, then bring to the final volume (QS) using a volumetric flask. The key is to dissolve first, then bring to volume — not add solute to a pre-measured volume of solvent.

Question 3

What is the dilution equation C1V1 = C2V2?

Accepted Answer

The dilution equation C1V1 = C2V2 relates the concentration and volume of a stock solution (C1, V1) to the concentration and volume of the diluted solution (C2, V2). It works because the number of moles of solute remains constant during dilution. C2 must be less than C1, and diluent volume equals V2 minus V1.

Question 4

How do you plan a serial dilution?

Accepted Answer

A serial dilution creates progressively more dilute solutions by repeatedly diluting a portion of the previous solution. Common schemes include 1:10 (10-fold, for log-scale series), 1:2 (2-fold, common in ELISA), and 1:3 (3-fold, balancing resolution and range). Pipetting errors accumulate across steps — a 5% error per step compounds to approximately 26% by tube 6.

Question 5

What concentration units are used in chemistry?

Accepted Answer

The most common units in research chemistry are: Molarity (M) for moles per liter, Percent (w/v, w/w, v/v) where you must always specify the type, Normality (N) which equals equivalents times molarity (used in titration), and parts per million (ppm) meaning mg/L for dilute aqueous solutions (common in environmental testing).

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What is Molarity?

How to Prepare a Molar Solution

The Dilution Equation (C1V1 = C2V2)

Serial Dilution Guide

Common Concentration Units

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