Some of the most important lab math to know (in my opinion)

Downloadable version with figures & live links to more resources: bit.ly/importantlabmath
* Metric conversions
* Get really comfortable moving decimal places to convert between μ, m, etc. (esp. μL, mL & L)
* Converting between molecular weight (MW) or formula weight (FW)*, molarity, and weight/volume
* MW (or FW) = g/mol
* Molarity (M) = mol/L
* g/L =(MW)(molarity)
* M = (g/L) / (MW or FW)
* although the terms molecular weight and formula weight are often used interchangeably, molecular weight is technically only for covalent compounds, whereas formula weight can refer to ionic compounds as well as hydrates & other complexes. Both are g/mol
* For protein biochemists, converting between kDa (what the MW for proteins is often given as), mg/mL, & molarity
* 1 kDa = 1000 Da (Daltons)
* 1 Da = 1 g/mol
* 1 kDa = 1000 g/mol
* 1 mg/mL = 1 g/L
* Going from MW in kDa and molarity (M) to mg/mL:
* (MW in kDa)(M x 1000) = mg/mL
* Going from MW in kDa and mg/mL to molarity:
* Molarity = (mg/mL) / ((MW in kDa)(1000))
* Understanding & using when necessary % w/v
* % w/v = g/L x 100%
* 1 % w/v = 1 g / 100 mL
* Making solutions from solids
* If you have a desired volume & concentration:
(Desired volume)(needed mass) = desired concentration
Needed mass = (desired concentration)/(desired volume)
* Calculating the volume of solvent needed to get to a final desired concentration based on a measured amount (e.g. for when you’re measuring small volumes and it’s impractical to weigh out precisely the target mass)
(measured mass)/(needed volume) = desired concentration
Needed volume = (measured mass)/(desired concentration)
* Salvaging solutions by adding extra solvent and/or mass to match what you actually have present in your current solution
* Too much mass? Calculate volume
(Measured mass) / (total volume needed) = desired concentration
Total volume needed = (measured mass) / (desired concentration)
Needed additional volume = total volume needed - current volume
* Too much volume? Calculate mass
(total mass needed) / (current volume) = desired concentration
Total mass needed = (desired concentration)(current volume)
Extra mass needed = total mass needed - current mass
Alternatively, calculate the mass you need to add directly (rather than first finding total then subtracting). To do that…
Extra volume = current volume - intended volume
Extra mass needed = (extra volume)(desired concentration)
If adding that mass will not appreciably change the final volume, just add it. If adding that mass would change the final volume, calculate mass for a higher volume with enough wiggle room. Add the mass for that, then adjust the volume to that higher volume.
* Diluting solutions
* From any form of concentration (as long as same units on both sides)
* C1V1 = C2V2
* Initial concentration (C1) x initial volume (V1) = final concentration (C2) x final volume (V2)
* From relative concentrations (X factors)
* (Desired total volume) / (X factor) = needed volume of the stock solution
* (Volume of the stock solution you want to use)(X factor) = total volume to dilute to
* Making master mixes
* Pre-mix the parts of reaction mixtures that are the same between all reactions. Then add that to the unique parts
* Make more than you need to account for volume loss during transfers
* Serial dilutions
* Dilution factor (DF): how much you are diluting by each time
* e.g. if you’re halving it each time, DF would be 2
* Multiply the initial concentration by (1/DF) raised to the number of dilutions to get the concentration of that dilution
Links to more information
more on metric conversions: blog: bit.ly/metric_calcs ; RUclips: • Metric conversions & s...   
more on sig figs here: bit.ly/significantfiguress & • Figuring out sig figs ...   
more on dimensional analysis: bit.ly/dimensionalanalysising & • Dimensional analysis (...   
more about concentrations: bit.ly/sciencestocksolutions ; RUclips: • Concentration - ways t... & • Working with relative ...    
and a couple cheat sheets for molecular weights: drive.google.com/file/d/1TqCR...    
and concentrations: drive.google.com/file/d/1v7pf...
more lab-mathy things: thebumblingbiochemist.com/let... & • lab math-y stuff  
More on making solutions: blog form: bit.ly/sciencestocksolutions ; RUclips: • Relative concentration... & • Making stock solutions...
More on serial dilutions: bit.ly/serialdilutions
more about all sorts of things: #365DaysOfScience All (with topics listed) 👉 bit.ly/2OllAB0 or search blog: thebumblingbiochemist.com

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