Using Units of Measurement


Jeff Lawrence (Z31)

Concentrated solutions can be expressed in terms of fold-concentrated. If a standard, final concentration is termed 1X (1 fold concentrated), a solution concentrated ten-fold is termed 10X. A 1X solution can be made from a 10X solution be diluting the 10X solution ten-fold. Examples: 
					Amount
Final (1X)				stock
Conc.	 	Stock		Fold	for 1L	How?				
50 mg/ml	50 mg/ml	1000 X	1 mL	(50,000 mg/ml)/(50 mg/ml) = 1000
10 mg/ml	50 mg/ml	5000 X	200 mL	(50,000 mg/ml)/(10 mg/ml = 5000
20 mg/ml	10 mg/ml	500 X	2 mL	
0.2%		40%		200 X	5 mL	(5 mL)*(200X) = (1000 mL)*(1X)
0.4%		40%		100 X	10 mL	(10 mL)*(100X) = (1000 mL)*(1X)
1%		40%		40 X	25 mL	
50 mM		1 M		20 X	50 mL	
20 mM		1 M		50 X	20 mL	
20 mM		0.4 M		20 X	50 mL	0.4 M=400 mM; (400 mM)/(20 mM)=20X
1. Make 20 mL of 5 M NaOH, molecular weight 40 g/mol: 
	1 M = 40 g/L
	1 M = 4g/(100 mL)
	1 M = 0.4g/(10 mL)
	1 M = 0.8g/(20 mL)
	5 M = 4.0 g/(20 mL)

	∴ Add 4 g NaOH to 20 mL water
2. Make 100 mL of a 200X stock for ampicillin, used at a final concentration of 50 mg/ml: 
	1X =  50 mg/ml
	200X = 200*50 mg/ml = 10,000 mg/ml = 10 mg/ml
	(10 mg/ml)*(100 mL) = 1000 mg = 1 g

	∴ Add 1 g ampicillin to 100 mL water
3. How much of this stock do I use to make plates with a concentration of 20 mg/ml ampicillin? 
	(10,000 mg/ml stock)/(20 mg/ml final) = 500X

	∴ Use 1 mL of this stock for every 500 mL plates; or 2 mL per liter.
4. If 200X methionine is 0.9%, what is the final concentration in plates? 
	(0.9%)/200 = .0045%
	OR: 
	0.9% = 0.9g/(100 mL) = 0.009g/ml = 9 mg/ml = 9000 mg/ml

	&there4 conc. is (9000 mg/ml)/200 = 45 mg/ml
5. How much 40% galactose is added to make 500 mL of MacConkey-Galactose? 
	MacConkey plates use 1% final concentration of galactose
	(40%)/(1%) = 40X

	∴ Use 1 mL per 40 mL plates

	(500 mL)/(40 mL) = 12.5

	∴ Use 12.5 mL of 40% galactose to make 500 mL of 1% galactose
Last Update: Thursday June 19 2014
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Eric Kofoid eckofoid at ucdavis.edu