BIOTECH - Making Solutions
NAME______KEY_______________Per___
Basic problems
1. You want to make 60 ml of a 20% NaCl solution. (NaCl (table salt) is measured using a balance.)
How much NaCl do you need and how do you make this solution?
0.2 x 60 = 12
Answer 12 g NaCl; (BTV of 60mL)
2. If you put 40.g of sugar into a final volume of 1.0 L of dH2O (distilled), what percent sugar is your
solution?
40 g/ 1000L = 40 g / 1000g = 0.04
Answer 4%
3. You want to make 200. ml of 70.% ethanol and your stock ethanol is 95.%. How much ethanol
and how much dH20 do you need?
(200 mL)(70%) = ?mL (95%)
Answer 147 mL EtOH; (BTV of 200mL)
4. How much 3.0% sodium hypochlorite stock solution (bleach) is needed to make 230 ml of 1.0%
bleach solution? How much dH20 do you need?
(?mL) (3% )= 230mL(1%)
Answer 77 mL EtOH; (BTV of 230 mL)
5. In a hurry to make up some disinfectant, you slosh about 30 ml of dH20 into 250 ml of 70%
ethanol. What is the concentration of this solution?
(250mL + 30mL)(?%) = 250mL(70%)
Answer 62%
6. You need to make 500 ml of buffer solution and your stock solution is 5X. How would you make
this solution? (Remember, solutions are usually 1X when used.)
500mL(1X) = ?(5X)
Answer 100 mL
7. Concentrated lemonade is 4X.
A. How much of this 4X concentrate do you need to make 1L of 1X lemonade?
1L(1X) = ?(4X)
Answer 0.25L = 250 mL
7B. If you like your lemonade sweeter and want 1.5X lemonade, how much concentrate to you need to
make 1L?
1L(1.5X) = ?(4X)
Answer 375 mL
Revised 2/9/2014
Conversions between molarity, percent and mg/ml solutions:
8.
For a-e, note that NaCl is 58.44 g/mol
a) A 1.0 M solution of sodium chloride is __58.44__ mg/ml.
(1mol/L)(58.44g/mol)(1L/103mL)(103mg/1g)
b) What is the molarity of a 1.0 % solution of sodium chloride?
1 percent is 1g/100g
(1g/100g)(100g/0.1L)(1mol/58.44g) = 0.17 M
c) What is the molarity of a 1.0 mg/ml solution of sodium chloride?
(1mg/ml)(1g/103mg)(103ml/1L)(1mol/58.44g) = 0.017 M
d) A 1 mg/ml solution of sodium chloride is ______ %?
since 1 g = 1ml for water, 1mg/ml = 1mg/g = 100mg/100g = 0.1g/100g = 0.1%
e) Rank these solutions from strongest to weakest: 1 M, 1 mg/ml, 1 %
1 Molar has 58.44 g / 1L
1% has 1g/100g = 1g/100ml = 10g/ 1L
1 mg/ml = 0.001g/ml = 1g/1L
More Practice Problems
9. Based on info from the Periodic Table, the molar mass of NaCl is 58.44 g/mol. What steps would
you take to make 50. ml of a 1.0 M sodium chloride solution.
(58.44g/mol)(1mol/L)(0.05L) = 2.92 g; BTV of 50 ml
10. If you purchase 100 µL of a 50 µM solution of DNA, how many micrograms of DNA is this? (This
DNA is 66,000 g/mol.)
(100μL)( 1L/106 μL) (50μmol/L)(1mol/106μmol)(66,000g/mol)( 106μg/1g) = 330 μg
11. You extract RNA from the skin cells of your cat or dog. After purifying it, you measure the RNA
concentration to be 300 ng/µl. If you only need 10 µl of 60 ng/µl concentration, how do you dilute
it?
(300ng/μL)(?) = 10μL(60ng/μL)
? = 2μL of RNA; add 8μL of water
12. Groundwater contains 1.5mM potassium nitrate (101.1 g/mol) and 0.01% magnesium sulfate
(120.4 g/mol). How many grams of each substance is in 125 mL of groundwater?
KNO3: (125mL)(1.5mMol/L)(1mol/103mMol)(101.1g/mol)(1L/103mL) = .0189g = 18.9mg
MgSO: (125mL)(0.01g/100g)(100g/100mL) = .0125g = 12.5mg
13. You want to use 1 µg of DNA in 10 µL of solution. What is the concentration of the DNA solution
you need?
1 µg / 10 µL = 0.1 µg /1 µL = 0.1 mg/mL
Revised 2/9/2014
14. You want to set up a PCR reaction. It must include master mix (containing buffer, enzymes and
nucleotides), a DNA sample, DNA primers and water.
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the final reaction volume is to be 25 µL
Master mix is 2X.
You want 3.0 µg of DNA
Concentration of Stock DNA is 1.0 µg/µL.
You want 1 µL of DNA primers
a. How much of the 2X master mix do you need?
(2X)( ) = (1X)(25 µL)
( ) = 12.5 µL
b. How much of the stock DNA will you use?
1.0 µg/µL = 3.0 µg/?
3 µL = ?
c. How much water should you add?
12.5 µL master mix
3 µL DNA solution
1 µL primers
? µL water
_____________________________
25 µL
?= 8.5 µL
15. You are asked to do a restriction digest on a sample of plasmid DNA. Use the following information to
calculate the volumes of each reagent .
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the final reaction volume is to be 50 µl
Buffer is 5X.
You want 0.5 µg of DNA
Concentration of Stock DNA is 0.70 µg/µl.
Restriction enzyme stock is at a concentration of 10 units/ uL
You want 5 units of restriction enzyme
a. How much of the 5X buffer do you need?
(5X)( ) = (1X)(50 µL)
( ) = 10 µL
b. How much of the stock DNA will you use?
0.7 µg/µL = 0.5 µg/?
0.7 µL = ?
c. How much of the stock restriction enzyme will you use?
10 units/µL = 5 units/?
0.5 µL = ?
d. How much water should you add?
10 µL buffer
0.7 µL DNA solution
0.5 µL enzyme
? µL water
_____________________________
50 µL
?= 38.8 µL
Revised 2/9/2014