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SOLUTIONS EXPRESSED AS PERCENTS
Study guide and self-test
Solution concentrations in the biotechnology laboratory are often
expressed as percent solutions in one of three ways
% w/v = 1 gram solute
% v/v = 1 mL solute % w/w = 1 gram solute
100 mL solution
100 mL solution
100 g solution
Let’s try a few examples:
1. Calculate how to make 300 mL of a 35% v/v solution of ethanol in
water
2. Calculate how to make 5 L of a 0.2% v/v solution of methanol in
water
3. Calculate how to make 1 kg of a 5% w/w solution of NaCl in water
4. Calculate how to make 250 mL of a 4.3% w/v solution of KCl in water
5. Calculate how to make 1.3 L of a 1.4% w/v solution of MgCl2 in
water
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ANSWERS:
1. Calculate how to make 300 mL of a 35% v/v solution of ethanol in
water
35% =
35 mL ethanol
100 mL solution
___y___
300 mL solution
=
35 mL ethanol
100 mL solution
y = (35 mL ethanol)(300 mL solution) = 105 mL ethanol
100 mL solution
Measure out 105 mL ethanol and bring to a volume (BTV) of 300 mL with
water.
2. Calculate how to make 5 L of a 0.2% v/v solution of methanol in
water
0.2% =
0.2 mL methanol 5 L solution = 5000 mL
100 mL solution
___y___
5000 mL solution
=
0.2 mL methanol
100 mL solution
y = (0.2 mL methanol)(5000 mL solution) = 10 mL methanol
100 mL solution
Measure out 10 mL methanol and bring to a volume (BTV) of 5 L with
water.
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3. Calculate how to make 1 kg of a 5% w/w solution of NaCl in water
5% = 5 g NaCl
1 kg solution = 1000 g solution
100 g solution
___y___
1000 g solution
=
5 g NaCl
100 g solution
y = (5 g NaCl)(1000 g solution) = 50 g NaCl
100 g solution
Measure out 50 g NaCl and add 950 g water.
4. Calculate how to make 250 mL of a 4.3% w/v solution of KCl in
water
4.3% =
4.3 g KCl
100 mL solution
___y___
250 mL solution
=
4.3 g KCl
100 mL solution
y = (4.3 g KCl)(250 mL solution) = 10.75 g KCl
100 mL solution
Measure out 10.75 g KCl and bring to a volume (BTV) of 250 mL with
water.
5. Calculate how to make 1.3 L of a 1.4% w/v solution of MgCl2 in
water
1.4% =
1.4 g MgCl2
1.3 L solution = 1300 mL
100 mL solution
___y___
1300 mL solution
=
1.4 g MgCl2
100 mL solution
y = (1.4 g MgCl2)( 1300 mL solution) = 18.2 g MgCl2
100 mL solution
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Measure out 18.2 g MgCl2 and bring to a volume (BTV) of 1.3 L with
water.