1 normal acid or base (1N)

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Biologists are sometimes confused by the non-standard[1] chemical unit of normality N. N refers in general to salts while it's most commonly used in the context of acid and bases. N can refere to either the cation or the anion in a hydrolysis. In the context of acid and bases it is generally assumed that N refers to the proton or the hydroxide ion.

  • 1 M (mol/l) = 1 N for an acid that releases 1 proton* when dissolved in water, e.g. HCL (*monoprotic)
  • 1 M (mol/l) = 2 N for an acid that releases 2 protons*, e.g. H2SO4 (*diprotic)

For example, some antigen retrieval methods use 2N hydrochloric acid to open up the tissue to allow antibody binding. This could be a nucleotide analogue, as BrdU or dUTP-TMR in cell proliferation of apoptosis assays.

acid/case molecular weight N vs M
HCl -> 1·H+ + Cl- 36.5 g/mol 1N = 1M = 36.5g/L
H2SO4 -> 2·H+ + SO42- 98 g/mol 2N = 1M = 98g/L
NaOH -> Na+ + 1·OH- 40 g/mol 1N = 1M = 40g/L

1N, 2N HCl

1N HCl

  • 8.3 ml fuming HCl (37% v/v = ~12N = ~12M)
  • 91.7 ml H2O

2N HCl, see also [2]

  • 16.5 ml fuming HCl (37% v/v = ~12N = ~12M)
  • 83.5 ml H2O

Molarity (M) also a non-standard unit

For the nitpickers, molarity M is also a non-standard unit[3]. Expressing this explicitly as mol/L or mol/m3 is clearer to readers less versed in current biological customs.

See also