This template calculates the molecular mass (or molar mass) of a chemical compound. It is designed to be embedded in infoboxes {{Infobox drug}} and {{Chembox}}, but it can be used in-line just as well.

Use chemical symbols to compose the molecular formula: {{Chem molar mass|H=2|O=1}} (for H
2
O
) → 18.02 g·mol−1

|round= by default the calculated number is rounded to 2 decimals.

|round=no will show all decimals:
{{Chem molar mass|Be=1|round=no}} → 9.0121831 g·mol−1
|round=a number will round to that number of decimals
{{Chem molar mass|Be=1|round=4}} → 9.0122 g·mol−1

|unit= changes the unit for the calculated result. The default unit is g·mol−1.

{{Chem molar mass|H=2|O=1|unit=gram per mole}} → 18.02 gram per mole


The next parameters will always show:
|fixed= to enter a fixed (predefined) value+unit. It will overwrite any calculated value+unit.

|ref=<ref>some source</ref> will add the reference right after the unit.

|comment=Any textis added as a suffix, after a space and unedited (no brackets added etc.).

Example:

{{Chem molar mass|fixed=234.56 g/mol|ref=<ref>Some source</ref>|comment=My Comment}}234.56 g/mol[1] My Comment

|sortable=yes, for use in sortable tables: will add a hidden sortable number, and omits the unit (see table below).

Blank parameter list

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{{Chem molar mass
| round   =
| unit    =
| fixed   =
| ref     =
| comment =
| sortable=
| catname =
}}
{{Chem molar mass
<!-- with 118 chemical symbols: -->|H= |He= |Li= |Be= |B= |C= |N= |O= |F= |Ne= |Na= |Mg= |Al= |Si= |P= |S= |Cl= |Ar= |K= |Ca= |Sc= |Ti= |V= |Cr= |Mn= |Fe= |Co= |Ni= |Cu= |Zn= |Ga= |Ge= |As= |Se= |Br= |Kr= |Rb= |Sr= |Y= |Zr= |Nb= |Mo= |Tc= |Ru= |Rh= |Pd= |Ag= |Cd= |In= |Sn= |Sb= |Te= |I= |Xe= |Cs= |Ba= |La= |Ce= |Pr= |Nd= |Pm= |Sm= |Eu= |Gd= |Tb= |Dy= |Ho= |Er= |Tm= |Yb= |Lu= |Hf= |Ta= |W= |Re= |Os= |Ir= |Pt= |Au= |Hg= |Tl= |Pb= |Bi= |Po= |At= |Rn= |Fr= |Ra= |Ac= |Th= |Pa= |U= |Np= |Pu= |Am= |Cm= |Bk= |Cf= |Es= |Fm= |Md= |No= |Lr= |Rf= |Db= |Sg= |Bh= |Hs= |Mt= |Ds= |Rg= |Cn= |Nh= |Lv= |Mc= |Fl= |Ts= |Og=
| round   =
| unit    =
| fixed   =
| ref     =
| comment =
| sortable=
| catname =
}}

Standard atomic weights used

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Atomic number
Z
Element Molar mass
g/mol
Note
 
0 C
9
H
8
O
4
180.157 fixed value input
0 C
9
H
8
O
4
180.157 g/mol fixed value input
0 C
9
H
8
O
4
180.159 aspirin
1 H 1.008
2 He 4.002602
3 Li 6.94
4 Be 9.0121831
5 B 10.81
6 C 12.011
7 N 14.007
8 O 15.999
9 F 18.998403163
10 Ne 20.1797
11 Na 22.98976928
12 Mg 24.305
13 Al 26.9815385
14 Si 28.085
15 P 30.973761998
16 S 32.06
17 Cl 35.45
18 Ar 39.948
19 K 39.0983
20 Ca 40.078
21 Sc 44.955908
22 Ti 47.867
23 V 50.9415
24 Cr 51.9961
25 Mn 54.938044
26 Fe 55.845
27 Co 58.933194
28 Ni 58.6934
29 Cu 63.546
30 Zn 65.38
31 Ga 69.723
32 Ge 72.63
33 As 74.921595
34 Se 78.971
35 Br 79.904
36 Kr 83.798
37 Rb 85.4678
38 Sr 87.62
39 Y 88.90584
40 Zr 91.224
41 Nb 92.90637
42 Mo 95.95
43 Tc 98
44 Ru 101.07
45 Rh 102.9055
46 Pd 106.42
47 Ag 107.8682
48 Cd 112.414
49 In 114.818
50 Sn 118.71
51 Sb 121.76
52 Te 127.6 (Does not follow atomic number)
53 I 126.90447 (Does not follow atomic number)
54 Xe 131.293
55 Cs 132.90545196
56 Ba 137.327
57 La 138.90547
58 Ce 140.116
59 Pr 140.90766
60 Nd 144.242
61 Pm 145
62 Sm 150.36
63 Eu 151.964
64 Gd 157.25
65 Tb 158.92535
66 Dy 162.5
67 Ho 164.93033
68 Er 167.259
69 Tm 168.93422
70 Yb 173.045
71 Lu 174.9668
72 Hf 178.49
73 Ta 180.94788
74 W 183.84
75 Re 186.207
76 Os 190.23
77 Ir 192.217
78 Pt 195.084
79 Au 196.966569
80 Hg 200.592
81 Tl 204.38
82 Pb 207.2
83 Bi 208.9804
84 Po 209
85 At 210
86 Rn 222
87 Fr 223
88 Ra 226
89 Ac 227
90 Th 232.0377
91 Pa 231.03588
92 U 238.02891
93 Np 237
94 Pu 244
95 Am 243
96 Cm 247
97 Bk 247
98 Cf 251
99 Es 252
100 Fm 257
101 Md 258
102 No 259
103 Lr 266
104 Rf 267
105 Db 268
106 Sg 269
107 Bh 270
108 Hs 269
109 Mt 278
110 Ds 281
111 Rg 281
112 Cn 285
113 Nh 286
114 Fl 289
115 Mc 289
116 Lv 293
117 Ts 294
118 Og 294

Data sources (CIAAW)

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Primarily, the atomic weights used here are defined by CIAAW [1]:

  • "Standard Atomic Weights". Commission on Isotopic Abundances and Atomic Weights (CIAAW). 2015. Retrieved 2015-09-20. (68 elements)
  • CIAAW also published additional lists in spreadsheet format (2013). It has additional conventional values for trade usage, and some background information on the numbers and calculations. (12 elements: B, Br, C, Cl, H, Li, Mg, N, O, S, Si, Tl).
Coplen, T.B.; et al. (2013). "Atomic weights of the elements 2013 (xls)". CIAAW. Retrieved 2015-05-26.
  • Some unstable elements can naturally occur, and so are listed (4 elements: Bi, Th, Pa, U)
  • Additional values are those of the most stable isotopes, as given in List of chemical elements (34 elements). This source is not supported by the CIAAW publications.

See also: "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. February 2016. pp. 265–291. doi:10.1515/pac-2015-0305. eISSN 1365-3075. ISSN 0033-4545. Retrieved 2016-12-29.

Embedding in a template

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The template is designed to be embedded in a template like {{Drugbox}}. The molecular formula can be entered like ...|H=2|O=1, and these values then are passed through to this subtemplate, together with the other parameters like |round=.

For this usage one extra parameter is available:
|catname=. A category name entered here, which will be used as maintenance category for articles that have both calculated and fixed input. These are two inputs for one data value. The maintenance task is to remove the |fixed= input (unless overwriting is intentional).

Know issue: uncertainty

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Atomic weights are given with a precision and uncertainty, for example: 20.1797(6) for neon (more here).

Uncertainty

This template does not maintain the uncertainty (the bracketed part). When done correctly, the uncertainty could influence the result, especially when precision (number of decimals) is larger.

Rounding

This template usually does rounding on the calculated result, to 2 decimals by default:

For neon: {{Chem molar mass|Ne=1}} → 20.18 g·mol−1

Two decimals is common practice for trade and most laboratory situations. However, rounding is set to more decimals, and the compounnd has atoms with less precision, the resulting number will be inaccurate (suggesting a wrong precision). For example strontium :

{{Chem molar mass|Sr=1|round=4}} → 87.6200 g·mol−1

Six elements have values ending with a final decimal being "0" (a zero), like Sn: 118.710. This value does not show for technical reasons (the calculation 'rounds them away'), but it does signify an extra precision. The six elements are Sn, Rh, Ge, Sb, Dy, Bi.

Calculate cumulative uncertainties

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  1. Some source