{"id":3595,"date":"2023-10-24T12:08:57","date_gmt":"2023-10-24T10:08:57","guid":{"rendered":"https:\/\/www.em-grade.com\/non-classifiee\/molecular-weight-pm-mw-and-fw\/"},"modified":"2025-05-16T12:26:30","modified_gmt":"2025-05-16T10:26:30","slug":"poids-moleculaire-pm-mw-et-fw","status":"publish","type":"post","link":"https:\/\/www.em-grade.com\/fr\/definitions-de-chimie\/poids-moleculaire-pm-mw-et-fw\/","title":{"rendered":"Poids Mol\u00e9culaire (PM) : Comprendre le Molecular Weight (MW) et le Formula Weight (FW)"},"content":{"rendered":"<p><strong>Qu\u2019est-ce que le poids mol\u00e9culaire (PM) ?<\/strong><\/p>\n<p><strong>Le poids mol\u00e9culaire<\/strong> (PM) d\u00e9signe la masse d\u2019une mole d\u2019une entit\u00e9 chimique (mol\u00e9cule, ion\u2026). En pratique, le PM correspond \u00e0 la<strong> somme des masses atomiques<\/strong> de tous les atomes pr\u00e9sents dans la mol\u00e9cule. <\/p>\n<ul>\n<li><strong>Unit\u00e9 principale<\/strong>\u202f: dalton (Da) ou atomic mass unit (a.m.u)<\/li>\n<li><strong>\u00c9quivalence importante :<\/strong><br \/>\n1 a.m.u = 1 Da = 1 g\u00b7mol\u207b\u00b9<\/li>\n<\/ul>\n<p>\u2697\ufe0f On retrouve syst\u00e9matiquement la valeur du PM indiqu\u00e9e sur les flacons de poudre dans les laboratoires de chimie. <strong>Elle est essentielle pour pr\u00e9parer une solution de concentration pr\u00e9cise<\/strong> (molarit\u00e9).<\/p>\n<hr>\n<h4><strong>Acronymes du poids mol\u00e9culaire : PM, MW et FW<\/strong><\/h4>\n<p>Selon la langue et le contexte, le poids mol\u00e9culaire peut porter diff\u00e9rents acronymes\u202f:<\/p>\n<ul>\n<li><strong>MW\u202f<\/strong>: Molecular Weight (anglais)<\/li>\n<li><strong>FW\u202f<\/strong>: Formula Weight (anglais, pour les compos\u00e9s pr\u00e9sentant une formule brute ou complexes hydrat\u00e9s)<\/li>\n<li><strong>PM<\/strong>: Poids Mol\u00e9culaire (French, rarely used in English)<\/li>\n<\/ul>\n<p><strong>Attention\u202f<\/strong>: FW est parfois utilis\u00e9 pour les sels ou mol\u00e9cules hydrat\u00e9es, o\u00f9 la masse totale inclut celle de mol\u00e9cules d\u2019eau.<\/p>\n<hr>\n<h4><strong>\u00c0 quoi sert le poids mol\u00e9culaire\u202f?<\/strong><\/h4>\n<p>Le poids mol\u00e9culaire est <strong>indispensable <\/strong>pour\u202f: <\/p>\n<ul>\n<li>Convertir une quantit\u00e9 de mati\u00e8re (mole) en masse (grammes)<\/li>\n<li>Pr\u00e9parer des solutions \u00e0 la concentration voulue (calcul de la molarit\u00e9)<\/li>\n<li>Comprendre et anticiper les r\u00e9actions chimiques (rendements, dosages\u2026)<\/li>\n<\/ul>\n<hr>\n<h4><strong>Diff\u00e9rence entre poids mol\u00e9culaire et masse molaire<\/strong><\/h4>\n<p>Les deux notions sont <strong>\u00e9troitement li\u00e9es\u202f:<\/strong> <\/p>\n<ul>\n<li><strong>Poids mol\u00e9culaire <\/strong>= nombre pur (ex\u202f: 98,08 pour H\u2082SO\u2084)<\/li>\n<li><strong>Masse molaire (M) <\/strong>= exprim\u00e9e en g\u00b7mol\u207b\u00b9 (ex\u202f: 98,08\u202fg\u00b7mol\u207b\u00b9)<\/li>\n<li><strong>Utilisation\u202f<\/strong>: En pratique, on utilise souvent l\u2019un pour l\u2019autre, mais la masse molaire pr\u00e9cise bien la relation masse\/quantit\u00e9 de mati\u00e8re.<\/li>\n<\/ul>\n<hr>\n<h4><strong>Comment calculer le poids mol\u00e9culaire\u202f? (vid\u00e9o)<\/p>\n<p> <\/strong><\/h4>\n<p>Pour illustrer le calcul du PM, visionnez cette vid\u00e9o p\u00e9dagogique (en anglais) de TheChemistryNinja\u202f:<\/p>\n<p><iframe loading=\"lazy\" title=\"How to Calculate Molecular Weight from a Chemical Formula\" width=\"1080\" height=\"810\" src=\"https:\/\/www.youtube.com\/embed\/XonYVIQ7atg?feature=oembed&#038;enablejsapi=1&#038;origin=https:\/\/www.em-grade.com\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Qu\u2019est-ce que le poids mol\u00e9culaire (PM) ? Le poids mol\u00e9culaire (PM) d\u00e9signe la masse d\u2019une mole d\u2019une entit\u00e9 chimique (mol\u00e9cule, ion\u2026). En pratique, le PM correspond \u00e0 la somme des&#8230;<\/p>\n","protected":false},"author":8,"featured_media":3506,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_seopress_titles_title":"","_seopress_titles_desc":"","_seopress_robots_index":"","_seopress_robots_follow":"","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"","_seopress_robots_breadcrumbs":"","_seopress_robots_freeze_modified_date":"","_seopress_robots_custom_modified_date":"","_seopress_robots_canonical":"","_seopress_social_fb_title":"","_seopress_social_fb_desc":"","_seopress_social_fb_img":"","_seopress_social_fb_img_attachment_id":0,"_seopress_social_fb_img_width":0,"_seopress_social_fb_img_height":0,"_seopress_social_twitter_title":"","_seopress_social_twitter_desc":"","_seopress_social_twitter_img":"","_seopress_social_twitter_img_attachment_id":0,"_seopress_social_twitter_img_width":0,"_seopress_social_twitter_img_height":0,"_seopress_redirections_value":"","_seopress_redirections_enabled":"","_seopress_redirections_enabled_regex":"","_seopress_redirections_logged_status":"","_seopress_redirections_param":"","_seopress_redirections_type":0,"_seopress_analysis_target_kw":"","_seopress_news_disabled":"","_seopress_video_disabled":"","_seopress_video":[],"_seopress_pro_schemas_manual":[],"_seopress_pro_rich_snippets_disable_all":"","_seopress_pro_rich_snippets_disable":[],"_seopress_pro_schemas":[],"itsec_x_frame_options":"","footnotes":""},"categories":[288],"tags":[230],"class_list":["post-3595","post","type-post","status-publish","format-standard","has-post-thumbnail","category-definitions-de-chimie","tag-fw-pm-fr"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/posts\/3595","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/comments?post=3595"}],"version-history":[{"count":4,"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/posts\/3595\/revisions"}],"predecessor-version":[{"id":11097,"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/posts\/3595\/revisions\/11097"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/media\/3506"}],"wp:attachment":[{"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/media?parent=3595"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/categories?post=3595"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.em-grade.com\/fr\/wp-json\/wp\/v2\/tags?post=3595"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}