3 AmmoniaNH3 has a molar mass of 17gHydrogen chloride gas has a molar mass of 365gBoth gases on contact react to form white fumes of ammonium chloride When a glasscotton wool dipped in ammonia and another glasscotton wool dipped in hydrochloric acid are placed at opposite ends of a glass tube both gases diffuse towards each other A white disk appears near to glasscotton wool dipped in hydrochloric acid This is because hydrogen chloride is heavierdenser than Ammonia and thus its rate of diffusion is lower