How do you calculate the molar concentration of 20 cm3 HCl and 5 cm3 of water?
Ulex replies You dont say what the concentration was before diluting it with water. Hydrochloric acid is always an aqueous solution the pure substance is hydrogen chloride, a gas. Let us assume that you are given hydrochloric acid of concentration 1 mole per cubic decimetre. If you take 20 cm3 of this and add 5 cm3 of water you will now have 25 cm3 of liquid but the same number of moles. The new concentration is therefore 20/25 ths of what it was before, i.e. 0.8 moles per cubic decimetre. You might find it helpful to remember the rule: New concentration = old concentration x old volume/new volume Risk assessment Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website. For
