Final answer:
The molarity of a solution made by dissolving 3.5 g of NaOH in 2.5 dm³ of water is calculated by converting grams to moles using the molar mass, then dividing by the volume in dm³, resulting in a concentration of 0.035 M.
Step-by-step explanation:
To calculate the concentration of a solution in moles per cubic decimeter (mol · dm–3), you must first determine the moles of solute present. For substances like sodium hydroxide (NaOH), this involves using the molar mass to convert from grams to moles. The concentration, or molarity, is then calculated by dividing the moles of solute by the volume of solution in cubic decimeters (dm3).
In the case of dissolving 3.5 g of NaOH into 2.5 dm3 of water, you would calculate the molarity as follows:
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- Find the molar mass of NaOH, which is approximately 40 g/mol.
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- Convert grams of NaOH to moles: 3.5 g × (1 mol / 40 g) = 0.0875 mol
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- Divide moles by volume of solution to find molarity: 0.0875 mol / 2.5 dm3 = 0.035 M
The molarity of the NaOH solution is therefore 0.035 M.