Using Concentrations in mol/dm3 Flashcards

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What does a concentration of $1\ \mathrm{mol\ dm^{-3}}$ mean?

1 mole of solute is dissolved in every $1\ \mathrm{dm^3}$ ($1000\ \mathrm{cm^3}$) of solution.

What are the steps to calculate the concentration of a solution in $\mathrm{mol\ dm^{-3}}$ from the mass of solute?

e.g. $4.0\ \mathrm{g}$ of NaOH ($M_r = 40$) dissolved to make $500\ \mathrm{cm^3}$ of solution

1. Moles = mass $\div M_r$ = $4.0 \div 40 = 0.10$ mol
2. Volume in $\mathrm{dm^3}$ = $500 \div 1000 = 0.50$
3. Concentration = moles $\div$ volume = $0.10 \div 0.50 = 0.20\ \mathrm{mol\ dm^{-3}}$

What are the steps to convert a concentration in $\mathrm{g\ dm^{-3}}$ into $\mathrm{mol\ dm^{-3}}$?

e.g. $9.80\ \mathrm{g\ dm^{-3}}$ of KOH ($M_r = 56$)

1. Divide the concentration in $\mathrm{g\ dm^{-3}}$ by the $M_r$
2. $9.80 \div 56 = 0.175\ \mathrm{mol\ dm^{-3}}$

What are the steps to convert a concentration in $\mathrm{mol\ dm^{-3}}$ into $\mathrm{g\ dm^{-3}}$?

e.g. $0.175\ \mathrm{mol\ dm^{-3}}$ KOH ($M_r = 56$)

1. Multiply the concentration in $\mathrm{mol\ dm^{-3}}$ by the $M_r$
2. $0.175 \times 56 = 9.80\ \mathrm{g\ dm^{-3}}$

True or false? To change a volume in $\mathrm{cm^3}$ into $\mathrm{dm^3}$ you multiply by 1000.

False. You divide by 1000 ($1\ \mathrm{dm^3} = 1000\ \mathrm{cm^3}$).