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CHEM AQA - Amount of Substance - dilution question

Sodium hydroxide is often sold as a concentrated solution containing 12.0 mol dm–3 of sodium hydroxide.
Calculate the volume of water that should be added to 10.0 cm3 of a 12.0 mol dm–3 solution of sodium hydroxide to make a 0.250 mol dm–3 solution. Show your working.

Answer:
Total volume = (10 × 12) / 0.25 = 480 (cm3) M1
Allow any correct method.

Therefore add 470 (cm3) M2
For M2, allow M1 10, even if M1 is incorrect.
Correct answer without working scores 1 mark only.

I don't understand what's going on here...
Original post by Aknwsfg
Sodium hydroxide is often sold as a concentrated solution containing 12.0 mol dm–3 of sodium hydroxide.
Calculate the volume of water that should be added to 10.0 cm3 of a 12.0 mol dm–3 solution of sodium hydroxide to make a 0.250 mol dm–3 solution. Show your working.

Answer:
Total volume = (10 × 12) / 0.25 = 480 (cm3) M1
Allow any correct method.

Therefore add 470 (cm3) M2
For M2, allow M1 10, even if M1 is incorrect.
Correct answer without working scores 1 mark only.

I don't understand what's going on here...



So for dilutions are you familiar with the C1V1=C2V2 equation Concentration x volume ?
Basically the two solutions are proportional, and you can find the unknown V2 (volume of the 0.250 mol dm-3 solution)

If you substitute for V2 the unknown = c1 x v1 /c2
so this is 12 moldm-3 x 10cm3 / 0.250 moldm-3 = 480 cm3 (is the new volume of 0.250mold-3)
The difference between the old solution and new solution is 470cm3
(edited 5 years ago)
Reply 2
Original post by makami11
So for dilutions are you familiar with the C1V1=C2V2 equation Concentration x volume ?
Basically the two solutions are proportional, and you can find the unknown V2 (volume of the 0.250 mol dm-3 solution)

If you substitute for V2 the unknown = c1 x v1 /c2
so this is 12 moldm-3 x 10cm3 / 0.250 moldm-3 = 480 cm3 (is the new volume of 0.250mold-3)
The difference between the old solution and new solution is 470cm3


No, I'm not aware of this. Thank you !
Reply 3
You can’t multiply cm^3 and dm^3, it’s incompatible. So this doesn’t make sense, surely you convert 10 cm3 to dm then work it out?

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