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# A2 chemistry question watch

1. Solubility data for barium hydroxide and calcium hydroxide are given in the table below.

Compound Solubility at 20 °C / g dm–3
barium hydroxide 38.9
calcium hydroxide 1.73

(i) Use the data given in the table to calculate the concentration, in mol dm–3, of a saturated solution of calcium hydroxide (Mr = 74.1) at 20°C.
................................ ................................ ................................ ...............
................................ ................................ ................................ ...............
(1)
(ii) Suggest one reason why calcium hydroxide solution is not used in the titration of a 0.200 mol dm–3 solution of an acid.

Can anyone explain whats going on?
2. i) Saturated means it's dissolved as much as possible. So it will be at 1.73gdm^-3. 1.73 g of Ca(OH)2 = 0.0233mol. (3sf) . So it will be 0.0233moldm^-3.

ii) A small volume of 0.2moldm^-3 of acid will react with all of the CaOH solution, because the concentration is so much higher than even a saturated CaOH solution. It means it's very hard to get a precise titration
3. (Original post by BobBobson)
i) Saturated means it's dissolved as much as possible. So it will be at 1.73gdm^-3. 1.73 g of Ca(OH)2 = 0.0233mol. (3sf) . So it will be 0.0233moldm^-3.

ii) A small volume of 0.2moldm^-3 of acid will react with all of the CaOH solution, because the concentration is so much higher than even a saturated CaOH solution. It means it's very hard to get a precise titration
Thanks! But I don't understand the logic of the answer. Why does solubility/mr suddenly give me the concentration?
4. Solubility is the maximum possible cocentration. You just need to convert the gdm^-3 concentration to a moldm^-3 concentration

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