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# Acid and base pH question watch

1. hi can someone explain the example question. I have no clue what XS means ...thanks
2. (Original post by coconut64)
hi can someone explain the example question. I have no clue what XS means ...thanks
• calculated the moles of H+ ions in the acid and the moles of OH- ions in the base
• the number of moles of OH- is greater than the number of moles of H+ by 0.0075 moles, so 0.0075 moles of OH- ions are left in excess (I guess that's what the XS means) after 0.0125 moles of OH- and H+ neutralise each other to form water.
• calculated the concentration of OH- ions in solution using moles and volume
• calculated concentration of H+ - use the fact that [H+]*[OH-]=10^-14
• calculated pH using -log([H+])
3. (Original post by emilysmith268)
• calculated the moles of H+ ions in the acid and the moles of OH- ions in the base
• the number of moles of OH- is greater than the number of moles of H+ by 0.0075 moles, so 0.0075 moles of OH- ions are left in excess (I guess that's what the XS means) after 0.0125 moles of OH- and H+ neutralise each other to form water.
• calculated the concentration of OH- ions in solution using moles and volume
• calculated concentration of H+ - use the fact that [H+]*[OH-]=10^-14
• calculated pH using -log([H+])
Thanks for your detailed explnation, this is making more sense. So the key to solve these questions. Is to find what is in excess ?

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