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# Acid/base, ph calculations help watch

1. Need help with this question.

Calculate the pH change to 100cm^3 of 0.200 moldm^-3 HCl solution in a flask if 50 cm^3 of 0.100 mol dm^-3 NaOH is added.

Not entirely sure how to do this question.

The normal way I would workout this question if it didn't mention pH change is:

mol H+ = (100)/(1000) *0.2 = 0.02

mol OH- = 50/1000 * 0.1= 0.005

Xs Mol H+ = 0.02- 0.005 = 0.015

Mol H+ = 0.015/ (150/1000) =0.1

pH= -log (0.1) = 1.

Not sure of what the change is though???
2. (Original post by Super199)
Need help with this question.

Calculate the pH change to 100cm^3 of 0.200 moldm^-3 HCl solution in a flask if 50 cm^3 of 0.100 mol dm^-3 NaOH is added.

Not entirely sure how to do this question.

The normal way I would workout this question if it didn't mention pH change is:

mol H+ = (100)/(1000) *0.2 = 0.02

mol OH- = 50/1000 * 0.1= 0.005

Xs Mol H+ = 0.02- 0.005 = 0.015

Mol H+ = 0.015/ (150/1000) =0.1

pH= -log (0.1) = 1.

Not sure of what the change is though???
pH comes from concentration of H+ ions

Calculate the concentration initially ====> hence the pH

Calculate the concentration after some has been neutralised ====> hence the new pH

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