Astudent measures the ph of a solution to be 6.8. which should the student add if she wants to decrease the ph of the solution? nacl h2o hf koh

The neutral pH is 7. Less than 7 indicates an acid and more than 7 indicates a base (up to 14).
NaCl - it's a salt (we can't measure the pH)
H2O - it can be an acid but also a base  (the pH it is almost neutral,meaning close to 7 )
HF - it is a strong acid
KOH  - it is a strong base (pH=14)

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He needs to use HF (Hydrogen fluoride) to decrease the pH.

HF is the answer because it is an acid so it decreases overall ph. Did you understand?

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