Can you always tell by looking at a substance if it is pure or not? ​

nope

Explanation:

bcoz every thing we look that isn't real. some substance are chemically changed and some are physically changed.if the physical change occurs then it is temporary change and if chemical change occurs it is permanent change.

Conclusion:I can think this much with my tiny mind.

THANK YOU

answer; i do believe the correct answer is (river); /// good luck

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.