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27.3 MB (1.5 MB compressed)
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30.0 x 22.9 cm ⏐ 11.8 x 9.0 in (300dpi)
ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Using a pH meter. Schoolgirl using a pH meter on a solution of dilute ethanoic acid (CH3.COOH). The display shows an acidic pH of 4.90. A pH reading measures the concentration of free hydrogen ions. A pH below 7 (acidic) is a higher concentration of hydrogen ions than found in water (pH 7, neutral). A pH above 7 (alkaline) is a lower concentration than found in water.
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