Why is a mole not a weight?
A dozen is 12. A mole is 6.02 x 10^23. Practice dividing particle counts by Avogadro's number, and learn why the mole is not a weight.
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2 lessons for “Avogadro's number and the mole”
36 g of water: 2 moles or half a mole?
36.0 g of water is 2.00 mol, and 2.00 mol of CO2 is 88.0 g. Practice reading the units to choose divide or multiply.
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0.50 mol in 2.0 L: 0.25 M or 4 M?
Half a mole of salt in two liters of solution. Is the answer 0.25 M or 4 M? The definition settles it.
Try this lessonIs water's molar mass 17 or 18 g/mol?
The subscript 2 in H2O is easy to miss in a molar mass. Count it once, and every conversion after stays right.
Try this lessonWhy can't I just add 7 and 5?
Maya added -7 and 5 and got 12. She counted the sizes of both numbers but forgot that they move in opposite directions.
Try this lessonWhat do two negatives in a row do?
Priya multiplied -3 by -4 and wrote -12. She remembered that negatives matter, but she got the rule backwards.
Try this lessonWhat does minus a negative really mean?
Diego saw 5 - (-3) and wrote 2, as if the problem were 5 - 3. But the two minus signs are doing different jobs.
Try this lessonWhat does percent of really mean?
Ivan found 15% of 80 by computing 1.5 * 80 and wrote 120. He moved the decimal the wrong way when converting 15%.
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