Answer: B. 1.5 × 10⁻¹⁸
Explanation:
Concept:
When multiplying exponents, add the exponents together.
When dividing exponents, subtract the exponents.
When converting scientific notation to an integer:
- If the exponent is negative, move the decimal to the left with the same amount of units as the exponents.
- For example: If converting 5 × 10⁻³, since the exponent is -3, we move the decimal to the left 3 units
- If the exponent is positive, move the decimal to the right with the same amount of units as the exponents
- For example: If converting 2 × 10⁴, since the exponent is 4, we move the decimal to the right 4 units
When converting an integer to scientific notation:
- If the number is ≥1, then count the moves of decimal point until the integer is 0<integer<10. The number of moves will be the exponent that is positive.
- For example: If converting 300, since there are two moves until it is left with 0<3<10. Thus, the scientific notation will be 3 × 10²
- If the number is <1, then count the moves of decimal point until the integer is 0<integer<10. The number of moves will be the exponent that is negative.
- For example: If converting 0.004, since there are three moves until it is left with 0<4<10. Thus, the scientific notation will be 4 × 10⁻³
Given:
Mass of one water molecule = 3.0 × 10⁻²³
Total number of molecules (required by the question) = 50,000
Solve:
Formula
Total mass = Mass of one water molecule × Total number of molecules
Substitute the values into the formula
Total mass = 3.0 × 10⁻²³ × 50,000
Convert 50,000 into scientific notation
Total mass = 3.0 × 10⁻²³ × 5 × 10⁴
Multiply numbers together/ Multiply exponents together
Total mass = 15 × 10⁻¹⁹ = 1.5 × 10⁻¹⁸
Hope this helps!! :)
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